Neural processing, perception, and behavioral responses to natural chemical stimuli by fish and crustaceans

Structure, transduction pathway, behavior and toxicity of fish olfactory in aquatic environments

The olfactory system in teleost fish plays a vital role as chemosensory organ that directly interacts with the aquatic environment, exhibiting high sensitivity to chemical alteration in aquatic environments. However, despite its importance, there has been a lack of systematic reviews in the past decade on fish olfactory structure, transduction mechanisms, and the impact of environmental pollutants on olfactory toxicity. This study analyzed 272 relevant studies, focusing on the role of the olfactory system and the disruption of olfactory function by contaminants. Fish processes odors through olfactory receptor neurons, olfactory nerves, mitral/ruffed cells, glomeruli, and neurotransmitters, mediated by membrane potentials resulting from ion channels in the olfactory epithelium and olfactory bulb, which are then relayed to higher brain regions via the medial olfactory tracts and lateral olfactory tracts for further integration and modulation. This process minimizes the overlap between complex odor sets, ensuring distinct representation of each odor and eliciting appropriate olfactory-mediated behaviors, such as feeding, migration, alarm responses, and reproduction. Current research identifies four main types of contaminants affecting the fish olfactory system: heavy metals (51.60 %), organic contaminants (33.79 %), acidification (12.33 %), and salinity (5.94 %). The main mechanisms of impact are: morphological changes (21.19 %), alterations in olfactory receptors (29.24 %), damage to olfactory receptor neurons and neurotransmitters disruption (26.69 %), plasticity (2.97 %), and defense mechanisms (19.92 %). We also identify uncertainties and proposes future research directions on the effects of contaminants on fish olfactory. Overall, this review provides valuable insights into the toxicity of contaminants on fish olfactory.

Predator cues and environmental complexity shape the behaviour and life history of juvenile lobsters (Homarus gammarus)

Phenotypic plasticity is critical for animals to survive in our rapidly changing world, especially for species with low population densities. Standard hatchery procedures can assist some conservation programmes by producing large numbers of juveniles to be released into the wild. Yet we know surprisingly little about the impact that such standard, minimalistic hatchery settings have on the development of important behaviours and life-history traits of the animals. Here, we fill this gap by testing whether and how early-life exposure to different environmental conditions alters the development of ecologically relevant behaviours and life-history traits of the European lobster (Homarus gammarus)-one of the most harvested species in the Mediterranean. We used the progeny of wild-caught females and manipulated-in a full factorial design-the environmental complexity of the individual enclosures and the level of perceived predation risk. We repeatedly quantified key behaviours (activity, shelter use and aggressiveness) and life-history traits (carapace length and intermoult period) of individuals throughout their early development, capturing both mean and individual-level variation across treatments. Our results offer solid evidence that standard hatchery settings compromise the development of important behavioural and life-history traits of lobsters and even alter their behavioural plasticity-probably reducing the effectiveness of conservation programmes.

Genomic insights into ORs gene family of G protein-coupled receptors expansion driving omnivorous feeding in Spotted knifejaw (Oplegnathus punctatus)

The Spotted knifejaw was previously considered a predominantly carnivorous species, but emerging evidence suggests that it exhibits omnivorous characteristics. However, the mechanisms underpinning its dietary remain poorly understood; Behavioral experiments have demonstrated that the fish shows preferences for both carnivorous and herbivorous foods and olfactory dysfunction was found to significantly reduced the responsiveness to food stimuli. Anatomical and histological analyses revealed a well-developed olfactory system, with increases in the number of olfactory lamellae and epithelial cells at 50 and 120 dph, which were consistent with spatio-temporal gene expression patterns. Genomic analyses identified ORs within the GPCR family, including 164 MORs, 77 TAARs, 4 V1Rs, and 7 V2Rs. Notably, a significant expansion of the δ subtype of MORs was observed suggesting a role in omnivorous adaptation. Transcriptomic WGCNA revealed the pathways related to protein digestion and absorption, pancreatic secretion, olfactory transduction, and gastric acid secretion. It is hypothesized that the expansion of TAAR13c is related to the carnivorous nature of O. punctatus. In situ hybridization confirmed the expression of key ORs in olfactory epithelial cells, sensory neurons, and intestinal endocrine cells, and functional validation of ORs using the dual luciferase assay, providing new insights into the molecular mechanisms governing omnivory in the Spotted knifejaw.

Genome-Wide Identification and Evolutionary Analysis of Ionotropic Receptors Gene Family: Insights into Olfaction Ability Evolution and Antennal Expression Patterns in Oratosquilla oratoria

Olfaction plays a crucial role in crustaceans for essential activities such as foraging and predator evasion. Among the components involved in olfactory perception, Ionotropic Receptors (IRs) are particularly important. Oratosquilla oratoria, a perennial crustacean of substantial economic and ecological value, serves as an ideal model for studying olfactory mechanisms. Identifying the IR chemosensory genes in O. oratoria enhances our understanding of its olfactory recognition system. Based on the whole-genome data of O. oratoria, we identified and analyzed 50 members of the IR gene family (OratIRs) through bioinformatics approaches. These genes were classified into subfamilies of co-receptor IRs and tuning IRs. The physicochemical properties of the encoded proteins exhibit marked variability, indicating distinct roles. The motif types and conserved domains among these subfamilies display certain similarities, but their gene structures differ markedly. Furthermore, we found that OratIR25a, OratIR07629, and OratIR14286 are key nodes in protein-protein interaction networks, coordinating organisms' responses to signals like temperature and acids. We utilized fluorescence in situ hybridization (FISH) to find that OratIR75-1 and OratIR8a demonstrated robust expression signals in the antennae of the O. oratoria. These findings lay a foundation for further investigations and elucidate the functional roles of olfactory receptor genes in crustaceans.

Behavioural changes of native freshwater prawn in the presence of a predator fish

Predation pressure influences animal behaviour in relation to feeding, exposure to predators and habitat use. In the presence of a predator, prey usually decreases feeding and activity, avoiding predation-risk areas. This study evaluated the visual effects of a predator fish (red-bellied piranha Pygocentrus nattereri) on the behaviour and habitat use of Macrobrachium jelskii prawn. It was hypothesized that prawns would modify their behaviour in the presence of a predator, decreasing their general activity (foraging and locomotion) and seeking shelter more frequently. Twenty behavioural tests were carried out without and with the presence of a predator using five different M. jelskii individuals per trial. Behavioural data were collected using scan sampling with instantaneous recording of behaviours every 15 s during 5 min in each trial. The presence of the predator caused prawns to decrease their locomotion and feeding and increase environment exploration and predator inspection. Prawns used the shelter more frequently when the predator was present. Red-bellied piranha elicited anti-predator behaviour in M. jelskii. The patterns observed suggested that the most common anti-predatory behaviours exhibited by M. jelskii are beneficial as they reduce vigilance and active anti-predation strategies, such as escape.

Inclusion Effect of Various Levels of Jack Mackerel Meal in Olive Flounder (Paralichthys olivaceus) Diets Substituting 50% Fish Meal with Duck By-Product Meal on Growth and Feed Utilization

This experiment was performed to evaluate the inclusion impact of various levels of jack mackerel meal (JMM) in olive flounder (P. olivaceus) feeds substituting 50% FM by duck by-product meal (DBM) on growth, feed availability, and economic efficiency. Seven experimental diets were prepared. The control (Con) diet contained 60% FM. Fifty percent FM in the Con diet was substituted with DBM, and then the graded levels (0%, 10%, 20%, 30%, 40%, and 50%) of JMM were added instead of FM, named the DJ0, DJ10, DJ20, DJ30, DJ40, and DJ50 diets, respectively. All feeds were assigned to triplicate fish groups. At the end of 56 days' feeding, fish fed the DJ40 and DJ50 diets exhibited comparable weight gain and specific growth rate to fish fed the Con diet. Higher feed consumption was observed in fish fed the Con, DJ40, and DJ50 diets compared to fish fed the DJ0 and DJ10 diets. Lower feed conversion ratio was observed in fish fed the Con diet compared to fish fed the DJ0, DJ10, DJ20, and DJ30 diets. Furthermore, the DJ50 diet led to the highest economic profit index (EPI). In conclusion, inclusion of 50% JMM in the olive flounder diet replacing 50% FM with DBM seems to be the most recommendable dietary treatment based on growth and feed consumption of olive flounder and EPI.

Integration of transcriptome, gut microbiota, and physiology reveals toxic responses of the red claw crayfish (Cherax quadricarinatus) to imidacloprid

Imidacloprid enters the water environment through rainfall and causes harm to aquatic crustaceans. However, the potential chronic toxicity mechanism of imidacloprid in crayfish has not been comprehensively studied. In this study, red claw crayfish (Cherax quadricarinatus) were exposed to 11.76, 35.27, or 88.17 μg/L imidacloprid for 30 days, and changes in the physiology and biochemistry, gut microbiota, and transcriptome of C. quadricarinatus and the interaction between imidacloprid, gut microbiota, and genes were studied. Imidacloprid induced oxidative stress and decreased growth performance in crayfish. Imidacloprid exposure caused hepatopancreas damage and decreased serum immune enzyme activity. Hepatopancreatic and plasma acetylcholine decreased significantly in the 88.17 μg/L group. Imidacloprid reduced the diversity of the intestinal flora, increased the abundance of harmful flora, and disrupted the microbiota function. Transcriptomic analysis showed that the number of up-and-down-regulated differentially expressed genes (DEGs) increased significantly with increasing concentrations of imidacloprid. DEG enrichment analyses indicated that imidacloprid inhibits neurotransmitter transduction and immune responses and disrupts energy metabolic processes. Crayfish could alleviate imidacloprid stress by regulating antioxidant and detoxification-related genes. A high correlation was revealed between GST, HSPA1s, and HSP90 and the composition of gut microorganisms in crayfish under imidacloprid stress. This study highlights the negative effects and provides detailed sequencing data from transcriptome and gut microbiota to enhance our understanding of the molecular toxicity of imidacloprid in crustaceans.

Extreme olfactory sensitivity of silver and bighead carp to overlapping suites of 21-carbon steroids suggests that these species, and likely all other Cyprinoidei, employ them as pheromones

Although well established that several fishes including goldfish in the suborder Cypinoidei within the family Cypriniformes use the maturation-inducing steroid 17,20β-dihydroxy-pregn-4-ene-3-one (17,20βP) and its metabolites as a priming pheromone which they detect with sensitivity and specificity, it is unclear whether and how other Cypriniformes might have evolved to do so. This study examined this question in the family Xenocyprididae. Using electro-olfactogram recording we tested the olfactory sensitivity of silver (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) to a range of 213 steroids in 21 mixtures at 10-9M. While silver carp detected 6 of 21 mixtures, bighead carp detected 5 (p< 0.05). Silver carp were sensitive to 13 21-carbon steroids in these mixtures including 17,20βP while bighead carp detected 9, including 8 detected by silver carp. This assortment of steroids overlapped that detected by goldfish (family Cyprinidae) but no non-Cyprinoid, suggesting common evolutionary origin and function with differences characteristic of species-specificity.

Catfishes: A global review of the literature

This study aims to elucidate the evolution of catfish research publications over recent decades, identify emerging research clusters, examine keyword patterns, determine major contributors (including authors, organizations, and funding agencies), and analyze their collaborative networks and citation bursts on a global scale. The USA, Brazil, China, and India collectively contribute approximately 67% of the total catfish research publications, with a marked increase in prevalence since 2016. The most frequently occurring and dominant keywords are "channel catfish" and "responses," respectively. Intriguingly, our findings reveal 28 distinct article clusters, with prominent clusters including "yellow catfish," "channel catfish", "pectoral girdle," "African catfish", "Rio Sao Francisco basin," "Edwardsiella ictaluri," and "temperature mediated". Concurrently, keyword clustering generates seven main clusters: "new species", "growth performance", "heavy metal", "gonadotropin-releasing", "essential oil", and "olfactory receptor". This study further anticipates future research directions, offering fresh perspectives on the catfish literature landscape. To the best of our knowledge, this is the first article to conduct a comprehensive mapping review of catfish research publications worldwide.

Species-specific metabolites mediate host selection and larval recruitment of the symbiotic seastar shrimp

In marine environments, host selection, defining how symbiotic organisms recognize and interact with their hosts, is often mediated by olfactory communication. Although adult symbionts may select their hosts detecting chemosensory cues, no information is available concerning the recruitment of symbiotic larvae which is a crucial step to sustain symbioses over generations. This study investigates the olfactory recognition of seastar hosts by adult Zenopontonia soror shrimps and the recruitment of their larvae. We examine the semiochemicals that influence host selection using chemical extractions, behavioural experiments in olfactometers, and mass spectrometry analyses. After describing the symbiotic population and the embryonic development of shrimps, our results demonstrate that asterosaponins, which are traditionally considered as chemical defences in seastars, are species-specific and play a role in attracting the symbiotic shrimps. Adult shrimps were found to be attracted only by their original host species Culcita novaeguineae, while larvae were attracted by different species of seastars. This study provides the first chemical identification of an olfactory cue used by larvae of symbiotic organisms to locate their host for recruitment. These findings highlight the importance of chemical communication in the mediation of symbiotic associations, which has broader significant implications for understanding the ecological dynamics of marine ecosystems.

Aerosol Alteration of Behavioral Response to Pheromone in Bombyx mori

Because of the complexity to study them, aerosols have been neglected in nearly all studies on olfaction, especially studies dealing with odor capture. However, aerosols are present in large quantities in the atmosphere and have the physico-chemical ability to interact with odor molecules, in particular the many pheromones with low volatility. We submitted male moths of Bombyx mori to bombykol puffs, the main fatty alcohol component of its sex pheromone, depending on whether the air is free of aerosols, charged with ambient concentration aerosols or supplemented with aqueous aerosols and recorded their arousal behavior. Aerosols and pheromone do interact consistently over all experiments and moths react better in low aerosol-concentration conditions. We propose four hypotheses for explaining this impediment, the two most likely resorting to competition between odor molecules and aerosols for the olfactory pores and postulate a reversal to a positive impact of aerosols on communication, depending on the particular physico-chemical properties of the multiphasic interaction. Studying the partitioning between gas and particulate phases in the transport and reception of odors is key for advancing the chemico-physical understanding of olfaction.

Host habitat shapes the core gut bacteria of decapod crustaceans: A meta-analysis

Gut microbiota is an essential determinant factor that drives the physiological, immunological, and metabolic functions of animals. A few meta-analysis studies identified crucial information about the gut microbiota of vertebrate animals in different habitats including fish while no report is yet available for the commercially cultured decapod crustaceans (DC). This meta-analysis investigated the gut microbiota of 11 commercially cultured DC species from five different groups-crab, crayfish, lobster, prawn, and shrimp to gain an overview of microbial diversity and composition and to find out core genera under two different host habitats: freshwater and saltwater. The analysis of 627 Illumina datasets from 25 published studies revealed selective patterns of diversity and compositional differences among groups and between freshwater and saltwater culture systems. The study found a salinity-dependent heterogeneous response of gut microbiota, specifically Vibrio in saltwater for white shrimp, a species that can be cultured with and without salt. Overall, the genera reared in freshwater showed higher diversity in the gut microbial communities than those reared in saltwater. An overwhelming abundance of Candidatus Bacilloplasma and Vibrio were identified for species cultured in freshwater and saltwater system, respectively and these two species were identified as the main core genera for nine out of 11 DC species, except freshwater prawn and river prawn. Together, these results demonstrate the effectiveness of the meta-analysis in identifying the robust and reproducible features of DC gut microbiota for different groups and host habitats. The diversity information curated here could be used as a reference for future studies to differentiate various DC species under two different rearing environments.

HPLC-MS-based untargeted metabolomic analysis of differential plasma metabolites and their associated metabolic pathways in reproductively anosmic black porgy, Acanthopagrus schlegelii

Olfaction, a universal form of chemical communication, is a powerful channel for animals to obtain social and environmental cues. The mechanisms by which fish olfaction affects reproduction, breeding and disease control are not yet clear. To evaluate metabolites profiles, plasma from anosmic and control black porgy during reproduction was analyzed by non-targeted metabolomics using ultra high-performance liquid chromatography-mass spectrometry and multivariate statistical analysis techniques, including principal component analysis and orthogonal partial least squares discriminant analysis. The metabolite profiles of anosmia and control groups were found to be significantly separated. Ten different differential metabolites, mainly including amino acids, such as isoleucine and methionine, and lipids, such as phosphatidylserine, were screened based on the combined analysis of variable importance in the projection and p values. In addition, six key differential metabolic pathways were analyzed using the Kyoto Encyclopedia of Genes and Genomes and enriched for four metabolic pathways including the citrate acid (TCA) cycle, tyrosine metabolism, arginine and proline metabolism, and arginine synthesis. The TCA cycle enhances fertility through the reduction of pyruvate kinase, and intermediate derivatives (acetyl CoA, malonyl CoA) act as signaling factors that regulate immune cell function. The tyrosine cycle can indirectly participate and promote reproduction in black porgy through melanin-concentrating hormone. Arginine and proline metabolism can promote reproduction by promoting growth hormone and enhance immunity in anosmic black porgy by stimulating T lymphocytes. Our metabolomic study revealed that anosmia in black porgy played an active role in immunity and reproduction and provided theoretical support for breeding and disease control.

High temperatures enhance the strength of multiple predator effects in a typical crab-clam system

Although marine heatwaves pose urgent threats to marine life, our understanding of how these events influence interactions between key species in marine ecosystems is still inadequate. Herein, we examined the behavioral mechanisms by which heat regulates multiple predator effects in different foraging systems that include Asian paddle crabs (Charybdis japonica) and swimming crabs (Portunus trituberculatus) by quantifying their predation and competition at two temperatures. Our results show that non-independent multiple predator effects occurred in the conspecific treatment of Asian paddle crabs and in the interspecific treatment, whereas independent multiple predator effects occurred in the conspecific treatment of swimming crabs. Asymmetrical behavior responses of these crabs to competition and heat triggered divergences in multiple predator effects. High temperatures increased the strength of multiple predator effects but did not alter their types. The reason is that heat negatively impacts predation by enhancing aggressive interactions, outweighing its direct positive effects on predation.

What do oysters smell? Electrophysiological evidence that the bivalve osphradium is a chemosensory organ in the oyster, Magallana gigas

The sensing of chemical cues is essential for several aspects of bivalve biology, such as the detection of food and pheromones. However, little is known about chemical communication systems in bivalves or the possible role of the osphradium as a chemosensory organ. To address this, we adapted an electrophysiological technique extensively used in vertebrates-the electro-olfactogram-to record from the osphradium in the Pacific oyster, Magallana gigas. This technique was validated using amino acids as stimulants. The osphradium proved to be sensitive to most proteinogenic L-amino acids tested, evoking tonic, negative, concentration-dependent 'electro-osphradiogram' (EOsG) voltage responses, with thresholds of detection in the range of 10^- 6 to 10^- 5 M. Conversely, it was insensitive to L-arginine and L-glutamic acid. The current study supports the hypothesis that the osphradium is, indeed, a chemosensory organ. The 'electro-osphradiogram' may prove to be a powerful tool in the isolation and characterization of pheromones and other important chemical cues in bivalve biology.

Development of a two-current choice flume behavioural bioassay for juvenile Panulirus ornatus response to moulting cues

Characterising crustacean behaviour in response to conspecific chemical cues contributes to our evolving knowledge of the drivers of their social behaviour. There is particular interest in understanding the chemical and behavioural mechanisms contributing to cannibalism at ecdysis, as this behaviour substantially limits culture productivity of several commercially important crustaceans. Before investigating the role of chemoreception in cannibalism of moulting crustaceans, we must investigate its role in detecting moulting conspecifics. Here we use a two-current choice flume to observe juvenile tropical rock lobster (Panulirus ornatus) behavioural response to conspecific moulting cues and identifying attracted and avoidant behaviours correlating to moult stage and social relationship. Observed cue preferences show inter-moult juveniles are attracted to the moulting cues of lobsters to which they are socially naïve. In contrast, post-moult and inter-moult juveniles avoid the moulting cues of individuals whom they are socially familiar with. Average speed and total distance travelled by lobsters increases in response to conspecific moulting cues. This study demonstrates the suitability of a two-current choice flume for behavioural assays in P. ornatus and characterises clear behavioural patterns in juveniles exposed to conspecific moulting cues. This provides important framework for understanding the role of chemical communication in eliciting cannibalism.

Aquatic insects differentially affect lake sturgeon larval phenotypes and egg surface microbial communities

Documentation of how interactions among members of different stream communities [e.g., microbial communities and aquatic insect taxa exhibiting different feeding strategies (FS)] collectively influence the growth, survival, and recruitment of stream fishes is limited. Considerable spatial overlap exists between early life stages of stream fishes, including species of conservation concern like lake sturgeon (Acipenser fulvescens), and aquatic insects and microbial taxa that abundantly occupy substrates on which spawning occurs. Habitat overlap suggests that species interactions across trophic levels may be common, but outcomes of these interactions are poorly understood. We conducted an experiment where lake sturgeon eggs were fertilized and incubated in the presence of individuals from one of four aquatic insect FS taxa including predators, facultative and obligate-scrapers, collector-filterers/facultative predators, and a control (no insects). We quantified and compared the effects of different insect taxa on the taxonomic composition and relative abundance of egg surface bacterial and lower eukaryotic communities, egg size, incubation time to hatch, free embryo body size (total length) at hatch, yolk-sac area, (a measure of resource utilization), and percent survival to hatch. Mean egg size varied significantly among insect treatments. Eggs exposed to predators had a lower mean percent survival to hatch. Eggs exposed to predators had significantly shorter incubation periods. At hatch, free embryos exposed to predators had significantly smaller yolk sacs and total length. Multivariate analyses revealed that egg bacterial and lower eukaryotic surface community composition varied significantly among insect treatments and between time periods (1 vs 4 days post-fertilization). Quantitative PCR documented significant differences in bacterial 16S copy number, and thus abundance on egg surfaces varied across insect treatments. Results indicate that lethal and non-lethal effects associated with interactions between lake sturgeon eggs and free embryos and aquatic insects, particularly predators, contributed to lake sturgeon trait variability that may affect population levels of recruitment.

Microplastics in the tissues of commercial semi-intensive shrimp pond-farmed Litopenaeus vannamei from the Gulf of California ecoregion

The omnipresence of microplastics (MPs) in marine and coastal environments has attracted attention owing to their effects on various organisms, including humans. We present the first study of MPs in the gastrointestinal tract (GT), gills (GI), and exoskeleton (EX) of the farmed whiteleg shrimp Litopenaeus vannamei from commercial aquaculture facilities in northwestern Mexico that have operated semi-intensively for the last two decades. We found that the number of MP items per tissue was 7.6 ± 0.6 in the GT, 6.3 ± 0.9 in the GI, and 4.3 ± 0.9 in the EX, with an average of 18.5 ± 1.2 MP items per shrimp (1.06 items/g, wet weight [ww]). MP concentrations were 261.7 ± 84.5, 13.1 ± 1.8, and 2.6 ± 0.6 items/g (ww) in the GT, GI, and EX, respectively. Microplastics ranged from 30 to 2800 μm in size (360 ± 39 μm) with fibers (∼90.8%), filament-shape (∼93.4%), and transparent (∼47.7%) being the most common ones. Polyethylene (∼54.5%) and polyamide (∼24.2%) were the most commonly identified polymers, although polyesters (∼12.1%), polystyrene (∼6.1%), and nylon (∼3.0%) were also found. The abundance of MPs in farmed L. vannamei may be related to their feeding habits and the availability of MP sources in aquaculture facilities.

Unveiling social distancing mechanisms via a fish-robot hybrid interaction

Pathogen transmission is a major limit of social species. Social distancing, a behavioural-based response to diseases, has been regularly reported in nature. However, the identification of distinctive stimuli associated with an infectious disease represents a challenging task for host species, whose cognitive mechanisms are still poorly understood. Herein, the social fish Paracheirodon innesi, was selected as model organism to investigate animal abilities in exploiting visual information to identify and promote social distancing towards potentially infected conspecifics. To address this, a robotic fish replica mimicking a healthy P. innesi subject, and another mimicking P. innesi with morphological and/or locomotion anomalies were developed. P. innesi individuals were attracted by the healthy fish replica, while they avoided the fish replica with morphological abnormalities, as well as the fish replica with an intact appearance, but performing locomotion anomalies (both symptoms associated with a microsporidian parasite infesting P. innesi and other fish). Furthermore, the fish replica presenting both morphology and locomotion anomalies in conjunction, triggered a significantly stronger social distancing response. This confirms the hypothesis that group living animals overgeneralize cues that can be related with a disease to minimize transmission, and highlights the important role of visual cues in infection risk contexts. This study prompts more attention on the role of behavioural-based strategies to avoid pathogen/parasite diffusion, and can be used to optimize computational approaches to model disease dynamics.

The effects of vesicle toxin from the sea anemone Bunodosoma cangicum on the behavior of a freshwater shrimp, Palaemon argentinus, and shore crab, Neohelice granulata

Sea anemones of the genus Bunodosoma possess along their body column, longitudinally arranged brown-colored vesicles. We have shown that in B. cangicum, these warty structures contain a mixture of potent toxins. This work highlights the neuro-inhibitory effects exhibited by two decapod crustacean species exposed to the extracts from these vesicles. For this, we use the unrefined toxin in doses, exposure times, and different exposure pathways. The findings show that at least one neuro-inhibitory compound is present and remains active regardless of the exposure method or dose tested. This toxin affects neuro-motor pathways but not neuro-sensory pathways. Shrimp exposed to toxin could continue to perceive and track food pellets but could not secure and consume their ration. Of six anatomical reflexes tested under the toxin's influence, voluntary movements of the mouthparts were impacted most commonly. Interestingly, all subject animals recovered from the toxin exposure within 2 h. Finally, we propose Reflexive Action Analysis (RAMP) as a tool to evaluate the potency of other neurotoxic or neuro-inhibitory compounds in crustacea. This work is the first to show the neuro-inhibitory activity of extracts from these sea anemone columnar vesicle structures and the first to evaluate these effects using RAMP reflex analysis.

Nutrition and Functions of Amino Acids in Fish

Aquaculture is increasingly important for providing humans with high-quality animal protein to improve growth, development and health. Farm-raised fish and shellfish now exceed captured fisheries for foods. More than 70% of the production cost is dependent on the supply of compound feeds. A public debate or concern over aquaculture is its environmental sustainability as many fish species have high requirements for dietary protein and fishmeal. Protein or amino acids (AAs), which are the major component of tissue growth, are generally the most expensive nutrients in animal production and, therefore, are crucial for aquatic feed development. There is compelling evidence that an adequate supply of both traditionally classified nutritionally essential amino acids (EAAs) and non-essential amino acids (NEAAs) in diets improve the growth, development and production performance of aquatic animals (e.g., larval metamorphosis). The processes for the utilization of dietary AAs or protein utilization by animals include digestion, absorption and metabolism. The digestibility and bioavailability of AAs should be carefully evaluated because feed production processes and AA degradation in the gut affect the amounts of dietary AAs that enter the blood circulation. Absorbed AAs are utilized for the syntheses of protein, peptides, AAs, and other metabolites (including nucleotides); biological oxidation and ATP production; gluconeogenesis and lipogenesis; and the regulation of acid-base balance, anti-oxidative reactions, and immune responses. Fish producers usually focus on the content or digestibility of dietary crude protein without considering the supply of AAs in the diet. In experiments involving dietary supplementation with AAs, inappropriate AAs (e.g., glycine and glutamate) are often used as the isonitrogenous control. At present, limited knowledge is available about either the cell- and tissue-specific metabolism of AAs or the effects of feed processing methods on the digestion and utilization of AAs in different fish species. These issues should be addressed to develop environment-friendly aquafeeds and reduce feed costs to sustain the global aquaculture.

Feed Intake as an Estimation of Attractability in Pacific White Shrimp Litopenaeus vannamei

A simple bioassay that quantifies feed intake as an estimation of relative attractability of feeds containing different ingredients in the Pacific white shrimp Litopenaeus vannamei is described. Fish meal (FM), fish protein hydrolysate (FPH), squid meal (SqM) and casein (CN) were assessed at the same dietary level for their relative influence on feed intake rates of Litopenaeus vannamei. A bland diet containing 92% whole wheat grain meal, 6% diatomaceous earth and 2% alginate with a known low attractability was used as the standard control or base diet. Ingredients were added to the bland base control diet at a level of 3% as fed. Shrimp were stocked into 80 L glass tanks (n= 20 per tank) in a recirculating aquaculture system. Tanks were randomly assigned to one of five diet treatments (3tanks/treatment). Experiments measuring the attractability of each feed were conducted twice daily at 0900 hours and 1330 hours over a five day period. For each experiment, 40 feed pellets (ca. 1 g) corresponding to the assigned treatment were provided to each tank. To calculate the rate of feed intake, pellets remaining in each tank were counted at six minute intervals for a seventy-two minute period. Differences in rate of feed intake among diets were evaluated using Cox Regression Analysis. This attractability assay required only small amounts of ingredients and incorporated ingredients into a bland feed, which significantly reduces the influence from other ingredients or compound in the pellets. All of the test protein ingredients, especially SqM, in the feeds significantly increased the feed consumption rate. The diet containing SqM was consumed at a significantly higher rate than those containing casein and FM but not FPH. FPH and CN containing diets were not significantly different but consumed at a higher rate than the diet containing FM. Results of these trials indicate that the presence of certain ingredients can increase feed intake, thereby increasing nutrient availability of the diets. This reported method to determine consumption of diets containing certain ingredients can be considered as a valid method to estimate attractability.

Why Protect Decapod Crustaceans Used as Models in Biomedical Research and in Ecotoxicology? Ethical and Legislative Considerations

Simple Summary

Current European legislation that protects animals used for scientific purposes excludes decapod crustaceans (for example, lobster, crab and crayfish) on the grounds that they are non-sentient and, therefore, incapable of suffering. However, recent work suggests that this view requires substantial revision. Our current understanding of the nervous systems and behavior of decapods suggests an urgent need to amend and update all relevant legislation. This paper examines recent experiments that suggest sentience and how that work has changed current opinion. It reflects on the use of decapods as models in biomedical research and in ecotoxicology, and it recommends that these animals should be included in the European protection legislation.

Abstract

Decapod crustaceans are widely used as experimental models, due to their biology, their sensitivity to pollutants and/or their convenience of collection and use. Decapods have been viewed as being non-sentient, and are not covered by current legislation from the European Parliament. However, recent studies suggest it is likely that they experience pain and may have the capacity to suffer. Accordingly, there is ethical concern regarding their continued use in research in the absence of protective measures. We argue that their welfare should be taken into account and included in ethical review processes that include the assessment of welfare and the minimization or alleviation of potential pain. We review the current use of these animals in research and the recent experiments that suggest sentience in this group. We also review recent changes in the views of scientists, veterinary scientists and animal charity groups, and their conclusion that these animals are likely to be sentient, and that changes in legislation are needed to protect them. A precautionary approach should be adopted to safeguard these animals from possible pain and suffering. Finally, we recommend that decapods be included in the European legislation concerning the welfare of animals used in experimentation.

Amino acid compounds released by the giant freshwater prawn Macrobrachium rosenbergii during ecdysis: a factor attracting cannibalistic behaviour?

Ecdysis is a common phenomenon that happens throughout the life phase of the giant freshwater prawn Macrobrachium rosenbergii. It is vital to better understand the correlation between cannibalism and biochemical compound that exists during the moulting process. The objective of the present study was to determine the amino acid profile released by M. rosenbergii during the ecdysis process that promotes cannibalism. To accomplish this, changes in amino acid levels (total amino acid (TAA) and free amino acid (FAA)) of tissue muscle, exoskeleton, and sample water of culture medium from the moulting (E-stage) and non-moulting (C-stage) prawns were analysed using high-performance liquid chromatography (HPLC). Comparison study revealed that among the TAA compounds, proline and sarcosine of tissues from moulting prawn were found at the highest levels. The level of FAA from water that contains moulting prawns (E-stage) was dominated by tryptophan and proline. Significant values obtained in the present study suggested that these amino acid compounds act as a chemical cue to promote cannibalism in M. rosenbergii during ecdysis. The knowledge of compositions and compounds that were released during the moulting process should be helpful for better understanding of the mechanism and chemical cues that play roles on triggering cannibalism, and also for future dietary manipulation to improve feeding efficiencies and feeding management, which indirectly impacts productivity and profitability.

Volatile fatty acid and aldehyde abundances evolve with behavior and habitat temperature in Sceloporus lizards

Animal signals evolve by striking a balance between the need to convey information through particular habitats and the limitations of what types of signals can most easily be produced and perceived. Here, we present new results from field measures of undisturbed behavior and biochemical analyses of scent marks from 12 species of Sceloporus lizards to explore whether evolutionary changes in chemical composition are better predicted by measures of species behavior, particularly those associated with visual displays, chemoreception, and locomotion, or by measures of habitat climate (precipitation and temperature). We found that more active lizard species used fewer compounds in their volatile scent marks, perhaps conveying less specific information about individual and species identity. Scent marks from more active lizard species also had higher proportions of saturated fatty acids, and the evolution of these compounds has been tracking the phylogeny closely as we would expect for a metabolic byproduct. In contrast, the proportions of unsaturated fatty acids were better explained by evolutionary shifts in habitat temperature (and not precipitation), with species in warmer climates using almost no volatile unsaturated fatty acids. The proportion of aldehydes was explained by both behavior and environment, decreasing with behavioral activity and increasing with habitat temperature. Our results highlight the evolutionary flexibility of complex chemical signals, with different chemical compounds responding to different elements of the selective landscape over evolutionary time.

Risk of triclosan based on avoidance by the shrimp Palaemon varians in a heterogeneous contamination scenario: How sensitive is this approach?

As the exposure of organisms to contaminants can provoke harmful effects, some organisms try to avoid a continuous exposure by using different strategies. The aim of the current study was to assess the ability of the shrimp Palaemon varians to detect a triclosan gradient and escape to less contaminated areas. Two multi-compartmented exposure systems (the linear system and the HeMHAS-Heterogeneous Multi-Habitat Assay System) were used and then results were compared. Finally, it was aimed how sensitive the avoidance response is by comparing it with other endpoints through a sensitivity profile by biological groups and the species sensitive distribution. The distribution of the shrimps along the triclosan gradient was dependent on the concentrations, not exceeding 3% for 54 μg/L in the linear system and 7% for 81 μg/L in the HeMHAS; 25% of organisms preferred the compartment with the lowest concentrations in both systems. Half of the population seems to avoid concentrations around 40-50 μg/L. The triclosan concentration that might start (threshold) to trigger an important avoidance (around 20%) was estimated to be of 18 μg/L. The profile of sensitivity to triclosan showed that avoidance by shrimps was less sensitive than microalgae growth and avoidance by guppy; however, it might occur even at concentrations considered safe for more than 95% of the species. In summary, (i) the HeMHAS proved to be a suitable system to simulate heterogeneous contamination scenarios, (ii) triclosan triggered the avoidance response in P. varians, and (iii) the avoidance was very sensitive compared to other ecotoxicological responses.

Effects of Dietary Inclusion of Shrimp Paste on Growth Performance, Digestive Enzymes Activities, Antioxidant and Immunological Status and Intestinal Morphology of Hybrid Snakehead (Channa maculata ♀ × Channa argus ♂)

A nutritional feeding experiment was conducted to evaluate the effects of shrimp paste on feeding attractiveness, growth performance, digestive enzyme activities, immune-related genes and intestinal morphology in hybrid snakehead (Channa maculata ♀ × Channa argus ♂). Two diets were formulated with or without shrimp paste supplementation (D1:0% and D2: 3%) to feed fish for 8 weeks. Results showed that growth performance (FBW, WG and SGR) and feed intake (FI) significantly increased with shrimp paste supplemented (P < 0.05), while FCR and SR of hybrid snakehead fed diets supplemented with shrimp paste or not showed no significant difference (P > 0.05). Gut lipase and amylase activities were significantly higher in diet supplemented with shrimp paste than that in control one (P < 0.05). Hepatic antioxidant statuses of hybrid snakehead fed dietary shrimp paste or not showed no significant differences in total antioxidant capacity, malondialdehyde and superoxide dismutase of fish (P > 0.05). Results showed that fish fed diet with shrimp paste supplemented did not show significant difference in expression of GR, IκB, P65 and IL8 than that in control group (P > 0.05). There are significantly more goblet cells in shrimp paste supplemented diet than that in control diet (P < 0.05). However, villi length and muscle thickness showed no significant difference compared to control diet (P > 0.05). The results indicated that dietary 3% shrimp paste supplementation improved the growth performance of hybrid snakehead by enhancing feed intake (FI) while made no difference to antioxidant capacity and immunity.

The Suitability of Fishes as Models for Studying Appetitive Behavior in Vertebrates

Fish have proven to be valuable models in the study of the endocrine control of appetite in response to peripheral signals of energetic and nutritional status. In parallel, a growing body of literature points to the importance of sensory experiences as factors affecting food choice in fish, with a special focus on visual and chemical signals allowing discrimination of potential foods within a 3D environment. Accordingly, waterborne compounds, such as monosaccharides or amino acids, are regarded as the main "olfactory" cues driving fish alimentary behavior. However, we recently suggested that hydrophobic molecules also allow food identification in aquatic environments and that fish actually explore a larger variety of chemosensory cues, including the olfactory/volatile compounds, when determining food palatability. In this study, we show that both homeostatic and chemosensory mechanisms involved in food intake are highly conserved in vertebrates and that the chemosensory world of fish is less different from that of terrestrial mammals than commonly thought. As a result, we support a more integrated and synthetic view of the mechanisms of chemical communication in both terrestrial and aquatic systems, which could help to ensure greater translatability of the fish models, such as the zebrafish (Danio rerio), the turquoise killifish (Nothobranchius furzeri), the goldfish (Carassius auratus), or the Japanese medaka fish (Oryzias latipes) to terrestrial vertebrates when approaching complex dynamic patterns in alimentary behavior.

Parasite avoidance behaviours in aquatic environments

Parasites, including macroparasites, protists, fungi, bacteria and viruses, can impose a heavy burden upon host animals. However, hosts are not without defences. One aspect of host defence, behavioural avoidance, has been studied in the terrestrial realm for over 50 years, but was first reported from the aquatic environment approximately 20 years ago. Evidence has mounted on the importance of parasite avoidance behaviours and it is increasingly apparent that there are core similarities in the function and benefit of this defence mechanism between terrestrial and aquatic systems. However, there are also stark differences driven by the unique biotic and abiotic characteristics of terrestrial and aquatic (marine and freshwater) environments. Here, we review avoidance behaviours in a comparative framework and highlight the characteristics of each environment that drive differences in the suite of mechanisms and cues that animals use to avoid parasites. We then explore trade-offs, potential negative effects of avoidance behaviour and the influence of human activities on avoidance behaviours. We conclude that avoidance behaviours are understudied in aquatic environments but can have significant implications for disease ecology and epidemiology, especially considering the accelerating emergence and re-emergence of parasites.This article is part of the Theo Murphy meeting issue 'Evolution of pathogen and parasite avoidance behaviours'.

Discovery and characterization of natural products that act as pheromones in fish

Covering: up to 2018 Fish use a diverse collection of molecules to communicate with conspecifics. Since Karlson and Lüscher termed these molecules 'pheromones', chemists and biologists have joined efforts to characterize their structures and functions. In particular, the understanding of insect pheromones developed at a rapid pace, set, in part, by the use of bioassay-guided fractionation and natural product chemistry. Research on vertebrate pheromones, however, has progressed more slowly. Initially, biologists characterized fish pheromones by screening commercially available compounds suspected to act as pheromones based upon their physiological function. Such biology-driven screening has proven a productive approach to studying pheromones in fish. However, the many functions of fish pheromones and diverse metabolites that fish release make predicting pheromone identity difficult and necessitate approaches led by chemistry. Indeed, the few cases in which pheromone identification was led by natural product chemistry indicated novel or otherwise unpredicted compounds act as pheromones. Here, we provide a brief review of the approaches to identifying pheromones, placing particular emphasis on the promise of using natural product chemistry together with assays of biological activity. Several case studies illustrate bioassay-guided fractionation as an approach to pheromone identification in fish and the unexpected diversity of pheromone structures discovered by natural product chemistry. With recent advances in natural product chemistry, bioassay-guided fractionation is likely to unveil an even broader collection of pheromone structures and enable research that spans across disciplines.

Male dominance status regulates odor-evoked processing in the forebrain of a cichlid fish

The ability to identify odors in the environment is crucial for survival and reproduction. However, whether olfactory processing in higher-order brain centers is influenced by an animal's physiological condition is unknown. We used in vivo neuron and local field potential (LFP) recordings from the ventral telencephalon of dominant and subordinate male cichlids to test the hypothesis that response properties of olfactory neurons differ with social status. Dominant males had a high percentage of neurons that responded to several odor types, suggesting broad tuning or differential sensitivity when males are reproductively active and defending a territory. A greater percentage of neurons in dominant males also responded to sex- and food-related odors, while a greater percentage of neurons in subordinate males responded to complex odors collected from behaving dominant males, possibly as a mechanism to mediate social suppression and allow subordinates to identify opportunities to rise in rank. Odor-evoked LFP spectral densities, indicative of synaptic inputs, were also 2-3-fold greater in dominant males, demonstrating status-dependent differences in processing possibly linking olfactory and other neural inputs to goal-directed behaviors. For the first time we reveal social and reproductive-state plasticity in olfactory processing neurons in the vertebrate forebrain that are associated with status-specific lifestyles.

Behavioural responses of humpback whales to food-related chemical stimuli

Baleen whales face the challenge of finding patchily distributed food in the open ocean. Their relatively well-developed olfactory structures suggest that they could identify the specific odours given off by planktonic prey such as krill aggregations. Like other marine predators, they may also detect dimethyl sulfide (DMS), a chemical released in areas of high marine productivity. However, dedicated behavioural studies still have to be conducted in baleen whales in order to confirm the involvement of chemoreception in their feeding ecology. We implemented 56 behavioural response experiments in humpback whales using two food-related chemical stimuli, krill extract and DMS, as well as their respective controls (orange clay and vegetable oil) in their breeding (Madagascar) and feeding grounds (Iceland and Antarctic Peninsula). The whales approached the stimulus area and stayed longer in the trial zone during krill extract trials compared to control trials, suggesting that they were attracted to the chemical source and spent time exploring its surroundings, probably in search of prey. This response was observed in Iceland, and to a lesser extend in Madagascar, but not in Antarctica. Surface behaviours indicative of sensory exploration, such as diving under the stimulus area and stopping navigation, were also observed more often during krill extract trials than during control trials. Exposure to DMS did not elicit such exploration behaviours in any of the study areas. However, acoustic analyses suggest that DMS and krill extract both modified the whales' acoustic activity in Madagascar. Altogether, these results provide the first behavioural evidence that baleen whales actually perceive prey-derived chemical cues over distances of several hundred metres. Chemoreception, especially olfaction, could thus be used for locating prey aggregations and for navigation at sea, as it has been shown in other marine predators including seabirds.

Sexually-Relevant Visual and Chemosensory Signals Induce Distinct Behaviors and Neural Activation Patterns in the Social African Cichlid, Astatotilapia burtoni

Across vertebrates, the use of multimodal (multiple sensory modalities) signals has evolved to convey important information to receivers. Information content of multimodal signals can be the same as or different from information in each unimodal signal, and are classified as redundant or non-redundant, respectively, based on receivers' behavioral responses. Despite the prevalence and importance of multimodal signaling across taxa, relatively little is known about how and where these signals are processed in the brains of receivers. We used the social African cichlid fish, Astatotilapia burtoni, to investigate how sexually-relevant visual and chemosensory uni- and multimodal signals from gravid (full of eggs) females influence behavior, brain activation patterns, and physiology in dominant males. We presented both visual and chemosensory signals either alone or together and found that males need sexually-relevant visual signals to engage in stereotypical courtship behaviors such as body quivers, waggles, and leads into spawning territories. However, the number of courtship behaviors was greater when males were exposed to multimodal visual-chemosensory signals, compared to either unimodal signal alone. When a female visual signal was absent, males increased swimming and overall activity in response to female-conditioned water compared to control water, suggesting that female-released chemosensory signals may stimulate male searching behavior and motivation. Importantly, we also tested anosmic (olfactory ablated) males to demonstrate that this behavior is primarily mediated by the olfactory system rather than gustation. Using the immediate early gene cfos as a proxy for neural activation, we also demonstrate differential activation in social and olfactory-relevant brain regions of dominant males exposed to unimodal and multimodal visual-chemosensory signals. We found at least one region that is preferentially activated by reception of signals from each sense, as well as regions that exhibit an additive effect on activation with multimodal visual-chemosensory stimulation. These data provide insight on how multimodal signals are processed in the brain and integrated with internal physiology of receivers to produce social behaviors, and lay the groundwork for future studies on the evolution of sensory perception.

The genome of the water strider Gerris buenoi reveals expansions of gene repertoires associated with adaptations to life on the water

BACKGROUND

Having conquered water surfaces worldwide, the semi-aquatic bugs occupy ponds, streams, lakes, mangroves, and even open oceans. The diversity of this group has inspired a range of scientific studies from ecology and evolution to developmental genetics and hydrodynamics of fluid locomotion. However, the lack of a representative water strider genome hinders our ability to more thoroughly investigate the molecular mechanisms underlying the processes of adaptation and diversification within this group.

RESULTS

Here we report the sequencing and manual annotation of the Gerris buenoi (G. buenoi) genome; the first water strider genome to be sequenced thus far. The size of the G. buenoi genome is approximately 1,000 Mb, and this sequencing effort has recovered 20,949 predicted protein-coding genes. Manual annotation uncovered a number of local (tandem and proximal) gene duplications and expansions of gene families known for their importance in a variety of processes associated with morphological and physiological adaptations to a water surface lifestyle. These expansions may affect key processes associated with growth, vision, desiccation resistance, detoxification, olfaction and epigenetic regulation. Strikingly, the G. buenoi genome contains three insulin receptors, suggesting key changes in the rewiring and function of the insulin pathway. Other genomic changes affecting with opsin genes may be associated with wavelength sensitivity shifts in opsins, which is likely to be key in facilitating specific adaptations in vision for diverse water habitats.

CONCLUSIONS

Our findings suggest that local gene duplications might have played an important role during the evolution of water striders. Along with these findings, the sequencing of the G. buenoi genome now provides us the opportunity to pursue exciting research opportunities to further understand the genomic underpinnings of traits associated with the extreme body plan and life history of water striders.

Whole-head recording of chemosensory activity in the marine annelid Platynereis dumerilii

Chemical detection is key to various behaviours in both marine and terrestrial animals. Marine species, though highly diverse, have been underrepresented so far in studies on chemosensory systems, and our knowledge mostly concerns the detection of airborne cues. A broader comparative approach is therefore desirable. Marine annelid worms with their rich behavioural repertoire represent attractive models for chemosensation. Here, we study the marine worm Platynereis dumerilii to provide the first comprehensive investigation of head chemosensory organ physiology in an annelid. By combining microfluidics and calcium imaging, we record neuronal activity in the entire head of early juveniles upon chemical stimulation. We find that Platynereis uses four types of organs to detect stimuli such as alcohols, esters, amino acids and sugars. Antennae are the main chemosensory organs, compared to the more differentially responding nuchal organs or palps. We report chemically evoked activity in possible downstream brain regions including the mushroom bodies (MBs), which are anatomically and molecularly similar to insect MBs. We conclude that chemosensation is a major sensory modality for marine annelids and propose early Platynereis juveniles as a model to study annelid chemosensory systems.

The Chemical Sensitivity and Electrical Activity of Individual Olfactory Sensory Neurons to a Range of Sex Pheromones and Food Odors in the Goldfish

Although it is well established that the olfactory epithelium of teleost fish detects at least 6 classes of biologically relevant odorants using 5 types of olfactory sensory neurons (OSNs), little is understood about the specificity of individual OSNs and thus how they encode identity of natural odors. In this study, we used in vivo extracellular single-unit recording to examine the odor responsiveness and physiological characteristics of 109 individual OSNs in mature male goldfish to a broad range of biological odorants including feeding stimuli (amino acids, polyamines, nucleotides), sex pheromones (sex steroids, prostaglandins [PGs]), and a putative social cue (bile acids). Sixty-one OSNs were chemosensitive, with over half of these (36) responding to amino acids, 7 to polyamines, 7 to nucleotides, 5 to bile acids, 9 to PGs, and 7 to sex steroids. Approximately a quarter of the amino acid-sensitive units also responded to polyamines or nucleotides. Three of 6 amino acid-sensitive units responded to more than 1 amino acid compound, and 5 sex pheromone-sensitive units detected just 1 sex pheromone. While pheromone-sensitive OSNs also responded to the adenylyl cyclase activator, forskolin, amino acid-sensitive OSNs responded to either forskolin or a phospholipase C activator, imipramine. Most OSNs responded to odorants and activators with excitation. Our results suggest that pheromone information is encoded by OSNs specifically tuned to single sex pheromones and employ adenylyl cyclase, suggestive of a labeled-line organization, while food information is encoded by a combination of OSNs that use both adenylyl cyclase and phospholipase C and are often less specifically tuned.

Crayfish can distinguish between natural and chemical stimuli as assessed by cardiac and locomotor reactions

In this study, cardiac and locomotor activities of signal crayfish Pacifastacus leniusculus were investigated under exposure to a range of natural (i.e., odors of conspecific crayfish, predatory fish, food, and injured conspecific) and one chemical (i.e., disinfectant chloramine-T) stimuli. Crayfish locomotion was simultaneously initiated with an increase in heart rate only when affected by chloramine-T, while locomotor response was delayed in all cases (or was not manifested at all by some specimens) when disturbed by the natural stressors. The heart rate differences measured before and during the stimulation were arranged as follows: odor of conspecific crayfish (9.2 ± 7.1%) < predator (18.4 ± 13%) < food (33.5 ± 15.7%) < chloramine-T (41.1 ± 14.7%) < injured conspecific (51.8 ± 28.4%). Analysis of the peculiarities of crayfish heartbeat under exposure to the tested stimuli revealed complex cardiac responses as was previously observed by an electrocardiography approach, that is, a slowed heart rate followed by a delayed increase. Evaluation of the intrinsic parameters of crayfish bioindicators remains essential due to the possibility of detection of the substantial ethological responses even in motionless animals. The role and appropriateness of signal crayfish as a bioindicator of water quality is discussed; they seem to be an applicable species for this task due to their sufficient sensitivity and broad availability. In addition to providing a better understanding of stereotypic crayfish behaviors induced by common and chemical stressors, the results of this study may serve as reference data for the evaluation of crayfish suitability for water quality tests.

Algae associated with coral degradation affects risk assessment in coral reef fishes

Habitat degradation alters the chemical landscape through which information about community dynamics is transmitted. Olfactory information is crucial for risk assessment in aquatic organisms as predators release odours when they capture prey that lead to an alarm response in conspecific prey. Recent studies show some coral reef fishes are unable to use alarm odours when surrounded by dead-degraded coral. Our study examines the spatial and temporal dynamics of this alarm odour-nullifying effect, and which substratum types may be responsible. Field experiments showed that settlement-stage damselfish were not able to detect alarm odours within 2 m downcurrent of degraded coral, and that the antipredator response was re-established 20-40 min after transferral to live coral. Laboratory experiments indicate that the chemicals from common components of the degraded habitats, the cyanobacteria, Okeania sp., and diatom, Pseudo-nitzschia sp.prevented an alarm odour response. The same nullifying effect was found for the common red algae, Galaxauria robusta, suggesting that the problem is of a broader nature than previously realised. Those fish species best able to compensate for a lack of olfactory risk information at key times will be those potentially most resilient to the effects of coral degradation that operate through this mechanism.

Crustacean olfactory systems: A comparative review and a crustacean perspective on olfaction in insects

Malacostracan crustaceans display a large diversity of sizes, morphs and life styles. However, only a few representatives of decapod taxa have served as models for analyzing crustacean olfaction, such as crayfish and spiny lobsters. Crustaceans bear multiple parallel chemosensory pathways represented by different populations of unimodal chemosensory and bimodal chemo- and mechanosensory sensilla on the mouthparts, the walking limbs and primarily on their two pairs of antennae. Here, we focus on the olfactory pathway associated with the unimodal chemosensory sensilla on the first antennal pair, the aesthetascs. We explore the diverse arrangement of these sensilla across malacostracan taxa and point out evolutionary transformations which occurred in the central olfactory pathway. We discuss the evolution of chemoreceptor proteins, comparative aspects of active chemoreception and the temporal resolution of crustacean olfactory system. Viewing the evolution of crustacean brains in light of energetic constraints can help us understand their functional morphology and suggests that in various crustacean lineages, the brains were simplified convergently because of metabolic limitations. Comparing the wiring of afferents, interneurons and output neurons within the olfactory glomeruli suggests a deep homology of insect and crustacean olfactory systems. However, both taxa followed distinct lineages during the evolutionary elaboration of their olfactory systems. A comparison with insects suggests their olfactory systems ö especially that of the vinegar fly ö to be superb examples for "economy of design". Such a comparison also inspires new thoughts about olfactory coding and the functioning of malacostracan olfactory systems in general.

Sensory evolution in blind cavefish is driven by early embryonic events during gastrulation and neurulation

Natural variations in sensory systems constitute adaptive responses to the environment. Here, we compared sensory placode development in the blind cave-adapted morph and the eyed river-dwelling morph of Astyanax mexicanus Focusing on the lens and olfactory placodes, we found a trade-off between these two sensory components in the two morphs: from neural plate stage onwards, cavefish have larger olfactory placodes and smaller lens placodes. In a search for developmental mechanisms underlying cavefish sensory evolution, we analyzed the roles of Shh, Fgf8 and Bmp4 signaling, which are known to be fundamental in patterning the vertebrate head and are subtly modulated in space and time during cavefish embryogenesis. Modulating these signaling systems at the end of gastrulation shifted the balance toward a larger olfactory derivative. Olfactory tests to assess potential behavioral outcomes of such developmental evolution revealed that Astyanax cavefish are able to respond to a 10⁵-fold lower concentration of amino acids than their surface-dwelling counterparts. We suggest that similar evolutionary developmental mechanisms may be used throughout vertebrates to drive adaptive sensory specializations according to lifestyle and habitat.

Mechanisms underlying the control of responses to predator odours in aquatic prey

In aquatic systems, chemical cues are a major source of information through which animals are able to assess the current state of their environment to gain information about local predation risk. Prey use chemicals released by predators (including cues from a predator's diet) and other prey (such as alarm cues and disturbance cues) to mediate a range of behavioural, morphological and life-history antipredator defences. Despite the wealth of knowledge on the ecology of antipredator defences, we know surprisingly little about the physiological mechanisms that control the expression of these defensive traits. Here, we summarise the current literature on the mechanisms known to specifically mediate responses to predator odours, including dietary cues. Interestingly, these studies suggest that independent pathways may control predator-specific responses, highlighting the need for greater focus on predator-derived cues when looking at the mechanistic control of responses. Thus, we urge researchers to tease apart the effects of predator-specific cues (i.e. chemicals representing a predator's identity) from those of diet-mediated cues (i.e. chemicals released from a predator's diet), which are known to mediate different ecological endpoints. Finally, we suggest some key areas of research that would greatly benefit from a more mechanistic approach.

Antennular Morphology and Contribution of Aesthetascs in the Detection of Food-related Compounds in the Shrimp Palaemon adspersus Rathke, 1837 (Decapoda: Palaemonidae)

Shrimp are an essential ecological component of marine ecosystems, and have commercial importance for human consumption and aquaculture. Like other decapod crustaceans, shrimp rely on chemical senses to detect and localize food resources by means of chemosensilla that are located mainly on the cephalothoracic appendages. Using the shrimp Palaemon adspersus, a model organism with omnivorous feeding behavior, we aimed to provide comparative information on the role of aesthetascs, antennular sensilla, and flicking behavior in food detection. To this end, we examined i) the morphology of antennular sensilla by field emission scanning electron microscopy, ii) the shrimp's sensitivity to a number of food-related compounds (amino acids and sugars) by means of whole-animal bioassays, and iii) the contribution of the aesthetasc sensilla to food detection. Our results showed that, aside from the aesthetascs, only three other main morphotypes of setae with chemoreceptive features were present in the antennules, thus accounting for relatively simple sensillar equipment. Nevertheless, we found broad-spectrum sensitivity of the shrimp to a number of amino acids (i.e., isoleucine, leucine, methionine, phenylalanine, glycine, tryptophan, cysteine, and tyrosine) and carbohydrates (trehalose, maltose, cellobiose, and fructose) that was consistent with the omnivorous or scavenging habits of the animal. Although aesthetasc ablation attenuated flicking behavior in a chemical stimulus-independent manner, success in detection and short-range localization of food did not rely on the presence of aesthetasc sensilla. This finding confirms the existence of a non-aesthetasc alternative pathway for feeding, with functional redundancy in simple generalist feeder models such as shrimp.

Chemical Cues which Include Amino Acids Mediate Species-Specific Feeding Behavior in Invasive Filter-Feeding Bigheaded Carps

This study tested whether and how dissolved chemicals might assist food recognition in two filter-feeding fishes, the silver (Hypophthalmichthys molitrix) and the bighead carp (H. nobilis). These species evolved in Asia, are now invasive in the Mississippi River, and feed voraciously on microparticles including plankton. The food habits and biology of these carps are broadly similar to many filter-feeding fish, none of whose chemical ecology has been examined. We conducted five experiments. First, we demonstrated that buccal-pharngeal pumping (BPP), a behavior in which fish pump water into their buccal cavities, is responsible for sampling food: BPP activity in both silver and bighead carps was low and increased nearly 25-fold after exposure to a filtrate of a planktonic food mixture (P < 0.01) and over 35-fold when planktonic food was added (P < 0.001). Next, we showed that of nine food filtrates, the one containing chemicals released by spirulina, a type of cyanobacterium, was the most potent planktonic component for both species. The potency of filtrates varied between species in ways that reflected their different chemical compositions. While L-amino acids could explain about half of the activity of food filtrate, other unknown chemical stimuli were also implicated. Finally, occlusion experiments showed the olfactory sense has a very important, but not exclusive, role in bigheaded carp feeding behaviors and this might be exploited in both their control and culture.