Effects of a chronic exposure to different water temperatures and/or to an environmental cadmium concentration on the reproduction of the threespine stickleback (Gasterosteus aculeatus)

The Direct Effects of Climate Change on Tench (Tinca tinca) Sperm Quality under a Real Heatwave Event Scenario

Global aquaculture growth will most probably face specific conditions derived from climate change. In fact, the most severe impacts of these changes will be suffered by aquatic populations in restrictive circumstances, such as current aquaculture locations, which represent a perfect model to study global warming effects. Although the impact of temperature on fish reproduction has been characterized in many aspects, this study was focused on recreating more realistic models of global warming, particularly considering heatwave phenomena, in order to decipher its effects on male gametes (spermatozoa). For this purpose, thermal stress via a heatwave simulation (mimicking a natural occurring heatwave, from 24 to 30 °C) was induced in adult tench (Tinca tinca) males and compared with a control group (55.02 ± 16.44 g of average body wet weight). The impact of the thermal stress induced by this climate change event was assessed using cellular and molecular approaches. After the heatwave recreation, a multiparametric analysis of sperm quality, including some traditional parameters (such as sperm motility) and new ones (focus on redox balance and sperm quality biomarkers), was performed. Although sperm concentration and the volume produced were not affected, the results showed a significant deleterious effect on motility parameters (e.g., reduced progressive motility and total motility during the first minute post-activation). Furthermore, the sperm produced under the thermal stress induced by this heatwave simulation exhibited an increased ROS content in spermatic cells, confirming the negative effect that this thermal stress model (heatwave recreation) might have had on sperm quality. More importantly, the expression of some known sperm quality and fertilization markers was decreased in males exposed to thermal stress. This present study not only unveils the potential effects of climate change in contemporary and future fish farming populations (and their underlying mechanisms) but also provides insights on how to mitigate and/or avoid thermal stress due to heatwave events.

Fluctuating and Stable High Temperatures Differentially Affect Reproductive Endocrinology of Female Pupfish

For many fishes, reproductive function is thermally constrained such that exposure to temperatures above some upper threshold has detrimental effects on gametic development and maturation, spawning frequency, and mating behavior. Such impairment of reproductive performance at elevated temperatures involves changes to hypothalamic-pituitary-gonadal (HPG) axis signaling and diminished gonadal steroidogenesis. However, how HPG pathways respond to consistently high versus temporally elevated temperatures is not clear. Here, sexually mature Amargosa River Pupfish (Cyprinodon nevadensis amargosae) were maintained under thermal regimes of either stable ∼25°C (low temperature), diurnal cycling temperatures between ∼27 and 35°C (fluctuating temperature), or stable ∼35°C (high temperature) conditions for 50 days to examine effects of these conditions on HPG endocrine signaling components in the pituitary gland and gonad, ovarian and testicular gametogenesis status, and liver gene expression relating to oogenesis. Female pupfish maintained under stable high and fluctuating temperature treatments showed reduced gonadosomatic index values as well as a lower proportion of oocytes in the lipid droplet and vitellogenic stages. Females in both fluctuating and stable 35°C conditions exhibited reduced ovarian mRNAs for steroid acute regulatory protein (star), cholesterol side chain-cleavage enzyme, P450scc (cyp11a1), and 3β-hydroxysteroid dehydrogenase (3bhsd), while ovarian transcripts encoding 11β-hydroxysteroid dehydrogenase (11bhsd) and sex hormone-binding globulin (shbg) were elevated in females at constant 35°C only. Ovarian aromatase (cyp19a1a) mRNA levels were unaffected, but circulating 17β-estradiol (E2) was lower in females at 35°C compared to the fluctuating temperature condition. In the liver, mRNA levels for choriogenins and vitellogenin were downregulated in both the fluctuating and 35°C conditions, while hepatic estrogen receptor 2a (esr2a) and shbg mRNAs were elevated in 35°C females. Taken together, these results demonstrate the potential for elevated temperatures to impair ovarian steroidogenesis and reduce egg envelope and vitellogenin protein production in female C. n. amargosae pupfish, while also shedding light on how thermal regimes that only intermittently reach the upper thermal range for reproduction have differential impacts on reproductive endocrine pathways than constantly warm conditions.

Sexually mediated phenotypic variation within and between sexes as a continuum structured by ecology: The mosaic nature of skeletal variation across body regions in Threespine stickleback (Gasterosteus aculeatus L.)

Ecological character displacement between the sexes, and sexual selection, integrate into a convergent set of factors that produce sexual variation. Ecologically modulated, sexually mediated variation within and between sexes may be a major contributor to the amount of total variation that selection can act on in species. Threespine stickleback (Gasterosteus aculeatus) display rapid adaptive responses and sexual variation in many phenotypic traits. We examined phenotypic variation in the skull, pectoral and pelvic girdles of threespine stickleback from two freshwater and two coastal marine sites on the Sunshine Coast of British Columbia, Canada, using an approach that avoids a priori assumptions about bimodal patterns of variation. We quantified shape and size of the cranial, pectoral and pelvic regions of sticklebacks in marine and freshwater habitats using 3D geometric morphometrics and an index of sexually mediated variation. We show that the expression of phenotypic variation is structured in part by the effects of both habitat marine vs freshwater and the effects of individual sites within each habitat. Relative size exerts variable influence, and patterns of phenotypic variation associated with sex vary among body regions. This fine-grained quantification of sexually mediated variation in the context of habitat difference and different anatomical structures indicates a complex relationship between genetically inferred sex and environmental factors, demonstrating that the interplay between shared genetic background and sexually mediated, ecologically based selective pressures structures the phenotypic expression of complex traits.

Accustomed to the heat: Temperature and thyroid hormone influences on oogenesis and gonadal steroidogenesis pathways vary among populations of Amargosa pupfish (Cyprinodon nevadensis amargosae)

Many fish experience diminished reproductive performance under atypically high or prolonged elevations of temperature. Such high temperature inhibition of reproduction comes about in part from altered stimulation of gametogenesis by the hypothalamic-pituitary-gonadal (HPG) endocrine axis. Elevated temperatures have also been shown to affect thyroid hormone (TH) signaling, and altered TH status under high temperatures may impact gametogenesis via crosstalk with HPG axis pathways. Here, we examined effects of temperature and 3'-triiodo-_L-thyronine (T₃) on pathways for gonadal steroidogenesis and gametogenesis in Amargosa pupfish (Cyprinodon nevadensis amargosae) from two allopatric populations: 1) the Amargosa River - a highly variable temperature habitat, and 2) Tecopa Bore - an invariably warm groundwater-fed marsh. These populations were previously shown to differ in TH signaling profiles both in the wild and under common laboratory conditions. Sexually-mature pupfish from each population were maintained at 24 °C or 34 °C for 88 days, after which a subset of fish was treated with T₃ for 18-24 h. In both populations, mRNA abundances for follicle-stimulating hormone receptor and luteinizing hormone receptor were higher in the ovary and testis at 24 °C compared to 34 °C. Females from Tecopa Bore - but not from the Amargosa River - also had greater ovarian transcript abundances for steroidogenic enzymes cytochrome P450 aromatase, 3β-hydroxysteroid dehydrogenase, and 17β-hydroxysteroid dehydrogenase at 24 °C compared to 34 °C, as well as higher liver mRNA levels of vitellogenins and choriogenins at cooler temperature. Transcript abundances for estrogen receptors esr1, esr2a, and esr2b were reduced at 34 °C in Amargosa River females, but not in Tecopa Bore females. T₃ augmented gonadal gene transcript levels for steroid acute regulatory protein (StAR) transporter in both sexes and populations. T₃ also downregulated liver estrogen receptor mRNAs in females from the warmer Tecopa Bore habitat only, suggesting T₃ modulation of liver E₂ sensitivity as a possible mechanism whereby temperature-induced changes in TH status may contribute to shifts in thermal sensitivity for oogenesis.

Interactions effects of nano-microplastics and heavy metals in hybrid snakehead (Channa maculata ♀ × Channa argus ♂)

The interaction between microplastics and contaminants has potentially generated new undefined risks on animals and ecosystems, and nano-microplastics are considered to be more harmful than microplastics. This experiment investigated the interactions and effects of nano-microplastics with heavy metals cadmium in hybrid snakehead. Different concentrations of nano-microplastics 80 nm (50 μg/L and 500 μg/L) and Cd (50 μg/L) were used for exposure, and four sampling points were set for 24 h, 48 h, 96 h and clear-48 h. Results indicated that the morphology of gill was altered under the influence of nano-microplastics and cadmium, and the damage was aggravated with time. Nano-microplastics and Cd can cause oxidative damage to fish liver partly by effect the activities of antioxidant enzyme, and significantly suppressed the expressions of genes related to the inflammation (IL-1β and TNF-α) and as well as significantly up-regulated the expression of genes HSP70 and SOD. Additionally, the mRNA levels of MT gene can be speculated that the heavy metal cadmium may accumulated in the body over time. And the concentration of heavy metals will also affect their accumulation in the body. Our study elucidated the nano-microplastics and Cd will increase the impact on environmental and organisms that the nano-microplastics contribute to the bioaccumulation of metals, which served as a new support for study the interaction between environmental contaminants.

Less impact than suspected: Dietary exposure of three-spined sticklebacks to microplastic fibers does not affect their body condition and immune parameters

Microplastic fibers are frequent anthropogenic contaminants in most aquatic environments and have consequently been detected in the digestive tract of many fish species. Upon ingestion, microplastic fibers pose risks of interference with nutrient uptake, impaired intestinal health, and as a consequence may alter growth performance and fitness. In addition, foreign particles such as fibers might cause tissue irritations and stress, and thus interfere with immune parameters. In nature, fish regularly encounter microplastic fibers as well as fiber debris from natural sources and materials. Thus, we wanted to test the potential impact of microplastic fibers on growth, organosomatic indices, and immune parameters of subadult fish and compare these to possible effects caused by natural fibers. We administered sticklebacks diets, which were supplemented with either polyester or cotton fibers (each at concentrations of 0.2 mg/g and 2 mg/g feed) or a control diet without fiber supplementation for nine weeks. Mortalities did not occur and sticklebacks grew equally well across treatments. Neither organosomatic indices nor immune parameters revealed significant differences between treatments. While natural differences between males and females were observed for some parameters, no treatment-related gender-specific effects were detected. Our results suggest that the dietary uptake of polyester fibers does not affect growth, body condition, gonad development, and immunity of sticklebacks - even at fiber concentrations higher than what can be encountered in the wild. Furthermore, virgin microplastic fibers do not seem to affect fish differently than fibers from natural origin. The present study implies that at least some species are resilient towards pollution with (virgin) microplastic fibers even at high concentrations.

Impacts of heavy metals on early development, growth and reproduction of fish - A review

Heavy metals pollution causes a threat to the aquatic environment and to its inhabitants when their concentrations exceed safe limits. Heavy metals cause toxicity in fish due to their non-biodegradable properties and their long persistence in the environment. This review investigated the effects of heavy metals on early development, growth and reproduction of fish. Fish embryos/larvae and each developmental stage of embryo respond differently to the intoxication and vary from species to species, types of metals and their mode of actions, concentration of heavy metals and their exposure time. Many of the heavy metals are considered as essential nutrient elements that positively improve the growth and feed utilization of fishes but upon crossing the maximum tolerable limit these metals cause not only a hazard to fish health but also to human consumers and the disruption of ecological systems. Reduced gonadosomatic index (GSI), fecundity, hatching rate, fertilization success, abnormal shape of reproductive organs, and finally failure of reproduction in fish have been attributed to heavy metal toxicity. In summary, this review sheds light on the manipulation of fish physiology by heavy metals and seeks to raise sensitivity to the prevention and control of aquatic environmental contamination, particularly from heavy metals.

Combined effects of heatwaves and micropollutants on freshwater ecosystems: Towards an integrated assessment of extreme events in multiple stressors research

Freshwater ecosystems are strongly influenced by weather extremes such as heatwaves (HWs), which are predicted to increase in frequency and magnitude in the future. In addition to these climate extremes, the freshwater realm is impacted by the exposure to various classes of chemicals emitted by anthropogenic activities. Currently, there is limited knowledge on how the combined exposure to HWs and chemicals affects the structure and functioning of freshwater ecosystems. Here, we review the available literature describing the single and combined effects of HWs and chemicals on different levels of biological organization, to obtain a holistic view of their potential interactive effects. We only found a few studies (13 out of the 61 studies included in this review) that investigated the biological effects of HWs in combination with chemical pollution. The reported interactive effects of HWs and chemicals varied largely not only within the different trophic levels but also depending on the studied endpoints for populations or individuals. Hence, owing also to the little number of studies available, no consistent interactive effects could be highlighted at any level of biological organization. Moreover, we found an imbalance towards single species and population experiments, with only five studies using a multitrophic approach. This results in a knowledge gap for relevant community and ecosystem level endpoints, which prevents the exploration of important indirect effects that can compromise food web stability. Moreover, this knowledge gap impairs the validity of chemical risk assessments and our ability to protect ecosystems. Finally, we highlight the urgency of integrating extreme events into multiple stressors studies and provide specific recommendations to guide further experimental research in this regard.

Swimming behaviour in two ecologically similar three-spined (Gasterosteus aculeatus L.) and nine-spined sticklebacks (Pungitius pungitius L.): a comparative approach for modelling the toxicity of metal mixtures

Sticklebacks (Gasterosteiformes) are increasingly used in ecological and evolutionary research and have become well established as role model species for biologists. However, ecotoxicology studies concerning behavioural effects in sticklebacks regarding stress responses, mainly induced by chemical mixtures, have hardly been addressed. For this purpose, we investigated the swimming behaviour (including mortality rate based on 96-h LC₅₀ values) of two ecologically similar three-spined (Gasterosteus aculeatus) and nine-spined sticklebacks (Pungitius pungitius) to short-term (up to 24 h) metal mixture (MIX) exposure. We evaluated the relevance and efficacy of behavioural responses of test species in the early toxicity assessment of chemical mixtures. Fish exposed to six (Zn, Pb, Cd, Cu, Ni, and Cr) metals in the mixture were either singled out by the Water Framework Directive as priority or as relevant substances in surface water, which was prepared according to the environmental quality standards (EQSs) of these metals set for inland waters in the European Union (EU) (Directive 2013/39/EU). The performed behavioural analysis showed the main effect on the interaction between time, species, and treatment variables. Although both species exposed to MIX revealed a decreasing tendency in swimming activity, these species' responsiveness to MIX was somewhat different. Substantial changes in the activity of G. aculeatus were established after a 3-h exposure to MIX solutions, which was 1.43-fold lower, while in the case of P. pungitius, 1.96-fold higher than established 96-h LC₅₀ values for each species. This study demonstrated species-specific differences in response sensitivity to metal-based water pollution, indicating behavioural insensitivity of P. pungitius as model species for aquatic biomonitoring and environmental risk assessments.

Evaluation of the combined effect of elevated temperature and cadmium toxicity on Daphnia magna using a simplified DEBtox model

Thermal discharge and heatwaves under climate change may increase water temperature. In this study, the individual and combined effect of elevated temperature and cadmium (Cd) toxicity on somatic growth and reproduction of Daphnia magna was evaluated using a simplified dynamic energy budget model (DEBtox). The model predicted that the maximum body length (L_m) would be shorter (3.705 mm) at an elevated temperature of 25 °C than at 20 °C (3.974 mm), whereas the maximum reproduction rate (R˙_m) would be higher at 25 °C (5.735) than at 20 °C (5.591). The somatic growth and reproduction of D. magna were significantly (p < 0.05) reduced with increasing Cd concentrations, and the reduction was greater at 25 than at 20 °C. Potentiation of Cd toxicity by elevated temperature was correctly simulated by assuming four toxicological modes of action influencing assimilation, somatic maintenance and growth, and reproduction. Overall, the population growth rate of D. magna was expected to decrease linearly with increasing Cd concentrations, and the decrease was expected to be higher at 25 than at 20 °C. These findings suggest a significant ecological risk of toxic metals at elevated temperature, with a mechanistic interpretation of the potentiation effect using a DEBtox modeling approach.

Effects of continuous and intermittent cadmium exposure on HPGL axis, GH/IGF axis and circadian rhythm signaling and their consequences on reproduction in female zebrafish: Biomarkers independent of exposure regimes

Typical biomarkers of cadmium (Cd) pollution have well been confirmed in fish from continuous exposure pattern. However, in a natural environment, fish may be exposed to Cd intermittently. In this study, juvenile female zebrafish were exposed for 48 days to 10 μg/L Cd continuously, 20 μg/L for 1 day in every 2 days or 30 μg/L for 1 day in every 3 days. The toxic effects were evaluated using 8 various physiological and biochemical endpoints like specific growth rate (SGR), 17β-estradiol (E2) and vitellogenin (VTG) concentrations in plasma, reproductive parameters (gonadosomatic index (GSI), egg-laying amount, spawning percentage, and hatching and mortality rate of embryos). Transcription of 59 genes related to hypothalamic-pituitary-gonadal-liver (HPGL) axis, circadian rhythm signaling and insulin-like growth factor (IGF) system was examined. SGR, spawning percentage, E2 and VTG levels declined in fish exposed to 10 and 20 μg/L Cd but remained relatively stable in fish exposed to 30 μg/L Cd. Exposure to 10, 20 and 30 μg/L Cd significantly reduced GSI, hatching rate and mortality rate. Similarly, mRNA expression of 27 genes were sensitive to both continuous and intermittent Cd exposure. Among these genes, expression levels of 10 genes had more than 5-fold increase or decrease, including mRNA levels of vtg1, vtg2, vtg3, esr1, igf2a, igf2b, igfbp5b, nr1d1, gnrh3 and gnrhr4. The most sensitive molecular biomarker was vtg3 expression with 1500-3100 fold increase in the liver. The present study, for the first time, provides effective candidate biomarkers for Cd, which are independent of exposure regimes.

miR-217 through SIRT1 regulates the immunotoxicity of cadmium in Cyprinus carpio

MicroRNAs (miRNAs) play a critical role in regulating the response of animals exposed to heavy metal stress. As a globally dispersed heavy metal in aquatic ecosystems, cadmium (Cd) is highly toxic to many aquatic species. However, little is known about the miRNA response to Cd stress in fish. To investigate the regulatory effect of miRNAs in response to Cd, common carp (Cyprinus carpio) were exposed to Cd²⁺-containing water (0.005 mg/L, 0.05 mg/L, 0.5 mg/L) for 30 days. After exposure, Cd²⁺ contents were significantly higher in the kidneys of C. carpio compared to other tissues, when exposed to 0.5 mg/L Cd²⁺. Hematoxylin and eosin staining images revealed that elevated Cd induced inflammatory damage in the kidneys of C.carpio. Further, miRNA sequencing revealed nine differentially expressed miRNAs (miR-217, miR-205 and seven novel miRNAs) in the kidneys, between 0.5 mg/L Cd²⁺ exposure and control groups. Potential target mRNAs of miRNAs suggest that miR-217 is involved in immunotoxicity. miR-217 agomir was intraperitoneally administered to C. carpio and RT-PCR revealed that the expression of IL-8 and SIRT1 decreased, while TLR-4, TRAF6, NF-kB, TNF-α, IL-1β, and TGF-β increased in the kidneys of C.carpio. Additionally, the expression of SIRT1 decreased, while the expression of other mRNAs increased in kidneys of C. carpio exposed to Cd. According to mRNAs expression in the agomir and Cd treatment, miRNAs inhibit the expressions of target mRNAs. These results demonstrate that miR-217 via SIRT1 plays a regulatory role in the immunotoxicity of Cd to C. carpio.

Changes in Cadmium Concentration in Muscles, Ovaries, and Eggs of Silver European Eel (Anguilla anguilla) during Maturation under Controlled Conditions

This study determined the contents of cadmium (Cd) in the muscles, ovaries, and eggs of silver female European eels. The analysis of cadmium content was performed on female European eels caught during commercial fishing in freshwater in Warmia and Mazury (Poland), and then subjected to artificial maturation and ovulation processing under controlled conditions. The content of cadmium (Cd) in the tissues was determined by flameless atomic spectrometry using an electrothermal atomizer. The analysis showed statistically significant differences between the cadmium content in the muscles, ovaries, and eggs (p < 0.05) of female European eels. The lowest cadmium content was found in the muscle tissue (0.0012 ± 0.0001 mg kg-1 wet weight) and the highest in eggs (after ovulation) (0.0038 ± 0.0007 mg kg-1 wet weight). Moreover, a relationship was found between the cadmium content in the muscle tissue and the ovaries (R = 0.673; p = 0.0117) in the same fish. The movement of cadmium from tissues to oocytes may indicate a significant problem concerning this heavy metal content in the reproduction of European eel.

FifBase: a comprehensive fertility-associated indicators factor database for domestic animals

Fertility refers to the ability of animals to maintain reproductive function and give birth to offspring, which is an important indicator to measure the productivity of animals. Fertility is affected by many factors, among which environmental factors may also play key roles. During the past years, substantial research studies have been conducted to detect the factors related to fecundity, including genetic factors and environmental factors. However, the identified genes associated with fertility from countless previous studies are randomly dispersed in the literature, whereas some other novel fertility-related genes are needed to detect from omics-based datasets. Here, we constructed a fertility index factor database FifBase based on manually curated published literature and RNA-Seq datasets. During the construction of the literature group, we obtained 3301 articles related to fecundity for 13 species from PubMed, involving 2823 genes, which are related to 75 fecundity indicators or 47 environmental factors. Eventually, 1558 genes associated with fertility were filtered in 10 species, of which 1088 and 470 were from RNA-Seq datasets and text mining data, respectively, involving 2910 fertility-gene pairs and 58 fertility-environmental factors. All these data were cataloged into FifBase (http://www.nwsuaflmz.com/FifBase/), where the fertility-related factor information, including gene annotation and environmental factors, can be browsed, retrieved and downloaded with the user-friendly interface.

Bisphenol S exposure alters behavioral parameters in adult zebrafish and offspring

The environmental emission of bisphenol S (BPS), which is globally utilized in the manufacturing of polycarbonates, epoxy resin and thermal paper, has affected the aquatic ecosystem. Thus, effects of BPS exposure on the fitness of aquatic animals have been noted. Here, adult male and female zebrafish were used as aquatic model organisms and separately exposed to environmentally relevant doses of BPS (0, 1, 10 and 100 μg/L) for 14 days. The results showed that BPS changed the body pigment of zebrafish and slowed the maturation of oocytes in the ovary, resulting in a significant decrease in the shoaling behavior of adult zebrafish and the attraction of BPS-treated females during the mating process. Furthermore, in the subgeneration of adult zebrafish exposed to BPS for 7 days, survival behaviors, such as locomotor, phototaxis and feeding behaviors, deviated from normal behaviors. After exposing the adult zebrafish to BPS for an additional 7 days, the above described survival behaviors and light adaptation were disrupted in offspring. Our data, based on intergenerational behavioral studies, demonstrate that BPS affects the behaviors of aquatic animals and the ability of offspring to feed and avoid predators, possibly jeopardizing the survival of aquatic animals.

From gametogenesis to spawning: How climate-driven warming affects teleost reproductive biology

Ambient temperature modulates reproductive processes, especially in poikilotherms such as teleosts. Consequently, global warming is expected to impact the reproductive function of fish, which has implications for wild population dynamics, fisheries and aquaculture. In this extensive review spanning tropical and cold-water environments, we examine the impact of higher-than-optimal temperatures on teleost reproductive development and physiology across reproductive stages, species, generations and sexes. In doing so, we demonstrate that warmer-than-optimal temperatures can affect every stage of reproductive development from puberty through to the act of spawning, and these responses are mediated by age at spawning and are associated with changes in physiology at multiple levels of the brain-pituitary-gonad axis. Response to temperature is often species-specific and changes with environmental history/transgenerational conditioning, and the amplitude, timing and duration of thermal exposure within a generation. Thermally driven changes to physiology, gamete development and maturation typically culminate in poor sperm and oocyte quality, and/or advancement/delay/inhibition of ovulation/spermiation and spawning. Although the field of teleost reproduction and temperature is advanced in many respects, we identify areas where research is lacking, especially for males and egg quality from "omics" perspectives. Climate-driven warming will continue to disturb teleost reproductive performance and therefore guide future research, especially in the emerging areas of transgenerational acclimation and epigenetic studies, which will help to understand and project climate change impacts on wild populations and could also have implications for aquaculture.

Temperature and concentration of ZnO particles affect life history traits and oxidative stress in Daphnia magna

Temperature affects physiological processes in organisms and the toxicity of chemicals. The widespread industrial use of ZnO causes contamination in aquatic ecosystems. This study aimed to investigate the chronic toxicity of ZnO at different temperatures using Daphnia magna as a model organism. The chronic toxicity of five different concentrations of ZnO was assessed at 23 °C and 28 °C. The results showed that higher concentrations of ZnO inhibited growth, production of first clutch eggs and juvenile accumulation at both 23 °C and 28 °C. Growth rate, numbers of first clutch eggs and juvenile accumulation were lower at 28 °C than at 23 °C. We also observed the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) activity. At higher concentrations of ZnO, oxidative stress was induced leading to increase MDA level and decrease SOD activity at 28 °C. These findings indicated that high temperature and high concentration of ZnO inhibited the activity of enzymatic proteins. Nonetheless, among all treatments, the accumulation of zinc in D. magna was not significantly different. Our results suggested that both ZnO and higher temperature induced oxidative stress in D. magna. As a result, MDA concentration increased, SOD activity changed and the growth and reproduction of D. magna was adversely affected.

Neurotoxicity, Behavior, and Lethal Effects of Cadmium, Microplastics, and Their Mixtures on Pomatoschistus microps Juveniles from Two Wild Populations Exposed under Laboratory Conditions-Implications to Environmental and Human Risk Assessment

Microplastics (MPs) were found to modulate the toxicity of other pollutants but the knowledge on the topic is still limited. The goals of this study were to investigate the short-term toxicity of cadmium (Cd) to wild Pomatochistus microps juveniles, the potential modulation of acute Cd toxicity by 1–5 µm polyethylene MPs in this species, and possible differences of sensitivity to Cd and MPs-Cd mixtures between juveniles from two distinct wild populations. Juveniles were collected in the estuaries of Minho (M-est) and Lima (L-est) Rivers (NW Portugal). One 96 h bioassay with M-est juveniles and another one with L-est juveniles were carried out in laboratory conditions. Each bioassay had 12 treatments: control, 5 Cd concentrations, 1 MPs concentration, and 5 MPs-Cd mixtures. No significant differences in Cd-induced mortality between juveniles from distinct estuaries or between juveniles exposed to Cd alone and those exposed to MPs-Cd mixtures were found. The total 96h LC₁₀ and LC₅₀ of Cd alone were 2 mg/L (95% CI: 0–4 mg/L) and 8 mg/L (95% CI: 2–17 mg/L), respectively. Cd alone significantly decreased the post-exposure predatory performance (PEPP) of M-est (≥6 mg/L) and L-est juveniles (≥3 mg/L), and acetylcholinesterase (AChE) activity of M-est juveniles (13 mg/L). MPs alone (0.14 mg/L) significantly reduced the PEPP and AChE activity of L-est juveniles but not of M-est juveniles. MPs-Cd mixtures (3–13 mg/L of Cd + 0.14 mg/L of MPs) significantly inhibited the PEPP of juveniles from both estuaries and AChE of L-est estuary juveniles but not of M-est juveniles. Evidences of toxicological interactions, namely antagonism, between MPs and Cd were found. Overall, the results indicate that MPs modulated the sub-lethal toxic effects of Cd in wild P. microps juveniles, especially neurotoxicity. Moreover, the environmental conditions of the natural habitats to which juveniles were exposed during pre-developmental phases influence the sub-lethal toxicity of Cd, MPs, and their mixtures. The implications to environmental and human risk assessment are discussed and further research is needed.