Novel methodologies in marine fish larval nutrition

Optimization of Selenium Inclusion Level in the Larval Diet of Labeo rohita

The nutritional requirement of fish larvae remains a limiting factor in advanced aquaculture. Micronutrients are crucial for early development, but their dietary inclusion level in the larval feed of carps has not been standardized. The present study was executed to determine the optimum dietary inclusion level of organic and inorganic selenium in the larval feed of Rohu, Labeo rohita. A 35-day feeding trial in triplicate under semi-control conditions was conducted in 21 troughs divided into seven groups. Each trough (capacity 4.0 L) contained 200 larvae (average body weight 0.4 mg). The first group (control) was reared on nano-particulate basal diet (CP 50%), while three groups Se-Na(0.5), Se-Na(1), and Se-Na(1.5) were fed basal diet supplemented with graded levels (0.5-1.5 mg/kg diet) of inorganic form of Se, sodium selenite (Se-Na). The last three groups (Se-Met(0.5), Se-Met(1), and Se-Met(1.5)) were fed organic form of dietary Se, selenium methionine (Se-Met) at the same inclusion level as Se-Na. Results indicated the curvilinear relationship of dietary Se levels with body weight, activity of digestive enzymes (protease, amylase, lipases, and trypsin), and antioxidant enzymes (SOD, CAT, POD, and GSH-Px) activity, intestinal villi, width, and absorptive area. A positive correlation was observed with up to 0.5 and 1 mg/kg diet of Se-Na and Se-Met, respectively; however, above these levels, a negative impact was observed. The upregulation of growth hormone mediator (IGF-1) and downregulation of heat shock protein (HSP-70) also followed a similar trend in response to Se-Na and Se-Met inclusion. Based on the results, 1 mg/kg diet Se-Met could be considered the optimum level and is recommended for the early rearing of rohu larvae.

Optimization of inclusion level of lipid in larval diet of Labeo rohita (Hamilton, 1822)

Formulation and preparation of larval feed according to the requirement of Indian major carp is a prerequisite for improving the survival (%) and growth during early developmental stages. A feeding trial of 50 days in a replicate of five was conducted to determine the optimal inclusion levels of fish oil (lipid) in the larval diet of Labeo rohita. Four isonitrogenous (50% CP) nanoparticulate diets with four lipid inclusion levels, L5 (5%), L7 (7%), L9 (9%), and L11 (11%) were prepared and fed to four groups of rohu (Labeo rohita) larvae. At the end of feeding trial, survival (%), growth performance, digestive enzyme activity, gut morphology, and expression of growth and feed intake genes were evaluated. All pairwise comparisons among groups indicated higher growth performance (weight gain, specific growth rate, and daily weight gain), survival (%), and IGF-1 gene expression of the L9 group followed by the L7 while the L11 showed poor performance even less than L5. All studied intestinal enzymes except amylase showed a similar trend. Amylase showed comparable results among L7, L9, and L5, while L11 showed the lowest value. The intestinal villi length also showed higher values in L9 followed by L7, and lowest in the L11 group. Feed intake regulating genes, leptin showed lipid inclusion level upregulation, while ghrelin showed the highest expression in the L9 group. Based on growth performance, gut morphology, intestinal enzyme activity, and gene expression analysis, 9% dietary lipid could be recommended to ensure the optimum growth and survival of L. rohita larvae.

Assessing microplastic as a vector for chemical entry into fish larvae using a novel tube-feeding approach

A tube-feeding model for administering microplastic (MP, Ø = 30 μm) spheres to fish larvae was employed to quantify the uptake of hydrophobic organic contaminants (HOCs) into the larval body through a single administration of MP. Polychlorinated biphenyl-153 (PCB-153) was used as a representative HOC that can be sorbed to MP in the sea. Atlantic herring (Clupea harengus) larvae (34-51 days post-hatching) were selected as the animal model. The herring larvae were tube-fed a single load of up to 200 polystyrene or polyethylene MP spheres spiked with ¹⁴C-labelled PCB-153, and the control larvae were tube-fed an isotonic solution without MP. At the time of sampling (24 h post feeding), some larvae had evacuated all MP spheres from the gut, while others still had MP remaining in the gut. In larvae with a significant number of MP spheres still present in the gut, whole-body scintillation counting (including the MP in the gut lumen) showed elevated levels of the tracer compared to those in the control fish larvae. For larvae in which all or almost all MP had been evacuated by the time of sampling, the tracer levels of the whole body were not significantly different compared to those for the control fish larvae. These data indicate that there was no significant transfer of PCB-153 from contaminated MP into fish larvae within a gut-transit time of <24 h. This study suggests that the vector role of MP in HOC uptake and absorption may be minor compared to that of other HOC uptake pathways.

Skeletal Anomalies in Senegalese Sole (Solea senegalensis, Kaup) Fed with Different Commercial Enriched Artemia: A Study in Postlarvae and Juveniles

Simple Summary

Enrichment products for Artemia spp. metanauplii are commonly used to enhance the nutritional quality of this live prey offered to fish during conventional larval feeding. However, there are few reports on the influence of such enrichments on the development of skeletal anomalies in Senegalese sole, a major problem for this flatfish aquaculture. This study evaluated the frequency of vertebral anomalies in postlarvae and juvenile Senegalese sole fed with Artemia spp. metanauplii enriched with four commercial products (EA, EB, EC, and ED) in a fish farm. The results show a high percentage of individuals with skeletal anomalies in every dietary group. Some types of anomalies were very frequent in all diet-age groups, indicating the presence of a common trend or mainstay of vertebral deformities. Despite some variations in the frequency of anomalies among diets, it was not possible to establish a clear effect of the enrichment products on the development of vertebral deformities at both rearing stages, probably for the “masking effect” of other rearing conditions. The multivariate statistical technique, as the correspondence analysis, indicated a different anomaly pattern among ages, where bone adaptative responses may be implied.

Abstract

The high incidence of skeletal anomalies in Senegalese sole (Solea senegalensis) still constitutes a bottleneck constraining its production. There are diverse commercially available products for the enrichment of live preys, but few reports of their influence on skeletogenesis in Senegalese sole. This study evaluated the presence of vertebral anomalies in postlarvae and juvenile Senegalese sole fed with Artemia spp. metanauplii enriched with four commercial products (EA, EB, EC, and ED) in a fish farm. The most frequent alterations consisted of deformations of the neural/haemal arches and spines and fusions and deformations of hypurals, epural, or parhypural. The correspondence analysis ordered fish from each age in separated semiaxis, indicating the presence of different anomaly patterns for the two sampled stages. The results showed only very light changes in the frequency of vertebral abnormalities among tested enrichment products, i.e., individuals from EC and EA lots displayed less vertebral body anomalies and/or vertebral column deviations at 31 and 105 days after hatching, respectively. The existence of a large shared malformation pattern in all the experimental groups leads to impute to the rearing conditions as the main driving factor of the onset of such group of anomalies, probably masking some dietary effect.

Effects of different rearing temperatures on muscle development and stress response in the early larval stages of Acipenser baerii

The present study aims at investigating muscle development and stress response in early stages of Siberian sturgeon when subjected to different rearing temperatures, by analysing growth and development of the muscle and by assessing the stress response of yolk-sac larvae. Siberian sturgeon larvae were reared at 16°C, 19°C and 22°C until the yolk-sac was completely absorbed. Sampling timepoints were: hatching, schooling and complete yolk-sac absorption stage. Histometrical, histochemical and immunohistochemical analyses were performed in order to characterize muscle growth (total muscle area, TMA; slow muscle area, SMA; fast muscle area, FMA), development (anti-proliferating cell nuclear antigen -PCNA or anticaspase) as well as stress conditions by specific stress biomarkers (heat shock protein 70 or 90, HSP70 or HSP90). Larvae subjected to the highest water temperature showed a faster yolk-sac absorption. Histometry revealed that both TMA and FMA were larger in the schooling stage at 19°C while no differences were observed in the SMA at any of the tested rearing temperatures. PCNA quantification revealed a significantly higher number of proliferating cells in the yolk-sac absorption phase at 22°C than at 16°C. HSP90 immunopositivity seems to be particularly evident at 19°C. HPS70 immunopositivity was never observed in the developing lateral muscle.

Poly-β-hydroxybutyrate administration during early life: effects on performance, immunity and microbial community of European sea bass yolk-sac larvae

The reliable production of marine fish larvae is one of the major bottlenecks in aquaculture due to high mortalities mainly caused by infectious diseases. To evaluate if the compound poly-β-hydroxybutyrate (PHB) might be a suitable immunoprophylactic measure in fish larviculture, its capacity to improve immunity and performance in European sea bass (Dicentrarchus labrax) yolk-sac larvae was explored. PHB was applied from mouth opening onwards to stimulate the developing larval immune system at the earliest possible point in time. Larval survival, growth, microbiota composition, gene expression profiles and disease resistance were assessed. PHB administration improved larval survival and, furthermore, altered the larva-associated microbiota composition. The bacterial challenge test using pathogenic Vibrio anguillarum revealed that the larval disease resistance was not influenced by PHB. The expression profiles of 26 genes involved e.g. in the immune response showed that PHB affected the expression of the antimicrobial peptides ferritin (fer) and dicentracin (dic), however, the response to PHB was inconsistent and weaker than previously demonstrated for sea bass post-larvae. Hence, the present study highlights the need for more research focusing on the immunostimulation of different early developmental stages for gaining a more comprehensive picture and advancing a sustainable production of high quality fry.

Comparative ontogenetic development of two marine teleosts, gilthead seabream and European sea bass: New insights into nutrition and immunity

Gilthead seabream and European sea bass are two of the most commonly farmed fish species. Larval development is critical to ensure high survival rates and thus avoid unacceptable economic losses, while nutrition and immunity are also important factors. For this reason this paper evaluates the ontogenetic development of seabream and sea bass digestive and immune systems from eggs to 73 days post-fertilisation (dpf) by assessing the expression levels of some nutrition-relevant (tryp, amya, alp and pept1) and immune-relevant (il1b, il6, il8, tnfa, cox2, casp1, tf, nccrp1, ighm and ight) genes. The results point to similar ontogenetic development trends for both species as regard nutrition and differences in some immunity related genes.

Changes on digestive enzymes during initial ontogeny in the three-spot cichlid Cichlasoma trimaculatum

A study was performed in order to understand the development of digestive enzymes during initial ontogeny of Cichlasoma trimaculatum, for which the activity of acidic and alkaline proteases, lipases, amylases and phosphatases was determined by means of biochemical and electrophoretic analysis. Our results showed that the activity of alkaline proteases, trypsin and chymotrypsin is present from day 6 after hatching (dah) during exogenous feeding with Artemia nauplii. The activities of carboxypeptidase A and leucine aminopeptidase are present from the first days, increasing at 6 dah and reaching their maximum activity at 9 dah while acid protease activity started at 9 dah. Furthermore, the lipase activity is detected on 6 dah and keeps increasing and decreasing on 17 dah. Amylase activity is detected on 3 dah, presenting fluctuations until 45 dah, where it reaches its maximum activity. Acid and alkaline phosphatases are detected from 3 dah and reach a maximum activity between 13 and 19 dah. The SDS-PAGE electrophoresis revealed six types of bands in the alkaline proteases, with molecular weight between 113.4 and 20.4 kDa. First three bands appear on 6 dah, but it is until 11 dah when all isoforms appear. Based on these results, it is considered that this species completes its digestive enzymatic machinery from day 9 after hatching, therefore is recommended to perform the transition from live feed to inert feed at 15 dah.

Transcriptional assessment by microarray analysis and large-scale meta-analysis of the metabolic capacity of cardiac and skeletal muscle tissues to cope with reduced nutrient availability in Gilthead Sea Bream (Sparus aurata L.)

The effects of nutrient availability on the transcriptome of cardiac and skeletal muscle tissues were assessed in juvenile gilthead sea bream fed with a standard diet at two feeding levels: (1) full ration size and (2) 70 % satiation followed by a finishing phase at the maintenance ration. Microarray analysis evidenced a characteristic transcriptomic profile for each muscle tissue following changes in oxidative capacity (heart > red skeletal muscle > white skeletal muscle). The transcriptome of heart and secondly that of red skeletal muscle were highly responsive to nutritional changes, whereas that of glycolytic white skeletal muscle showed less ability to respond. The highly expressed and nutritionally regulated genes of heart were mainly related to signal transduction and transcriptional regulation. In contrast, those of white muscle were enriched in gene ontology (GO) terms related to proteolysis and protein ubiquitination. Microarray meta-analysis using the bioinformatic tool Fish and Chips ( http://fishandchips.genouest.org/index.php ) showed the close association of a representative cluster of white skeletal muscle with some of cardiac and red skeletal muscle, and many GO terms related to mitochondrial function appeared to be common links between them. A second round of cluster comparisons revealed that mitochondria-related GOs also linked differentially expressed genes of heart with those of liver from cortisol-treated gilthead sea bream. These results show that mitochondria are among the first responders to environmental and nutritional stress stimuli in gilthead sea bream, and functional phenotyping of this cellular organelle is highly promising to obtain reliable markers of growth performance and well-being in this fish species.

Ontogenetic expression of metabolic genes and microRNAs in rainbow trout alevins during the transition from the endogenous to the exogenous feeding period

As oviparous fish, rainbow trout change their nutritional strategy during ontogenesis. This change is divided into the exclusive utilization of yolk-sac reserves (endogenous feeding), the concurrent utilization of yolk reserves and exogenous feeds (mixed feeding) and the complete dependence on external feeds (exogenous feeding). The change in food source is accompanied by well-characterized morphological changes, including the development of adipose tissue as an energy storage site, and continuous muscle development to improve foraging. The aim of this study was to investigate underlying molecular mechanisms that contribute to these ontogenetic changes between the nutritional phenotypes in rainbow trout alevins. We therefore analyzed the expression of marker genes of metabolic pathways and microRNAs (miRNAs) important in the differentiation and/or maintenance of metabolic tissues. In exogenously feeding alevins, the last enzyme involved in glucose production (g6pca and g6pcb) and lipolytic gene expression (cpt1a and cpt1b) decreased, while that of gk, involved in hepatic glucose use, was induced. This pattern is consistent with a progressive switch from the utilization of stored (gluconeogenic) amino acids and lipids in endogenously feeding alevins to a utilization of exogenous feeds via the glycolytic pathway. A shift towards the utilization of external feeds is further evidenced by the increased expression of omy-miRNA-143, a homologue of the mammalian marker of adipogenesis. The expression of its predicted target gene abhd5, a factor in triglyceride hydrolysis, decreased concurrently, suggesting a potential mechanism in the onset of lipid deposition. Muscle-specific omy-miRNA-1/133 and myod1 expression decreased in exogenously feeding alevins, a molecular signature consistent with muscle hypertrophy, which may be linked to nutritional cues or increased foraging.

The ontogeny of New Zealand groper (Polyprion oxygeneios) lymphoid organs and IgM

This study investigates the ontogeny of New Zealand groper (Polyprion oxygeneios) immune system, a new species for aquaculture in the Southern Pacific Ocean. In the eggs, both lysozyme and IgM were detected. Egg IgM was found at 1.07-1.56 μg/g wet weight and consisted of monomers compared to the polymerized IgM found in adult serum. In larvae, the head-kidney (HK) was first observed at 6 dph, followed by the spleen at 16 dph, and thymus at 20 dph, and within these organs IgM(+) cells were first detected in the HK (12 dph), then the spleen (32 dph) and finally in the thymus and the gastrointestinal tract (45 dph). Low levels of Igμ heavy chain transcripts were detected at 2 and 3 dph and they increased at 9 dph. Igμ expression further increased from day 45 onwards. In juveniles (115 dph), the HK and blood showed similar percentages of IgM(+) cells as the adult groper. These results highlight the important maturation steps that occur during the development of the immune system in the marine teleost P. oxygeneios.

Digestive enzymatic activity on tropical gar (Atractosteus tropicus) larvae fed different diets

Digestive enzymatic activity and growth performance on tropical gar (Atractosteus tropicus) larvae fed Artemia nauplii (LF), frozen adult Artemia (AB), an artificial diet (AF) with 46% protein and 16% lipids and a starvation group (SG) from first feeding (5 days after hatching-5 DAH) to 34 DAH were studied. All larvae under starvation (SG) died at 15 DAH. By the end of the experimental period, morphological variables (total length, wet weight and specific growth rate) were significant in larvae fed AF compared to LF and AB. All enzymes studied in the experiment were present since the start of exogenous feeding (including pepsin) and the enzymatic activity varied with the diets. Low levels of enzymatic activity were observed until the 29 DAH; however, after this moment, there was a significant increase (eightfold), particularly for the AF treatment. In vitro protein digestibility tests performed with enzymatic extracts showed that artificial diets with 52% protein and 14% lipids were better digested by larvae before 30 DAH, while diets with 45% protein and 11% lipids were better digested after this age. Taking into account the better growth performance, higher enzymatic activity and better protein digestibility obtained, artificial diets can be used since the start of exogenous feeding on tropical gar larvae, as in other lepisosteids.