Nutritional requirements of fish

An In-Depth Insight into the Profile, Mechanisms, Functions, and Transfer of Essential Amino Acids from Mulberry Leaves to Silkworm Bombyx mori L. Pupae and Fish

The silkworm Bombyx mori, the second most varied group of insects, is a fascinating insect that belongs to the Lepidoptera species. We aimed to deepen our knowledge about the composition and significance of amino acids (AA) from the sericulture chain to fish. AAs are the most prevalent molecules throughout the growth process of silkworms. We described AAs classification, occurrence, metabolism, and functions. Online datasets revealed that the essential AAs (EAA) level in fish meal and silkworm pupae (SWP) is comparable. SWP have a high content of methionine and lysine, which are the principal limiting AAs in fish diets, indicating that SWP have nutritional potential to be added to fish diets. Additionally, an overview of the data analyzed displays that SWP have a higher protein efficiency ratio than fish meal, the classical protein-rich source (>1.19 times), and compared to soybean meal, the second-most preferred source of protein in aquaculture (>2.08 times), indicating that SWP can be considered effective for animal feeding. In this study, we provide an overview of the current knowledge concerning AAs, paying special emphasis to EAAs and explaining, to some extent, certain mechanisms and functions of these compounds, from mulberry leaves to larvae-pupae and fish diets.

Effects of Carbohydrase Supplementation on Growth Performance, Intestinal Digestive Enzymes and Flora, Glucose Metabolism Enzymes, and glut2 Gene Expression of Hybrid Grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) Fed Different CHO/L Ratio Diets

An optimal carbohydrate-to-lipid (CHO: L) ratio facilitates fish growth and protein conservation, and carbohydrase promotes nutrient absorption. Therefore, an 8-week feeding trial was conducted to investigate the effects of carbohydrase supplementation on growth performance, intestinal digestive enzymes and flora, glucose metabolism enzymes and glut2 gene expression in juvenile hybrid grouper (Epinephelus fuscoguttatus♀× Epinephelus lanceolatus♂) fed different CHO: L ratios diets. L, M, and H represent CHO:L ratios of 0.91, 1.92 and 3.91, respectively. LE, ME, and HE represent CHO:L ratios of 0.91, 1.92, 3.91, respectively, supplemented with the same ratio of carbohydrase. Results showed that weight gain rate (WGR) and specific growth rate (SGR) reached a maximum in group M and were significantly enhanced by carbohydrase (p < 0.05). Crude lipid content decreased significantly with an increase in the dietary CHO:L ratio (p < 0.05). Significant increases in the trypsin (TRY) and amylase (AMS) activities and significant decreases in the lipase (LPS) activity were observed with increasing dietary CHO:L ratio, and the former two were significantly promoted by carbohydrase (p < 0.05). The content of liver and muscle glycogen increased significantly with the increasing dietary CHO:L ratio but decreased significantly after carbohydrase supplementation (p < 0.05). The glucokinase (GK), pyruvate kinase (PK), Phosphate 6 fructokinase-1 (PFK-1) and phosphoenolpyruvate kinase (PEPCK) activities increased significantly with increasing dietary CHO:L ratio (p < 0.05). Glut2 mRNA expression decreased significantly in liver and increased significantly in intestine with increasing dietary CHO:L ratio (p < 0.05). By linear discriminant analysis (LDA), the abundance of Alistipe was significantly higher in Group ME than in Group M. These results suggested that hybrid grouper can only moderately utilize dietary carbohydrate and lipid in diet, and a certain amount of high glycemic lipids occurred when fed with high-carbohydrate diets. By the weight gain for basis, the supplementation of carbohydrase in Group H with amylase, glycosylase, and pullulanase in a 1:1:1 ratio effectively lowered glycemic lipids, promoted the growth of grouper, digestive enzymes activities and carbohydrate metabolic enzyme, and glut2 gene expression in intestine, effectively balancing the negative effects of high-carbohydrate diet and improving the utilization of carbohydrate.

Genetic Analysis of the Fatty Acid Profile in Gilthead Seabream (Sparus aurata L.)

Simple Summary

Humans require essential fatty acids in their diet and marine fish are a source of them, especially omega3 fatty acids that present high benefits on diverse vascular diseases and the immune system. Breeding programs in gilthead seabream usually include growth as the first criterion in the selection process of the fish. However, that could lead to fish with a higher fillet fat content and a fatty acid profile with a lower polyunsaturated fatty acids percentage. Fillet fat content and its fatty acids profile have been revealed as heritable traits. Therefore, further studies to go deeper in the selection process are advisable.

Abstract

The gilthead seabream is one of the most valuable species in the Mediterranean basin both for fisheries and aquaculture. Marine fish, such as gilthead seabream, are a source of n3 polyunsaturated fatty acids, highly appreciated for human food owing to their benefits on the cardiovascular and immune systems. The aim of the present study was to estimate heritability for fatty acid (FA) profile in fillet gilthead seabream to be considered as a strategy of a selective breeding program. Total of 399 fish, from a broodstock Mediterranean Sea, were analysed for growth, flesh composition and FA profile. Heritabilities for growth traits, and flesh composition (fat, protein, and moisture content) were medium. Heritability was moderate for 14:0, 16:0 and 18:1n9 and for sum of monounsaturated FA and n6/n3 ratio, and it was low for 20:1n11 and 22:6n3 and the ratio unsaturated/saturated FA. Breeding programs in gilthead seabream usually include growth as the first criterion in the selection process of the fish. However, other quality traits, such as fillet fat content and its fatty acids profile should be considered, since they are very important traits for the consumer, from a nutritional point of view and the benefits for the health.

Dietary docosahexaenoic acid decreased lipid accumulation via inducing adipocytes apoptosis of grass carp, Ctenopharygodon idella

The purpose of this study was to explore the mechanism of by which docosahexaenoic acid (DHA) inhibit the accumulation of adipose tissue lipid in grass carp (Ctenopharyngodon idella). We therefore designed two semi-purified diets, namely DHA-free (control) and DHA-supplemented, and fed them to grass carp (22.19 ± 1.76 g) for 3 and 6 weeks. DHA supplementation led to a significantly lower intraperitoneal fat index (IPFI) than that in the control group by reducing the number of adipocytes but significantly higher adipocyte size (P < 0.05). In the intraperitoneal adipose tissue, the DHA-fed group showed significantly higher peroxisome proliferator-activated receptor (PPAR)γ, CCAAT enhancer-binding protein (C/EBP)α, and sterol regulatory element-binding protein (SREBP)1c mRNA expression levels at both 3 and 6 weeks (P < 0.05). However, the ratio of the expression levels of B cell leukemia 2 (Bcl-2) and Bcl-2-associated X protein (Bax) was significantly lower in the DHA-fed group than in the control group (P < 0.05), and the protein expression levels of the apoptosis-related proteins caspase 3, caspase 8, and caspase 9 were also significantly higher (P < 0.05). Overall, although DHA promotes lipid synthesis, it is more likely that DHA could suppress the lipid accumulation in adipocytes of grass carp by inducing adipocyte apoptosis.

Relative influence of dietary protein and energy contents on lysine requirements and voluntary feed intake of rainbow trout fry

The effect of dietary digestible protein (DP) and/or digestible energy (DE) levels on lysine (Lys) requirements, Lys utilisation efficiency and voluntary feed intake (VFI) were studied in rainbow trout fry when Lys was the first limiting indispensable amino acid or in excess in the diet. Two trials were conducted at 11·6°C with eighty-one experimental diets, containing 280 g DP/kg DM (low protein (LP), trial 1), 600 g DP/kg DM (high protein (HP), trial 1) or 440 g DP/kg DM (medium protein (MP), trial 2), 17 MJ DE/kg (low energy (LE)), 19·5 MJ DE/kg (medium energy (ME)) or 22 MJ DE/kg (high energy (HE)), and nine Lys levels from deeply deficient to large excess (2·3-36 g/kg DM). Each diet was given to apparent satiety to one group of fifty fry (initial body weight 0·85 g) for 24 (MP diets, trial 2) or 30 (LP and HP diets, trial 1) feeding days. Based on N gain data fitted with the broken-line model, the relative Lys requirement was significantly different with the dietary DP level, from 13·3-15·7 to 22·9-26·5 g/kg DM for LP and HP diets, respectively, but did not significantly change with the DE level for a same protein level. The Lys utilisation efficiency for protein growth above maintenance was constant across diets, suggesting no effect of either dietary DE or DP levels. In Lys excess, the VFI was markedly decreased by the DP level but not by the extra DE supply. Our results suggest that the relative Lys need is best expressed in terms of percentage of protein content for optimum fish feed formulation, at least in rainbow trout fry.

Regulation of adipocytes lipolysis by n-3 HUFA in grass carp (Ctenopharyngodon idellus) in vitro and in vivo

N-3 highly unsaturated fatty acids (n-3 HUFA) have been shown to inhibit body fat accumulation in animals. To clarify the mechanism of this fat-lowering effect of n-3 HUFA in grass carp (Ctenopharyngodon idellus), two experiments were conducted. In experiment 1, isolated grass carp mature adipocytes were incubated with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) at different concentrations for 6 h. The release of glycerol to the medium was detected, and the expression of the lipolysis-related genes was analyzed. In experiment 2, a 95-day feeding trial was conducted with two diets formulated with either lard oil (as control) or fish oil (supplying n-3 HUFA as treatment) as the main lipid source. The glycerol and free fatty acid (FFA) released from the isolated adipocytes of both groups were detected after the feeding period. The expression of select lipolysis-related genes in adipose tissue was also analyzed. The results from experiment 1 showed that the release of glycerol was significantly increased by DHA and EPA (P < 0.05). Moreover, the expression of lipolysis-related genes, such as adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), tumor necrosis factor α (TNFα) and leptin, was also significantly elevated in the treatment group (P < 0.05). Experiment 2 demonstrated that glycerol and FFA release from the isolated adipocytes were significantly higher in the treatment group compared to the control group (P < 0.05). The expression level of ATGL, HSL, TNFα and leptin in the treatment group was significantly higher than in the control group (P < 0.05). The present results provide novel evidence that n-3 HUFAs could regulate grass carp adipocyte lipolysis in vitro or in vivo, and the effect might be in part associated with their influence on the expression of lipolysis-related genes and lipolysis-related adipokines genes.

Effects of the total replacement of fish-based diet with plant-based diet on the hepatic transcriptome of two European sea bass (Dicentrarchus labrax) half-sibfamilies showing different growth rates with the plant-based diet

Background

Efforts towards utilisation of diets without fish meal (FM) or fish oil (FO) in finfish aquaculture have been being made for more than two decades. Metabolic responses to substitution of fishery products have been shown to impact growth performance and immune system of fish as well as their subsequent nutritional value, particularly in marine fish species, which exhibit low capacity for biosynthesis of long-chain poly-unsaturated fatty acids (LC-PUFA). The main objective of the present study was to analyse the effects of a plant-based diet on the hepatic transcriptome of European sea bass (Dicentrarchus labrax).

Results

We report the first results obtained using a transcriptomic approach on the liver of two half-sibfamilies of the European sea bass that exhibit similar growth rates when fed a fish-based diet (FD), but significantly different growth rates when fed an all-plant diet (VD). Overall gene expression was analysed using oligo DNA microarrays (GPL9663). Statistical analysis identified 582 unique annotated genes differentially expressed between groups of fish fed the two diets, 199 genes regulated by genetic factors, and 72 genes that exhibited diet-family interactions. The expression of several genes involved in the LC-PUFA and cholesterol biosynthetic pathways was found to be up-regulated in fish fed VD, suggesting a stimulation of the lipogenic pathways. No significant diet-family interaction for the regulation of LC-PUFA biosynthesis pathways could be detected by microarray analysis. This result was in agreement with LC-PUFA profiles, which were found to be similar in the flesh of the two half-sibfamilies. In addition, the combination of our transcriptomic data with an analysis of plasmatic immune parameters revealed a stimulation of complement activity associated with an immunodeficiency in the fish fed VD, and different inflammatory status between the two half-sibfamilies. Biological processes related to protein catabolism, amino acid transaminations, RNA splicing and blood coagulation were also found to be regulated by diet, while the expression of genes involved in protein and ATP synthesis differed between the half-sibfamilies.

Conclusions

Overall, the combined gene expression, compositional and biochemical studies demonstrated a large panel of metabolic and physiological effects induced by total substitution of both FM and FO in the diets of European sea bass and revealed physiological characteristics associated with the two half-sibfamilies.

Heritability and mechanisms of n-3 long chain polyunsaturated fatty acid deposition in the flesh of Atlantic salmon

n-3 long chain polyunsaturated fatty acids (n-3LC-PUFA) are essential components of vertebrate membrane lipids and are now at critically low levels in modern Western diets. The main human dietary source for n-3LC-PUFA is fish and seafood, and over 50% of global fish production is currently supplied by aquaculture. However, increasing pressure to include vegetable oils, which are devoid of n-3LC-PUFA, in aquaculture feeds reduces their content in farmed fish flesh. The aim of this study was to measure the heritability and infer mechanisms determining flesh n-3LC-PUFA content in Atlantic salmon. This was achieved by analysing flesh lipid parameters in 48 families of Atlantic salmon and by measuring differences, by high density microarray, in hepatic mRNA expression in families with high and low flesh n-3LC-PUFA. The results show that flesh n-3LC-PUFA composition is a highly heritable trait (h²=0.77±0.14). Gene ontology analysis of differentially expressed genes indicates increased hepatic lipid transport, likely as very low density lipoprotein (VLDL), and implicates family differences in transforming growth factor β1 (Tgfβ1) signalling, activities of a transcription factor Snai1, and considered together may indicate alterations in hepatic nuclear factor 4α (HNF4α), a master controller of lipid homeostasis. This study paves the way for identification of quantitative trait loci and gene interaction networks that are associated with flesh n-3LC-PUFA composition, which will assist the sustainable production of Atlantic salmon and provide optimal levels of critical nutrients for human consumers.

Malathion-induced alteration of the antioxidant defence system in kidney, gill, and intestine of Carassius auratus gibelio

Pesticides such as malathion, commonly used in agriculture and households, are toxic substances that lead to reactive oxygen species generation, which harms organisms. Ecotoxicological consequences of malathion, particularly its effects on antioxidants in fish, are not well understood. Thus, we investigated the effects of malathion (0.05 mg/L) on lipid peroxidation and antioxidant systems in Carassius auratus gibelio kidney, intestine, and gills following exposure times of 1, 2, 3, and 6 days. The lipid peroxidation and antioxidative defense mechanisms display different responses in investigated tissues. The lipid peroxidation was increased in all investigated tissues, especially after 1 day of malathion administration. Changes in reduced glutathione levels have been registered, mainly after 6 days of pesticide exposure. The modulation in the activities of antioxidant enzymes, catalase, gluthatione peroxidase, glutathione reductase, and glutathione-S-transferase was time and tissue specific. The investigated parameters can be used as biomarkers of fish exposure to malathion.

Determination of oxytetracycline levels in rainbow trout serum on a biphenyl column using high-performance liquid chromatography

We developed a simple and sensitive high-performance liquid chromatography method on a biphenyl column to determine oxytetracycline (OTC) levels in rainbow trout serum. The assay used deproteination, filtration, and subsequent separation on a reverse-phase biphenyl column, with UV detection at 355 nm. OTC (7.8-7.9 min) was completely resolved from structurally similar riboflavin (10.4-10.5 min), a common feed supplement. Estimated limits of detection and quantitation of OTC were 0.01 and 0.04 microg/mL, respectively. The average recovery for OTC was 102% with a R.S.D. of 8.34%. Calibration standards were linear from 0.01 to 10 microg/mL.

Expression of recombinant vitellogenin in the yeast Pichia pastoris

Vitellogenin (Vtg) plays vital roles as precursor to the yolk proteins and as carrier for lipids, carbohydrates, phosphates, metal ions, vitamins, and hormones into the oocytes during the massive deposition of yolk nutrients for subsequent nourishment of the developing embryos. Reproductive success is highly sensitive to the nutritional quality of the broodstock diet, which greatly affects the egg and larval viability. We present a novel strategy for genetically engineering a Pichia pastoris yeast strain that constitutively produces recombinant Vtg (rVtg), for application as an enriched feed. The tilapia Oreochromis aureus Vtg (OaVtg) cDNA (5.3 kb) was cloned into a nonsecretory pGAPZA vector. Clones containing up to 31 copies of glyceraldehyde-3-phosphate dehydrogenase (GAP)-promoter-driven Vtg expression cassettes were isolated. These clones expressed a membrane-associated intracellular rVtg protein of 194 kDa, constituting up to 1.16% of total protein. To facilitate future purification of rVtg, we explored the possibility of secreting rVtg using the native Vtg secretion signal and the alpha-factor secretion signal of Saccharomyces cerevisiae. However, neither signal promoted the secretion of rVtg. The clones maximally expressed rVtg at 23 degrees C, reaching a peak at 22 h in shake flasks and 16 h in a fermentor. The clones exhibited a significant increase in essential amino acids and long-chain polyunsaturated fatty acids, which are important for its application as a high-quality nutrient feed.