Effects of resveratrol and genistein on growth,nutrient utilization and fatty acid composition of rainbow trout

The replacement of the finite and costly resource fish oil is an important task for aquaculture nutrition. A promising approach could be the use of plant bioactives that may have the potential to influence the metabolism and the synthesis of n-3 long chain polyunsaturated fatty acids, especially EPA (20:5n-3) and DHA (22:6n-3). In this study, the two phytochemicals resveratrol (RV) and genistein (G) were investigated for their effects on fish growth, nutrient utilization and body nutrient composition alongside their effects on whole body fatty acid (FA) composition. In a feeding trial lasting 8 weeks, rainbow trout (initial BW: 81.4±0.5 g) were held in a recirculating aquaculture system and fed six experimental diets with varying fish oil levels as plain variants or supplemented with 0.3% of dry matter (DM) of either RV or G. The six diets were as follows: diet F4 had 4% DM fish oil, diet F0 had 0% DM fish oil, diets F4+RV, F4+G, F0+RV and F0+G were equal to the diets F4 and F0, respectively, and supplemented with the phytochemicals RV and G. The feeding of the F0+RV diet resulted in reduced feed intake, growth rate and slightly reduced whole body lipid levels. At the same time, the amount of polyunsaturated FA and the n-3/n-6 ratio were significantly increased in whole body homogenates of rainbow trout fed diet F0+RV in comparison to the F0 control. The feeding of the F0+G diet led to reduced feed intake, slightly increased protein utilization but did not significantly affect the whole body FA composition. Overall, feeding the fish oil-free diet supplemented with the phytochemicals resulted in more pronounced effects on fish performance and FA composition than the single factors per se (dietary fish oil level or phytochemical). Present data indicate that G might not be of profitable use for trout nutrition. In terms of FA composition, RV could be a potentially useful complement for fish oil. However, the impairment of growth and performance parameters as observed in the present study discourages its use in trout diets.     

Changes in microbiota of rainbow trout caused by sediments contamination

The abundance, composition and hydrocarbon-degrading bacteria, as possible biomarkers of contamination with oil hydrocarbons, of autochthonous and alochtonous microbiota of the digestive tract of rainbow trout have been estimated. The samples of the bottom sediments for microbiological tests have been collected and a response of natural bacterial communities in the digestive tract of rainbow trout and nutritional changes has been investigated. Experimental fish have been fed with a mixture of three substances with the aim to assess the influence of hydrocarbon-degrading bacteria contained in the sediments on the microbiota of rainbow trout’s digestive tracts. The abundance values of rainbow trout intestinal heterotrophic bacteria were found to change depending on alochtonous microbiota of different bottom sediments given to the experimental fish with food in vitro. According to the results of our research, it is likely that the changes in the abundance values of the microbiota of the digestive tract of fish and in the proportions of functional groups of the bacteria allow us to determine changes in the functional activity of bacteria depending on food composition. Any relative increase or decrease of abundance or activity of alochtonous microbiota allows the prediction of toxic effects of the contaminants on animals and the environment.     

Skeletal Anomaly Monitoring in Rainbow Trout (Oncorhynchus mykiss,Walbaum 1792) Reared under Different Conditions

The incidence of skeletal anomalies could be used as an indicator of the “quality” of rearing conditions as these anomalies are thought to result from the inability of homeostatic mechanisms to compensate for environmentally-induced stress and/or altered genetic factors. Identification of rearing conditions that lower the rate of anomalies can be an important step toward profitable aquaculture as malformed market-size fish have to be discarded, thus reducing fish farmers’ profits. In this study, the occurrence of skeletal anomalies in adult rainbow trout grown under intensive and organic conditions was monitored. As organic aquaculture animal production is in its early stages, organic broodstock is not available in sufficient quantities. Non-organic juveniles could, therefore, be used for on-growing purposes in organic aquaculture production cycle. Thus, the adult fish analysed in this study experienced intensive conditions during juvenile rearing. Significant differences in the pattern of anomalies were detected between organically and intensively-ongrown specimens, although the occurrence of severe, commercially important anomalies, affecting 2–12.5% of individuals, was comparable in the two systems. Thus, organic aquaculture needs to be improved in order to significantly reduce the incidence of severe anomalies in rainbow trout.     

Impact of Fishmeal Replacement in Diets for Gilthead Sea Bream (Sparus aurata) on the Gastrointestinal Microbiota Determined by Pyrosequencing the 16S rRNA Gene

Recent studies have demonstrated the impact of diet on microbiota composition, but the essential need for the optimization of production rates and costs forces farms and aquaculture production to carry out continuous dietary tests. In order to understand the effect of total fishmeal replacement by vegetable-based feed in the sea bream (Sparus aurata), the microbial composition of the stomach, foregut, midgut and hindgut was analysed using high-throughput 16S rDNA sequencing, also considering parameters of growth, survival and nutrient utilisation indices.A total of 91,539 16S rRNA filtered-sequences were analysed, with an average number of 3661.56 taxonomically assigned, high-quality sequences per sample. The dominant phyla throughout the whole gastrointestinal tract were Actinobacteria, Protebacteria and Firmicutes. A lower diversity in the stomach in comparison to the other intestinal sections was observed. The microbial composition of the Recirculating Aquaculture System was totally different to that of the sea bream gastrointestinal tract. Total fishmeal replacement had an important impact on microbial profiles but not on diversity. Streptococcus (p-value: 0.043) and Photobacterium (p-value: 0.025) were highly represented in fish fed with fishmeal and vegetable-meal diets, respectively. In the stomach samples with the vegetable diet, reads of chloroplasts and mitochondria from vegetable dietary ingredients were rather abundant. Principal Coordinate Analysis showed a clear differentiation between diets in the microbiota present in the gut, supporting the presence of specific bacterial consortia associated with the diet.Although differences in growth and nutritive parameters were not observed, a negative effect of the vegetable diet on the survival rate was determined. Further studies are required to shed more light on the relationship between the immune system and sea bream gastrointestinal tract microbiota and should consider the modulation of the microbiota to improve the survival rate and nutritive efficacy when using plant-based diets.     

Influence of dietary composition on gluconeogenesis from L-(U-14C)glutamate in rainbow trout (Salmo gairdneri)

The effect of dietary composition (high-protein, high-carbohydrate and high-fat diets) and starvation on in totum gluconeogenesis from L-(U-14C)glutamate was studied in the rainbow trout. High-fat and high-carbohydrate diets produced a significant hyperglycaemia. Lower blood glucose values were obtained in trout fed on a high-protein diet. Liver glycogen levels were significantly lower in trout fed on carbohydrate-free diets (high-protein and high-fat diets) and in starved fish. Gluconeogenesis from L-(U-14C)glutamate was markedly reduced in fish given the high-carbohydrate diet and significantly enhanced in starved fish. Radioactive liver glycogen was higher in starved fish, although the amount of radioactivity incorporated into glycogen was very low.     

Impact of black soldier fly larvae meal on the chemical and nutritional characteristics of rainbow trout fillets

The present research studied the effect of a dietary inclusion with Hermetia illucens larvae meal (Hi) on rainbow trout’s fillets chemical composition. The effect of Hi inclusion in diets on rainbow trout chemical characteristics was evaluated. Trout were fed three different diets: control (C, no Hi inclusion), 25% and 50% of substitution of fish meal with Hi (Hi25 and Hi50, respectively). Fillets were analysed to quantify proximate composition, carbohydrates percentage, colour parameters, nucleotides concentration, fatty acids profile, volatile organic compounds (VOCs) and myofibrillar and sarcoplasmic concentrations. Diets did not affect proximate composition. Contrariwise, Hi50 diet decreased fillet yellowness and both substitution percentages affected negatively adenosine monophosphate concentration. Saturated fatty acids, mostly C12 : 0, increased their contents in relation with Hi inclusion at the expense of monounsaturated and polyunsaturated (both n-3 and n-6) fatty acids. Less modifications were reported in VOCs as only heptanal and octanal concentrations were affected, no new compounds appeared in relation with Hi inclusion. No modifications in proteins patterns were shown even if myofibrillar content decreased in trout fed Hi50. The results highlighted that chemical modifications occurred in fillets were related to the chemical composition of the H. illucens meal and to the percentage of inclusion in the diet. Substitution of fish meal with a precisely percentage of H. illucens meal could be a potential future solution in order to decrease the quantity of fish meal used in aquafeeds.     

Fermented Soybean Meal Increases Lactic Acid Bacteria in Gut Microbiota of Atlantic Salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>)

The main goal of the present study was to address the effect of feeding fermented soybean meal-based diet to Atlantic salmon on gut microbiota. Further, expression of genes of interest, including cathelicidin antimicrobial peptide (cath), mucin 2 (muc2), aquaporin (aqp8ab), and proliferating cell nuclear antigen (pcna), in proximal intestine of fish fed either experimental diet was analyzed. Three experimental diets, including a control fishmeal (30% FM), soybean meal (30% SBM), or fermented soybean meal diet (30% FSBM) were randomly assigned to triplicate tanks during a 50-day trial. The PCR-TTGE showed microbiota composition was influenced by experimental diets. Bands corresponding to genus Lactobacillus and Pediococcus were characteristic in fish fed the FSBM-based diet. On the other hand, bands corresponding to Isoptericola, Cellulomonas, and Clostridium sensu stricto were only observed in fish FM-based diet, while Acinetobacter and Altererythrobacter were detected in fish fed SBM-based diet. The expression of muc2 and aqp8ab were significantly greater in fish fed the FSBM-based diet compared with the control group. Our results suggest feeding FSBM to Atlantic salmon may (1) boost health and growth physiology in fish by promoting intestinal lactic acid bacteria growth, having a prebiotic-like effect, (2) promote proximal intestine health by increasing mucin production, and (3) boost intestinal trans-cellular uptake of water. Further research to better understands the effects of bioactive compounds derived from the fermentation process of plant feedstuff on gut microbiota and the effects on health and growth in fish is required.     

Intestinal Microbiota Diversity of the Flat Fish Solea senegalensis (Kaup, 1858) Following Probiotic Administration

Pleuronectiforms are an important group of fish, and one of their species, Solea senegalensis (Kaup 1858), has been extensively studied at different levels, although information about its intestinal microbiota and the effects of different factors on it is very scarce. Modern aquaculture industry demands strategies which help to maintain a microbiologically healthy environment and an environmentally friendly aquaculture. In this context, probiotics seem to offer an attractive alternative. The intake of probiotics could modify the composition of the intestinal microbiota, which is a key component in excluding potential invaders and maintaining health. The aim of this study was to evaluate by 16S rRNA gene analysis using polymerase chain reaction-denaturing gradient gel electrophoresis the effect of administering fresh or lyophilized cells of Pdp11 on the intestinal microbiota of farmed Senegalese sole, using sodium alginate to facilitate the incorporation of bacterial cells to the feed. The results obtained showed that the composition of fish intestinal microbiota was affected when fish received a diet supplemented with sodium alginate and fresh or lyophilized probiotic cells. In all cases, the dominant bacterial groups belonged to γ-Proteobacteria and mainly the Vibrio species. The use of sodium alginate reduced the incidence of populations with <97% 16S rRNA gene sequence identity to uncultured microorganisms in the intestinal microbiota until non-detected limits. On the other hand, the supplementation of the diet with probiotics produced an increase of the predominant species related to Vibrio genus.     

The influence of season and levels of dietary lipid on growth performance and lipid composition in rainbow trout <Emphasis Type="Italic">Parasalmo mykiss</Emphasis> (Walbaum, 1792)

We studied the growth performance and lipid composition of liver, muscles and visceral fat in rainbow trout Parasalmo mykiss (Walbaum, 1792) and the diets used in its cultivation during the spring-summer season. The differences in dietary lipid composition determined modifications in the biochemical composition of tissues of rainbow trout and had an effect on the weight and growth rate of the fish. Trophic and seasonal factors also had their influence on the studied parameters. The degree of influence depended on the functional characteristics of tissues and organs of rainbow trout.     

The red alga Porphyra dioica as a fish-feed ingredient for rainbow trout (Oncorhynchus mykiss): effects on growth, feed efficiency, and carcass composition

Porphyra dioica meal was added at levels of 5, 10 and 15% to a diet for rainbow trout formulated to be isonitrogenous and isolipidic. The control diet was a commercial trout diet without seaweed meal. The experimental groups were fed in triplicate for 12.5 weeks, during which fish weight increased on average from 107–261 g. Seaweed meal inclusion did not affect significantly weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and apparent digestibility coefficient of the dry matter (ADC_dm) for any of the diets. Voluntary feed intake (VFI) increased for all seaweed diets compared to the control diet but not significantly (P?>?0.05). Final weight (FW) was significantly smaller for the 15% P. dioica inclusion and hepatosomatic index (HSI) for the 10% and 15% inclusion. Carcass protein content increased for all three experimental diets, and was significantly higher for the diet with 10% seaweed inclusion. Rainbow trout fed with Porphyra meal presented a dark orange pigmentation of the flesh at the end of the trial, compared to the whitish color from the control fish. These results suggest that P. dioica can effectively be included in diets for rainbow trout up to 10% without significant negative effects on weight gain and growth performance. The pigmentation effect of the fish flesh by adding P. dioica meal to the feed is of a considerable interest to the organic salmon-farming industry.     

Effect of diets containing sesame oil on growth and fatty acid composition of rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate effects of fish oil replacement by sesame oil in combination with other vegetable oils in diets with regard to growth performance, feed utilization, desaturation and elongation, whole fish and liver fatty acid profiles of juvenile rainbow trout. Sesame oil (SO) used in the feeds was a mixture of linseed (LO), sunflower (SFO) and fish oil (FO), whereas the control diet contained only FO. Duplicate groups of 60 rainbow trout (~7 g) held under similar culture conditions were fed 2% of their body weight per day for 75 days. At the end of feeding trials, there was no difference in feed utilization efficiency or growth performance between the control group and the groups with added sesame oil (P > 0.05). However, viscerosomatic and hepatosomatic index values were significantly higher (P < 0.05) in fish fed with FO30/SO35/SFO35 diets. Results showed that total body lipid levels of fish fed diets containing sunflower oil were higher than in the other experimental groups (P < 0.05). However, crude lipid levels were similar in fish fed the control diet and the diet with sesame oil (FO30/LO35/SO35), which is sunflower oil‐free. Crude lipid levels of fish livers were not influenced by the diets (P > 0.05). Diets with sesame oil increased desaturation and elongation of 18 : 3n‐3 towards n‐3 HUFA. The conclusion was that the diet addition of sesame oil in combination with other vegetable oils increased the nutritional quality of the whole fish and liver of juvenile rainbow trout, in particular the docosahexaenoic acid (DHA) level. Therefore, sesame oil may be of interest for use in aquaculture.     

Selection for Adaptation to Dietary Shifts: Towards Sustainable Breeding of Carnivorous Fish

Genetic adaptation to dietary environments is a key process in the evolution of natural populations and is of great interest in animal breeding. In fish farming, the use of fish meal and fish oil has been widely challenged, leading to the rapidly increasing use of plant-based products in feed. However, high substitution rates impair fish health and growth in carnivorous species. We demonstrated that survival rate, mean body weight and biomass can be improved in rainbow trout (Oncorhynchus mykiss) after a single generation of selection for the ability to adapt to a totally plant-based diet (15.1%, 35.3% and 54.4%, respectively). Individual variability in the ability to adapt to major diet changes can be effectively used to promote fish welfare and a more sustainable aquaculture.     

Breeding salmonids for feed efficiency in current fishmeal and future plant-based diet environments

The aquaculture industry is increasingly replacing fishmeal in feeds for carnivorous fish with soybean meal (SBM). This diet change presents a potential for genotype-environment (G × E) interactions. We tested whether current salmonid breeding programmes that evaluate and select within fishmeal diets also improve growth and efficiency on potential future SBM diets. A total of 1680 European whitefish from 70 families were reared with either fishmeal- or SBM-based diets in a split-family design. Individual daily gain (DG), daily feed intake (DFI) and feed efficiency (FE) were recorded. Traits displayed only weak G × E interactions as variances and heritabilities did not differ substantially between the diets, and cross-diet genetic correlations were near unity. In both diets, DFI exhibited moderate heritability and had very high genetic correlation with DG whereas FE had low heritability. Predicted genetic responses demonstrated that selection to increase DG and FE on the fishmeal diet lead to favourable responses on the SBM diet. Selection for FE based on an index including DG and DFI achieved at least double FE gain versus selection on DG alone. Therefore, current breeding programmes are improving the biological ability of salmonids to use novel plant-based diets, and aiding the aquaculture industry to reduce fishmeal use.     

The effect of peptide absorption on PepT1 gene expression and digestive system hormones in rainbow trout (Oncorhynchus mykiss)

The present study evaluates the effect of protein source (dipeptides, free amino acids, and intact protein) on development and growth of Salmonid fish alevin. Specifically, we follow the expression of oligopeptide transporter protein PepT1 in the intestine of rainbow trout (Oncorhynchus mykiss). Fish were fed exogenously one of four diets: three formulated (lysyl–glycine dipeptide supplemented diet — PP, free lysine and glycine supplemented diet — AA, control diet with no lysine — CON) or commercial starter (Aller Futura — AF). Fish increased mean body weight 8 fold with PP- and AA-supplemented diets resulting in significantly higher weight gain than fish fed CON. Statistical analysis revealed a significant increase in relative PepT1 expression of fish fed experimental diets. Immunohistochemical staining with PepT1 antibody showed the presence of the transporter protein in the brush border membrane of the proximal intestinal enterocytes of fish from all experimental groups. Leptin immunoreactivity occurred not only in the gastric glands but also in proximal intestine and pyloric caeca of fish fed PP, AA and AF diets. Leptin immunoreactivity was also observed in hepatocyte cytoplasm and pancreatic acinar cells. Gastrin/CCK immunoreactive cells were present in the proximal intestine and pyloric caeca.     

Evaluation of Lactobacillus paracasei subsp. tolerans isolated from Jenyn's sprat (Ramnogaster arcuata) as probiotic for juvenile rainbow trout Oncorhynchus mykiss (Walbaum, 1792)

A lactic acid bacterial strain, Lactobacillus paracasei subsp. tolerans F2, isolated from the intestine of Ramnogaster arcuata, was evaluated as a growth promoter in juvenile rainbow trout Oncorhynchus mykiss (Walbaum, 1972) farming. In addition, the safety of the strain was assessed according to the FAO recommendations. Strain F2 was susceptible to most antibiotics tested and no evidence of hemolytic activity was found. When the strain of Lactobacillus paracasei subsp. tolerans F2 was administered with food, no adverse effects on health were observed and fish biomass increased 12% more in the treatment group than in the control group. Significant differences were detected in the specific growth rate and feed conversion ratio. In the group receiving Lactobacillus paracasei subsp. tolerans F2‐supplemented feed, quantitative differences in the microbial composition of fish feces with respect to the control group were observed. An important decrease in fungi and enterobacteria was observed in feces from the treatment group, coincident with an increase in lactic acid bacteria. This result would indicate a change in the composition of the intestinal microbiota of fish treated with the putative probiotic. These results suggest that the strain of Lactobacillus paracasei subsp. tolerans F2 has the application potential to improve the performance in rainbow trout farming.     

Constraints on energy intake in fish: the link between diet composition, energy metabolism, and energy intake in rainbow trout

The hypothesis was tested that fish fed to satiation with iso-energetic diets differing in macronutrient composition will have different digestible energy intakes (DEI) but similar total heat production. Four iso-energetic diets (2 × 2 factorial design) were formulated having a contrast in i) the ratio of protein to energy (P/E): high (H(P/E)) vs. low (L(P/E)) and ii) the type of non-protein energy (NPE) source: fat vs. carbohydrate which were iso-energetically exchanged. Triplicate groups (35 fish/tank) of rainbow trout were hand-fed each diet twice daily to satiation for 6 weeks under non-limiting water oxygen conditions. Feed intake (FI), DEI (kJ kg(-0.8) d(-1)) and growth (g kg(-0.8) d(-1)) of trout were affected by the interaction between P/E ratio and NPE source of the diet (P<0.05). Regardless of dietary P/E ratio, the inclusion of carbohydrate compared to fat as main NPE source reduced DEI and growth of trout by ~20%. The diet-induced differences in FI and DEI show that trout did not compensate for the dietary differences in digestible energy or digestible protein contents. Further, changes in body fat store and plasma glucose did not seem to exert a homeostatic feedback control on DEI. Independent of the diet composition, heat production of trout did not differ (P>0.05). Our data suggest that the control of DEI in trout might be a function of heat production, which in turn might reflect a physiological limit related with oxidative metabolism.     

Hilyses®, fermented Saccharomyces cerevisiae, enhances the growth performance and skin non-specific immune parameters in rainbow trout (Oncorhynchus mykiss)

Effects of Hilyses^®, fermented Saccharomyces cerevisiae (S. cerevisiae), on growth, body composition and skin mucus immune components in rainbow trout were quantified. Ninety rainbow trout (105 ± 5 g) were randomly assigned to 2 groups in triplicates and fed dietary Hilyses^® (5 g kg^?1) or control diet without Hilyses^® for 50 days. Results of this study demonstrated that growth performance increased significantly by the dietary yeast supplement; however body composition was not affected in treatment group. At the 45th and 50th day of feeding trial, results of mucus samples demonstrated that yeast supplementation in treatment group significantly promoted enzyme activities, namely lysozyme, protease, alkaline phosphatase and esterase compared to control group. Significant increases were also observed in hemagglutination and antibacterial activity against Yersinia ruckeri in fish fed treatment diet. The present study suggests that fermented S. cerevisiae may effectively promote the growth performance and skin non-specific immune parameters in rainbow trout.