Determination of relative protein degradation activity at different life stages in rainbow trout (Oncorhynchus mykiss)

Dietary carbohydrate-to-protein ratio influences growth performance, hepatic health and dynamic of gut microbiota in atlantic salmon (Salmo salar)

Atlantic salmon (Salmo salar) fed a carbohydrate-rich diet exhibit suboptimal growth performance, along with other metabolic disturbances. It is well known that gut microbes play a pivotal role in influencing metabolism of the host, and these microbes can be modified by the diet. The main goal of the present study was to determine the effect of feeding graded levels of digestible carbohydrates to Atlantic salmon on the distal intestine digesta microbiota at 3 sampling times (i.e., weeks 4, 8 and 12), during a 12-week trial. A low carbohydrate-to-high protein diet (LC/HP, 0% wheat starch), a medium carbohydrate-to-medium protein diet (MC/MP, 15% wheat starch) or a high carbohydrate-to-low protein diet (HC/LP, 30% wheat starch) was fed to triplicate fish tanks (27 to 28 fish per tank). We performed an in-depth characterization of the distal intestine digesta microbiota. Further, growth parameters, liver histology and the expression of genes involved in hepatic neolipogenesis in fish were measured. Fish fed a HC/LP diet showed greater hepatosomatic and viscerosomatic indexes (P = 0.026 and P = 0.018, respectively), lower final weight (P = 0.005), weight gain (P = 0.003), feed efficiency (P = 0.033) and growth rate (P = 0.003) compared with fish fed the LC/HP diet. Further, feeding salmon a high digestible carbohydrate diet caused greater lipid vacuolization, steatosis index (P = 0.007) and expression of fatty acid synthase (fas) and delta-6 fatty acyl desaturase (d6fad) (P = 0.001 and P = 0.001, respectively) in the liver compared with fish fed the LC/HP diet. Although, the major impact of feeding a carbohydrate-rich diet to Atlantic salmon in beta diversity of distal intestine digesta microbiota was observed at week 4 (HC/LP vs MC/MP and HC/LP vs LC/HP; P = 0.007 and P = 0.008, respectively) and week 8 (HC/LP vs MC/MP; P = 0.04), no differences between experimental groups were detected after 12 weeks of feeding. Finally, at the end of the trial, there was a negative correlation between lactic acid bacteria (LAB) members, including Leuconostoc and Lactobacillus, with hepatic steatosis level, the hepatosomatic and viscerosomatic indexes as well as the expression of fas and d6fad. Weissella showed negative correlation with hepatic steatosis level and the hepatosomatic index. Finally, further research to explore the potential use of LAB as probiotics to improve liver health in carnivorous fish fed fatty liver-induced diet is warranted.

Seasonal Pattern of the Effect of Slurry Ice during Catching and Transportation on Quality and Shelf Life of Gilthead Sea Bream

The objective of the present study was the evaluation of the effect of slurry ice, as an alternative cooling medium during harvesting and transportation, on the quality parameters (e.g., microbiological stability, sensory attributes, physicochemical changes) and shelf life of fish. The effect of seasonal variability of seawater temperature on fish preservation using the tested cooling media was also investigated. Gilthead sea bream (Sparus aurata) was slaughtered and transported in different mixtures of conventional flake ice and slurry ice for 24 h. Three mixtures of ice were tested as T: slaughtered in flake ice and transported in flake ice (control), TC: slaughtered in slurry ice and transported in flake ice, T50: slaughtered and transported in slurry ice 50%–flake ice 50%. Samples were subsequently stored isothermally at 0 °C for shelf-life evaluation. Three independent experiments were performed at three different periods, i.e., January, April, and September, referring to a sea water temperature range of 13.3–26.8 °C. Higher sea water temperatures at catching led to lower microbial growth rates and proteolytic enzyme activities and longer shelf life of refrigerated whole fish. The partial replacement of conventional flake ice with slurry ice improved the quality and extended the shelf life of fish at 0 °C by 2–7 days. The results of the study support that the use of slurry ice may enable better quality maintenance and significant shelf-life extension of whole gilthead sea bream.

Fermented Soybean Meal Increases Lactic Acid Bacteria in Gut Microbiota of Atlantic Salmon (Salmo salar)

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.

Activity of metabolic enzymes and muscle-specific gene expression in parr and smolts Atlantic salmon Salmo salar L. of different age groups

This study was conducted to characterize the energy metabolism level and the features of muscle growth regulation during the development of Atlantic salmon (Salmo salar) inhabiting the Indera River (Kola Peninsula, Russia). The activities of aerobic and anaerobic enzymes (cytochrome c oxidase and lactate dehydrogenase) and carbohydrate metabolism enzymes (glucose-6-phosphate dehydrogenase, glycerol-3-phosphate dehydrogenase, and aldolase) were measured in muscle and liver tissue. Gene expression levels of myosin heavy chain (MyHC), myostatin (MSTN-1a), and myogenic regulatory factors (MRFs-MyoD1a, MyoD1b, MyoD1c, Myf5, myogenin) were measured in the white muscles of salmon parr of ages 0+, 1+, 2+, and 3+ and smolts of ages 2+ and 3+. Multidirectional changes in the activity of enzymes involved in aerobic and anaerobic energy metabolism with age were shown in the white muscles of the parr. The cytochrome c oxidase activity was higher in muscles of underyearlings (0+) and yearlings (1+) and decreased in 2+ and 3+ age groups. The activity of lactate dehydrogenase, in contrast, increased with age. The patterns of changes in expression levels of MyoD1a, MyoD1b, myogenin, MyHC, and MSTN-1a at different ages of the parr were similar. Particularly, the expression of these genes peaked in the yearling parr (1+) and then decreased in elder groups. The differences were revealed in parameters studied between the parr and smolts. The level of aerobic and anaerobic metabolism enzyme activities was higher in the white muscles of smolts than in parr. The activity of carbohydrate metabolism enzymes was decreased in the smolts' livers. The expression levels of MyHC, MyoD1a, MyoD1b, and myogenin were lower in smolts at age 2+ compared to parr. These findings expand our knowledge of age-related and stage-related features of energy metabolism and muscle development regulation in young Atlantic salmon in their natural habitat. The results might be used for monitoring of the salmon population during restoration and rearing.

Protein degradation systems in the skeletal muscles of parr and smolt Atlantic salmon Salmo salar L. and brown trout Salmo trutta L

Although protein degradation limits the rate of muscle growth in fish, the role of proteolytic systems responsible for degrading myofibrillar proteins in skeletal muscle is not well defined. The study herein aims to evaluate the role of calpains (calcium-activated proteases) and proteasomes (ATP-dependent proteases) in mediating muscle protein turnover at different life stages in wild salmonids. Protease activities were estimated in Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) parr and smolts from the Indera River (Kola Peninsula, Russia). Calpain and proteasome activities in Atlantic salmon skeletal muscles were lower in smolts as compared with parr. Reduced muscle protein degradation accompanying Atlantic salmon parr-smolt transformation appeared to provide intense muscle growth essential for a minimum threshold size achievement that is required for smoltification. Calpain and proteasome activities in brown trout parr and smolts at age 3+ did not significantly differ. However, calpain activity was higher in smolts brown trout 4+ as compared with parr, while proteasome activity was lower. Results suggest that brown trout smoltification does not correspond with intense muscle growth and is more facultative and plastic in comparison with Atlantic salmon smoltification. Obtained data on muscle protein degradation capacity as well as length-weight parameters of fish reflect differences between salmon and trout in growth and smoltification strategies.

[Intracellular Protein Degradation in Growth of Atlantic Salmon, Salmo salar L]

A brief review on the common characteristics and specific features of proteolytic machinery in fish skeletal muscles (based on Atlantic salmon, Salmo salar L., Salmonidae) has been given. Among a variety of proteases in the muscle tissue, those determining protein degradation level in developing and intensively growing muscles in salmon young and by this way regulating protein retention intensity and growth at all namely lysosomal cathepsins B and D and calcium-dependent proteases (calpains) were comprehensively studied. Revealed age-related differences in intracellular protease activity in salmon skeletal muscles indicate the role of proteolysis regulation in growth in general and a specific role of the individual proteolytic enzymes in particular. The data on negative correlation of cathepsin D and calpain activity levels in muscles and the rate of weight increase in juvenile salmon were obtained. A revealed positive correlation of cathepsin B activity and morphometric parameters in fish young presumably indicates its primary contribution to non-myofibrillar protein turnover.

Dietary methionine level affects growth performance and hepatic gene expression of GH-IGF system and protein turnover regulators in rainbow trout (Oncorhynchus mykiss) fed plant protein-based diets

The effects of dietary level of methionine were investigated in juvenile rainbow trout (Oncorhynchus mykiss) fed five plant-based diets containing increasing content of crystalline methionine (Met), in a six week growth trial. Changes in the hepatic expression of genes related to i) the somatotropic axis: including the growth hormone receptor I (GHR-I), insulin-like growth hormones I and II (IGF-I and IGF-II, respectively), and insulin-like growth hormone binding protein-1b (IGFBP-1b); and ii) protein turnover: including the target of rapamycin protein (TOR), proteasome 20 delta (Prot 20D), cathepsin L, calpains 1 and 2 (Capn 1 and Capn 2, respectively), and calpastatin long and short isoforms (CAST-L and CAST-S, respectively) were measured for each dietary treatment. The transcript levels of GHR-I and IGF-I increased linearly with the increase of dietary Met content (P<0.01), reflecting overall growth performances. The apparent capacity for hepatic protein degradation (derived from the gene expression of TOR, Prot 20D, Capn 1, Capn 2, CAST-L and CAST-S) decreased with increasing dietary Met level in a relatively linear manner. Our results suggest that Met availability affects, directly or indirectly, the expression of genes involved in the GH/IGF axis response and protein turnover, which are centrally involved in the regulation of growth.

Inflammatory responses in primary muscle cell cultures in Atlantic salmon (Salmo salar)

BACKGROUND

The relationship between fish health and muscle growth is critical for continued expansion of the aquaculture industry. The effect of immune stimulation on the expression of genes related to the energy balance of fish is poorly understood. In mammals immune stimulation results in major transcriptional changes in muscle, potentially to allow a reallocation of amino acids for use in the immune response and energy homeostasis. The aim of this study was to investigate the effects of immune stimulation on fish muscle gene expression.

RESULTS

Atlantic salmon (Salmo salar) primary muscle cell cultures were stimulated with recombinant (r)IL-1β, a major proinflammatory cytokine, for 24 h in order to simulate an acute immune response. The transcriptomic response was determined by RNA hybridization to a 4 × 44 K Agilent Atlantic salmon microarray platform. The rIL-1β stimulation induced the expression of genes related to both the innate and adaptive immune systems. In addition there were highly significant changes in the expression of genes related to regulation of the cell cycle, growth/structural proteins, proteolysis and lipid metabolism. Of interest were a number of IGF binding proteins that were differentially expressed, which may demonstrate cross talk between the growth and immune systems.

CONCLUSION

We show rIL-1β modulates the expression of not only immune related genes, but also that of genes involved in processes related to growth and metabolism. Co-stimulation of muscle cells with both rIGF-I and rIL-1β demonstrates cross talk between these pathways providing potential avenues for further research. This study highlights the potential negative effects of inflammation on muscle protein deposition and growth in fish and extends our understanding of energy allocation in ectothermic animals.

[Proteases of calpain family in water invertebrates and fish]

The activity of Ca2+-dependent proteases, or calpains (EC 3.4.22.17), in a wide range of aquatic invertebrates (Oligochaeta, Hirudinea, Crustacea, Insecta, Gastropoda, Bivalvia) and vertebrates (Osteichthyes) was estimated. Detected molecular properties ofcalpains from the tissues of different species allow considering the complication of their structural organization and regulatory mechanisms between invertebrates and vertebrates in comparative-evolutionary aspect. Certain conclusions can be drawn about changes in the functional role of this proteolytic system in the cell metabolism.