Impact of early-life rearing history on gut microbiome succession and performance of Nile tilapia

BackgroundFish gut microbial colonisation starts during larval stage and plays an important role in host’s growth and health. To what extent first colonisation could influence the gut microbiome succession and growth in later life remains unknown. In this study, Nile tilapia embryos were incubated in two different environments, a flow-through system (FTS) and a biofloc system (BFS); hatched larvae were subsequently cultured in the systems for 14 days of feeding (dof). Fish were then transferred to one common recirculating aquaculture system (RAS1, common garden, 15–62 dof), followed by a growth trial in another RAS (RAS2, growth trial, 63–105 dof). In RAS2, fish were fed with two types of diet, differing in non-starch polysaccharide content. Our aim was to test the effect of rearing environment on the gut microbiome development, nutrient digestibility and growth performance of Nile tilapia during post-larvae stages.ResultsLarvae cultured in the BFS showed better growth and different gut microbiome, compared to FTS. After the common garden, the gut microbiome still showed differences in species composition, while body weight was similar. Long-term effects of early life rearing history on fish gut microbiome composition, nutrient digestibility, nitrogen and energy balances were not observed. Still, BFS-reared fish had more gut microbial interactions than FTS-reared fish. A temporal effect was observed in gut microbiome succession during fish development, although a distinct number of core microbiome remained present throughout the experimental period.ConclusionOur results indicated that the legacy effect of first microbial colonisation of the fish gut gradually disappeared during host development, with no differences in gut microbiome composition and growth performance observed in later life after culture in a common environment. However, early life exposure of larvae to biofloc consistently increased the microbial interactions in the gut of juvenile Nile tilapia and might possibly benefit gut health

Effect of type of dietary non-protein energy source (starch vs. fat) on the body bile acid pool size and composition, faecal bile acid loss and bile acid synthesis in rainbow trout (Oncorhynchus mykiss)

Effects of the type of dietary non-protein energy source on the size and composition of the total body bile acid pool, on faecal bile acid loss and on bile acid synthesis were investigated in rainbow trout. Two diets were formulated (similar DP:DE ratio) that differed in the inclusion of either maize starch (Starch) or rapeseed oil (Fat) as main non-protein source. Fish were fed to satiation for 44 days. Type of non-protein energy source did not substantially affect the body bile acid pool composition. However, feeding the Starch diet resulted in a larger total body bile acid pool size compared with the Fat diet, and this despite enhanced faecal bile acid loss when feeding the Starch diet that was related to more faeces being produced. Bile acid synthesis in fish fed the Starch diet was more than two times higher compared with fish fed the Fat diet. The difference in body bile acid pool size between diets suggests upregulation of bile acid synthesis in fish fed the Starch diet beyond the level needed to compensate for the higher faecal bile acid loss and/or downregulation of bile acid synthesis in fish fed the Fat diet. The underlying mechanisms for this difference in synthesis need further investigation.</p

Impact of dietary glutamate and glycine on growth and nutrient utilization in rainbow trout (Oncorhynchus mykiss)

A feeding trial was conducted to test the effect of dietary glutamate and glycine supplementation on growth potential, nutritional utilization and digestion, and energy metabolism of rainbow trout (Oncorhynchus mykiss). Four isonitrogenous and isolipidic diets (2 × 2 factorial design) were formulated with glutamate (Glu) and glycine (Gly) as the main factors. The protein source consisted mainly of black soldier fly larvae meal (40% inclusion in all diets) for its low-level content of glutamate and glycine. Triplicate groups of rainbow trout (30 fish/tank with mean initial body weight of 87.5 g ± 0.9) were restrictively fed by hand twice a day for 6 weeks. Dietary Glu and Gly supplementation did not affect feed intake, specific growth rate, or the feed conversion ratio. Whole body protein, lipid, amino acid and fatty acid composition were also unaffected by the supplementation of Glu and Gly in the diets. Dietary Gly supplementation increased the apparent digestibility of amino acids. Furthermore, supplementation with Gly, increased the concentration of serine, glycine, tryptophane, tyrosine and citrulline, while supplementation with Glu in the diets increased the concentration of hydroxy-proline and β-alanine in the serum of rainbow trout. Both dietary Glu and Gly supplementation improved the digestibility of the fatty acids. The expression of genes involved in the hepatic bile acid synthesis (e.g., apical sodium dependent bile acid transporter and organic solute transporter) were affected by supplementation of Gly in the diets. In general, this study showed that dietary supplementation with Gly and Glu improved the nutrient digestibility in rainbow trout

The effect of low pH on physiology, stress status and growth performance of turbot (Psetta maxima L.) cultured in recirculating aquaculture systems

We evaluated the effect of low pH and low and high total ammonia nitrogen (TAN) concentrations on the physiology, stress status and the growth performance of turbot in RAS. Two experiments were conducted. In Experiment 1, turbot (466 g) were grown at control (pH 7.5; TAN ~0.5 mg/L) or low pH and high TAN (pH 5.7; TAN ~50 mg/L) for 55 days. In Experiment 2, turbot (376 g) were grown at control (pH 7.5; TAN ~0.5 mg/L), low pH and low TAN (pH 5.7; TAN ~5 mg/L) or low pH and high TAN (pH 5.7; TAN ~50 mg/L) for 59 days. In Experiment 1, final body weight, feed intake and growth were significantly lower and FCR significantly higher in turbot exposed to low pH and high TAN. In Experiment 2, only growth was significantly lower in turbot exposed to treatment low pH and high TAN as compared to fish in the control treatment and low pH and low TAN. Osmoregulation and stress indicators measured were within normal levels. In conclusion, turbot grew equally well in a water pH of 7.5 or 5.7 provided a low TAN. In contrast, low pH combined with a high TAN impaired turbot performance.</p

Effects of demand-feeding and dietary protein level on nitrogen metabolism and symbiont dinitrogen gas production of common carp (Cyprinus carpio, L.)

Ammonia accumulation is a major challenge in intensive aquaculture, where fish are fed protein-rich diets in large rations, resulting in increased ammonia production when amino acids are metabolized as energy source. Ammonia is primarily excreted via the gills, which have been found to harbor nitrogen-cycle bacteria that convert ammonia into dinitrogen gas (N2) and therefore present a potential in situ detoxifying mechanism. Here, we determined the impact of feeding strategies (demand-feeding and batch-feeding) with two dietary protein levels on growth, nitrogen excretion, and nitrogen metabolism in common carp (Cyprinus carpio, L.) in a 3-week feeding experiment. Demand-fed fish exhibited significantly higher growth rates, though with lower feed efficiency. When corrected for feed intake, nitrogen excretion was not impacted by feeding strategy or dietary protein, but demand-fed fish had significantly more nitrogen unaccounted for in the nitrogen balance and less retained nitrogen. N2 production of individual fish was measured in all experimental groups, and production rates were in the same order of magnitude as the amount of nitrogen unaccounted for, thus potentially explaining the missing nitrogen in the balance. N2 production by carp was also observed when groups of fish were kept in metabolic chambers. Demand feeding furthermore caused a significant increase in hepatic glutamate dehydrogenase activities, indicating elevated ammonia production. However, branchial ammonia transporter expression levels in these animals were stable or decreased. Together, our results suggest that feeding strategy impacts fish growth and nitrogen metabolism, and that conversion of ammonia to N2 by nitrogen cycle bacteria in the gills may explain the unaccounted nitrogen in the balance

Effect of early life hypoxia and diet composition on growth, feed intake and oxygen consumption of rainbow trout (Oncorhynchus mykiss) in later life

Session Nutrition: Physiology and RequirementsEffect of early life hypoxia and diet composition on growth, feed intake and oxygen consumption of rainbow trout (Oncorhynchus mykiss) in later life. Aquaculture Europe 201

Nutrient mineralization and organic matter reduction performance of RAS-based sludge in sequential UASB-EGSB reactors

There is a recognized need for mineralizing aquaculture-derived sludge in aquaponics systems in order to reduce waste production. Many recent studies of aquacultural waste treatment have focused only the production of biogas as opposed to the potential for mineralization of nutrient-rich sludge. Upflow anaerobic sludge blanket (UASB) reactors provide one possible solution for breaking down sludge into bioavailable nutrients that can subsequently be delivered to plants. As such, this study examines the mineralization performance of sequential UASB reactors that are designed with an expanded granular sludge bed (EGSB) and compared to standard aerobic and anaerobic batch reactors. Results of our experiments demonstrate that only chemical oxygen demand reduction is significantly different. An unexpected drop in pH of one of the three reactor systems revealed that a pH below 6 was able to significantly increase the mineralization and mobilization of nutrients. Approximately 25% of phosphorus, potassium, and calcium could also be recovered from the sludge under lower pH conditions, as compared to the mineralization performance of standard UASB reactors running at a higher pH. However, the opposite effect was observed with respect to organic sludge reduction, where diminished performance was observed in the low-pH reactor. The current study implies that anaerobic reactors operating at low pH can potentially contribute towards improved nutrient recovery in multi-loop aquaponics systems and reduction of additive agents for pH control of the hydroponic subsystem.</p