Growth Responses of Juvenile Red Drum Sciaenops ocellatus to Dietary Phenylalanine and Tyrosine Can Be Used to Calculate the Total Aromatic Amino Acid Requirement

The Optimum Dietary Phenylalanine Requirement of Hybrid Grouper (Epinephelusfuscoguttatus ♀ × Epinepheluslanceolatus ♂) Juveniles: Effects on Growth Performance, Gut Micromorphology, and Antioxidation

The optimum phenylalanine (Phe) requirement for hybrid grouper (Epinephelusfuscoguttatus ♀ × Epinepheluslanceolatus ♂) juveniles was determined through an 8-week growth trial. A total of seven isoenergetic (340 kcal per 100 g of dry matter), isonitrogenous, and isolipidic diets were made, containing 8.2 (Phe 8.2), 9.2 (Phe 9.2), 10.1 (Phe 10.1), 11.2 (Phe 11.2), 13.3 (Phe 13.3), 15.2 (Phe 15.2), and 17.3 g/kg (Phe 17.3), respectively. Triplicate tanks of juvenile fish (about 16.7 g/fish) were fed each experimental diet twice daily until apparent satiation. The results indicated that different dietary Phe levels significantly influenced weight gain percentage (WG), feed efficiency (FE), protein efficiency ratio (PER), as well as, productive protein value (PPV). Fish fed Phe 8.2 had the lowest WG or PPV among all experimental treatments. Furthermore, the optimal dietary Phe level increased fold height, width, enterocyte, and microvillus height of fish. The Phe 10.1 group exhibited higher growth hormone (GH) expression in the pituitary compared to other groups. Expression of hepatic insulin-like growth factor-1 (IGF-1) and growth hormone receptor 1 (GHR1) displayed a similar pattern of variation to that of GH. The Phe 13.3 group had lower expression of S6 kinase 1 (S6K1) and target of rapamycin (TOR) than other groups. In addition, fish fed Phe 10.1 had lower levels of nuclear factor erythroid 2 (Nrf2) and heat shock protein 70 (HSP70) in the head kidney, and Cu/Zn-superoxide (Cu/ZnSOD) dismutases in the midgut compared to fish fed other Phe levels. Generally, optimal Phe content in the diet of hybrid grouper was estimated to be 12.7 g/kg of dry matter (27.3 g/kg of dietary protein), and at this level, the feed utilization, gut micromorphology, and immunity of fish were also elevated.

Dietary glycine supplementation enhances the growth performance of hybrid striped bass (Morone saxatilis ♀× Morone chrysops ♂) fed soybean meal-based diets

This study was conducted to test the hypothesis that supplementing 1% and 2% glycine to soybean meal (SBM)-based diets can improve the growth performance of juvenile hybrid striped bass (HSB). The basal diets contained 15% fishmeal and 58% SBM (DM basis). Alanine was used as the isonitrogenous control in different diets. All diets contained 44% crude protein and 10% lipids (DM basis). There were four tanks (15 fish per tank) per dietary group, with the mean of the initial body weight (BW) of fish being 5.3 g. Fish were fed to apparent satiation twice daily, and their BW was recorded every 2 wk. The trial lasted for 8 wk. Results indicated that the BW, weight gain, protein efficiency ratio, and retention of dietary lipids in fish were enhanced (P < 0.05) by dietary supplementation with 1% or 2% glycine. In addition, dietary supplementation with glycine did not affect (P > 0.05) the feed intake of fish but increased (P < 0.05) the retention of dietary nitrogen, most amino acids, and phosphorus in the body, compared to the 0% glycine group. Dietary supplementation with 1% and 2% glycine dose-dependently augmented (P < 0.05) the villus height of the proximal intestine and reduced the submucosal thickness of the gut, while preventing submucosal and lamina propria hemorrhages. Compared with the 0% glycine group, dietary supplementation with 1% or 2% glycine decreased (P < 0.05) the proportion of skeletal-muscle fibers with diameters of 40 to 60 µm but increased (P < 0.05) the proportion of skeletal-muscle fibers with diameters of 80 to 100 µm and > 100 µm. Collectively, these findings indicate that glycine in SBM-based diets is inadequate for maximum growth of juvenile HSB and that dietary supplementation with 1% or 2% glycine is required to improve their weight gain and feed efficiency. Glycine is a conditionally essential amino acid for this fish.

Use of deuterium oxide (2H2O) to assess muscle protein synthesis in juvenile red drum (Sciaenops ocellatus) fed complete, and valine-deficient diets

The use of ²H₂O in tank water to assess protein synthesis rates in fish is a relatively novel methodology that could allow for a better understanding of the effects of particular nutritional and environmental variables on rates of protein accretion. As such, this study involved an assessment and comparison of protein synthesis rates in the muscle of juvenile red drum fed a control diet (nutritionally complete) versus a valine (Val)-deficient diet. Six groups of 12 juvenile red drum, initially weighing ~ 4.5 g/fish, were stocked in six separate 38-L aquaria operating as a recirculating system. Fish were acclimatized to experimental conditions for 2 weeks while being fed the control diet. Just prior to initiating the protein synthesis assay, one aquarium of fish was fed the control diet while a second aquarium of fish was fed the Val-deficient diet. Immediately after consuming the experimental diets, each group of fish was moved to an independent aquarium containing ²H₂O, and the fractional synthetic rate (FSR) of protein synthesis was obtained at 12, 24, 36 and 48 h after feeding by collecting two fish per treatment at each time point. This protein synthesis assay procedure was performed in three separate sessions, and considered as replicates over time (n = 3) for fish fed the control or Val-deficient diets immediately before initiating the session. Results indicated that a one-time feeding of a diet deficient in Val significantly reduced protein synthesis rates in the muscle of red drum. In addition, a significant effect of time after feeding was found, where observed FSR values peaked at 12 h after feeding and decreased as time progressed. In conclusion, deuterium methodologies were applicable to red drum, and this approach had the sensitivity to assess differences in protein synthesis rates when dietary perturbations were introduced.