Requirement for tryptophan by milkfish (Chanos chanos Forsskal) juveniles

Dietary tryptophan affects growth performance, digestive and absorptive enzyme activities, intestinal antioxidant capacity, and appetite and GH-IGF axis-related gene expression of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂)

The 56-day feeding trial was carried out to investigate the effects of dietary tryptophan (Trp) on growth performance, digestive and absorptive enzyme activities, intestinal antioxidant capacity, and appetite and GH-IGF axis-related genes expression of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂). A total of 864 hybrid catfish (21.82 ± 0.14 g) were fed six different experimental diets containing graded levels of Trp at 2.6, 3.1, 3.7, 4.2, 4.7, and 5.6 g kg^-1 diet. The results indicated that dietary Trp increased (P < 0.05) (1) final body weight, percent weight gain, specific growth rate, feed intake, feed efficiency, and protein efficiency ratio; (2) fish body protein, lipid and ash contents, protein, and ash production values; (3) stomach weight, stomach somatic index, liver weight, intestinal weight, length and somatic index, and relative gut length; and (4) activities of pepsin in the stomach; trypsin, chymotrypsin, lipase, and amylase in the pancreas and intestine; and γ-glutamyl transpeptidase, Na⁺, K⁺-ATPase, and alkaline phosphatase in the intestine. Dietary Trp decreased malondialdehyde content, increased antioxidant enzyme activities and glutathione content, but downregulated Keap1 mRNA expression, and upregulated the expression of NPY, ghrelin, GH, GHR, IGF1, IGF2, IGF1R, PIK3Ca, AKT1, TOR, 4EBP1, and S6K1 genes. These results indicated that Trp improved hybrid catfish growth performance, digestive and absorptive ability, antioxidant status, and appetite and GH-IGF axis-related gene expression. Based on the quadratic regression analysis of PWG, SGR, and FI, the dietary Trp requirement of hybrid catfish (21.82-39.64 g) was recommended between 3.96 and 4.08 g kg^-1 diet (9.4-9.7 g kg^-1 of dietary protein).

Effect of dietary L-tryptophan on the survival, immune response and gut microbiota of the Chinese mitten crab, Eriocheir sinensis

This study investigated the influence of L-tryptophan (L-trp) on the survival, immune response and gut microbiota of the Chinese mitten crab, Eriocheir sinensis (with an average weight of 16.58 ± 2.20 g). After 30 days of feeding with diets supplemented with L-trp at 0.36%, 0.47%, 0.73% and 1.05% (groups 1, 2, 3 and 4, respectively), the survival rate and bacterial challenge (Aeromonas hydrophila) were evaluated, the activities of antioxidant and phosphatase enzymes in the serum were assessed, and the gut microbiota were measured via high-throughput Illumina sequencing. The results showed that the supplementation of L-trp significantly improved the survival rate of crabs (P < 0.05). After feeding for 7 days, it was observed that a high L-trp diet significantly increase the survival rate relative to a basal diet after a 96-h post-challenge with A. hydrophila (P < 0.05). The activity of CAT and AKP in the serum were increased by the addition of L-trp. The activity of CAT and AKP in the serum in group 4 were higher than those in group 1 (P < 0.05). Furthermore, we observed that adjunction of the L-trp can significantly increase the richness and diversity of the gut microbiota. The dominant phylum in the intestine of the Chinese mitten crab were Tenericutes, Proteobacteria, Firmicutes, Chloroflexi and Actinobacteria. The L-trp in the diets increased the richness of Proteobacteria, Firmicutes and Actinobacteria in the intestine significantly. These bacteria were all dominant bacteria and had a specific role in promoting the immunity of E. sinensis. Therefore, it could be inferred that L-trp supplementation is beneficial in the diet of E. sinensis. Based in these results, the dietary 0.47% or 0.73%L-trp supplemented is found to be optimum to improve E. sinensis survival.

Dietary amino acid L-tryptophan requirement of fingerling Indian catfish, Heteropneustes fossilis (Bloch), estimated by growth and haemato-biochemical parameters

An 8-week feeding trial was conducted to determine the dietary tryptophan requirement of fingerling Indian catfish, Heteropneustes fossilis (6.10 ± 1.15 cm, 4.44 ± 0.50 g). Six isonitrogenous (40 g 100 g⁻¹) and isoenergetic (17.90 kJ g⁻¹) amino acid test diets were formulated with gradation of 0.1 g 100 g⁻¹ containing graded levels of L-tryptophan (0.04-0.54 g 100 g⁻¹, dry diet). Fish were stocked in triplicate groups, in 75-L circular trough with flow-through system and fed experimental diets at 4% BW/day twice daily. Maximum live weight gain (258%), best feed conversion ratio (FCR) (1.54) and protein efficiency ratio (PER) (1.62) were obtained in fish fed diet containing 0.34 g 100 g⁻¹ tryptophan. However, quadratic regression analysis of weight gain, FCR, PER and body protein deposition (BPD) data indicated requirements for dietary tryptophan at 0.37, 0.33, 0.32 and 0.33 g 100 g⁻¹ of dry diet, respectively. Significantly (P < 0.05) higher body protein, minimum moisture and intermediate fat contents were recorded at 0.34 g 100 g⁻¹ dietary tryptophan diet. Ash content was not significantly different (P > 0.05) among treatments except for diets 0.04 and 0.14 g 100 g⁻¹. Excellent somatic and haematological indices values were obtained at the requirement level. Based on above results, it is recommended that the diet for H. fossilis should contain tryptophan at 0.32 g 100 g⁻¹, dry diet, corresponding to 0.80 g 100 g⁻¹ dietary protein for optimum growth and efficient feed utilization.