Effects Of Dietary Arginine, Lysine And Threonine On Growth, Metabolism And Immune Responses Of Juvenile Darkbarbel Catfish (Pelteobagrus Vachelli)

Feeding trials were conducted to investigate the effects of arginine, threonine and the interactions of arginine and lysine on the growth, metabolism and immune responses of juvenile darkbarbel catfish. The experiments were conducted in indoor flowing culture system. Results of the present study are presented as follows: 1 A 10-week feeding trial was conducted to estimate dietary arginine requirement of juvenile darkbarbel catfish, and its effects on nonspecific immune responses and disease resistance when challenged with Aeromonas hydrophila. Six diets (each with 42.6% crude protein and 10.0% crude lipid) were formulated with grade levels of arginine (3.19, 3.72, 4.31, 4.83, 5.49 and 6.16 % of dietary protein). Each diet was fed to triplicate groups of darkbarbel catfish (initial body weight: 1.02±0.01 g) to apparent satiation and each group was stocked with 50 fish. After the feeding trial, growth, biochemical and nonspecific immune parameters were monitored. The survival rate was significantly higher in fish fed the supplemented diet compared with the unsupplemented group (3.19% of dietary protein) (P<0.05). With the increase of dietary arginine, the specific growth rate (SGR) of darkbarbel catfish increased and then reached a plateau. The arginine requirement of juvenile darkbarbel catfish based on SGR is 5.17% of dietary protein The respiratory burst activity and phagocytosis percentage (PP) of headkidney macrophages increased significantly with the increase of arginine (P<0.05). Serum lysozyme activity was significantly (P<0.05) higher in fish fed with 5.49% dietary protein than that in other groups. However, there were no significant differences in Nitric Oxide Synthase (NOS) in liver and serum. The challenge experiment with Aeromonas hydrophila also showed no difference among groups (P>0.05). It can be concluded that arginine supplementation had benefits on enhancing immune responses. 2 An 8-week feeding trial was conducted to estimate the effects of dietary arginine (Arg) and lysine (Lys) on growth and non-specific immune responses of juvenile darkbarbel catfish. Nine diets (42% crude protein and 10% crude lipid) were formulated to contain three Arg levels (2.41, 4.86 and 6.81% of dietary protein), and each with three Lys levels (1.95, 5.84 and 8.27% of dietary protein). Each diet was randomly fed to triplicate groups of darkbarbel catfish (initial body weight: 2.12±0.01 g) to apparent satiation and each group was stocked with 30 fish. At the termination of the feeding trial, growth and non-specific immune parameters were monitored. The results showed dietary arginine and lysine had significant effects on the specific growth rate (SGR) and the respiratory burst activity of headkidney macrophages of juvenile darkbarbel catfish (P<0.05). The appreciate content of diet arginine/lysine was 6.81/5.84% dietary protein based on the growth , but the respiratory burst activity of headkidney macrophages was the highest when arginine/lysine was 4.86/8.27 dietary protein. Dietary Arg had significant effects on the serum nitricoxide synthase (NOS) activity of juvenile darkbarbel catfish (P<0.05). The activity of NOS was higher in fish fed appropriate or high Arg levels than low Ary levels. No significant differences were found in the serum arginase (ARG) and catalase (CAT) (P>0.05) among dietary treatments. In the present study, significant interactions of dietary arginine and lysine were found on growth of juvenile darkbarbel catfish, but no on the body composition, hepatosomatic index (HSI), and serum NOS, ARG and CAT activity.3 An 8-week feeding trial was conducted to estimate dietary threonine requirement of juvenile darkbarbel catfish, and its effects on immune responses and metabolic indicators. Six diets (each with 39.3% crude protein and 10.6% crude lipid) were formulated with grade levels of threonine (1.84, 2.56, 3.29, 4.00, 4.76 and 5.52 % dietary protein). Each diet was randomly fed to triplicate groups of darkbarbel catfish (initial body weight: 2.12±0.01 g) to apparent satiation and each group was stocked with 30 fish. After the feeding trial, growth, immune and metabolic parameters were monitored. The results showed that, with the increase of dietary arginine, the specific growth rate (SGR) of darkbarbel catfish increased and then reached a plateau. The threonine requirement of juvenile darkbarbel catfish based on SGR is 3.25% dietary protein. The activity of threonine dehydrogenase in liver increased with the increase of threonine, and the activity in highest level of threonine (diet 6) was significantly higher than the control group (P<0.05). However, with the increase of threonine, the activity of threonine dehydrase in liver decreased and no significant differences were found among groups (P>0.05). There were no significant differences in pepsin, amylase, threonine dehydrogenase and threonine dehydrase activities in serum (P>0.05). The same were found in IgM and albumin in serm (P>0.05).