An 8-week feeding trial was conducted to estimate the optimum dietary protein to energy (P/E) ratio in juvenile olive £ounder Paralichthys olivaceus. Eight experimental diets were formulated with two energy levels and four protein levels at each energy level. Two energy levels of 12.5 and 16.7 kJ g À 1 diets were included at crude protein (CP) levels of 25%, 30%, 35% and 45% with 12.5 kJ g À 1 , and CP levels of 35%, 45%, 50% and 60% with 16.7 kJ g À 1 . After 1 week of the conditioning period, ¢sh initially averaging 8.1 AE 0.08 g (mean AE SD) were randomly distributed into the aquarium as groups of 15 ¢sh. Each diet was fed on a dry-matter basis to ¢sh in three randomly selected aquariums at a rate of 3^5% of total wet body weight per day for 8 weeks.After 8 weeks of the feeding trial, weight gain (WG), feed e⁄ciency ratio and speci¢c growth rate of ¢sh fed 45% CP with16.7 kJ g À 1 energy diet were sig-ni¢cantly higher than those from the other dietary treatments (Po0.05). WG of ¢sh fed 12.5 kJ g À 1 energy diets increased with the increase of dietary protein levels. However,WG of ¢sh fed 16.7 kJ g À 1 energy diets increased with the increase of dietary protein levels up to 45% CP and then decreased when ¢sh fed 50% and 60% CP diets. Both dietary protein and energy a¡ected protein retention e⁄ciency and energy retention e⁄ciency. Haemoglobin (Hb) of ¢sh fed 35% and 45% CP diets with 12.5 kJ g À 1 energy were signi¢cantly high and not di¡erent from Hb of ¢sh fed 45% and 50% CP diets with 16.7 kJ g À 1 energy. Haematocrit of ¢sh fed 45% CP diet with 16.7 kJ g À 1 energy was signi¢cantly higher than those from ¢sh fed 25% and 30% CP diets with 12.5 kJ g À 1 energy (Po 0.05). Based on the results of this experiment, we concluded that the optimum dietary P/E ratio was 27.5 mg protein kJ À 1 with diet containing 45% CP and16.7 kJ g À 1 energy in juvenile olive £ounder. Aquaculture Research, 2004, 35, 250^255 250 r 2004 Blackwell Publishing Ltd ZnSO 4 Á 7H 2 O, 21.9; Fe-citrate, 29.6; Ca-lactate, 303.89; AlCl 3 Á 6H 2 O, 0.15; KIO 3 , 0.15; Na 2 Se 2 O 3 , 0.01; CuCl 2 , 0.2; MnSO 4 Á H 2 O, 2.0; CoCl 2 Á 6H 2 O, 1.0. Aquaculture Research, 2004, 35, 250^255 Optimum dietary P/E ratio in £ounder K-W Kim et al.

To investigate the potential synergistic effects of dietary ascorbic acid (AA), α‐tocopheryl acetate (TA) and selenium (Se) supplementation above minimum requirement levels on the growth performance and disease challenge of fingerling Nile tilapia, Oreochromis niloticus L., five experimental diets were formulated: control (150 mg AA, 100 mg TA and 0.2 mg Se per kg diet), excessive ascorbic acid (eAA) (2000 mg AA, 100 mg TA and 0.2 mg Se per kg diet), excessive α‐tocopheryl acetate (eTA) (150 mg AA, 240 mg TA and 0.2 mg Se per kg diet), excessive selenium (eSe) (150 mg AA, 100 mg TA and 0.5 mg Se per kg diet) and excessive all (eALL) (2000 mg AA, 240 mg TA and 0.5 mg Se per kg diet). Experimental fish averaging 2.9 were randomly distributed in each aquarium as a group of 40 fish with total weight 116±2.9 g (mean±SD). Each diet was fed on a dry‐matter basis to fish in three randomly selected aquaria at a rate of 4–8% of total body weight daily. After 10 weeks of the feeding trial, fish fed eAA, eTA and eALL diets had significantly higher weight gain, feed efficiency ratio, protein efficiency ratio and specific growth rate than fish fed eSe and control diets (P<0.05). There was no significant difference among fish fed five experimental diets in cumulative mortalities when fish were challenged with Edwardsiella tarda at the end of the experimental period. These results indicate that sufficient supplementation of dietary AA or TA had positive effects on growth performance, but there was no synergistic effect of excessive dietary AA, TA and Se supplementation on growth performance and disease resistance to E. tarda in fingerling Nile tilapia.

This study evaluated the dietary lysine requirement by measuring the plasma free lysine concentrations in rainbow trout, Oncorhynchus mykiss after dorsal aorta cannulation. A basal diet containing 36.6 % crude protein (29.6 % crystalline amino acids mixture, 5 % casein and 2 % gelatin) was formulated to one of the seven L-amino acid based diets containing graded levels of lysine (0.72, 1.12, 1.52, 1.92, 2.32, 2.72 or 3.52 % dry diet). A total of 35 fish averaging 512 ± 6.8 g (mean ± SD) were randomly distributed into seven groups with five fish in each group. After 48 h of feed deprivation, each group of fish was fed one of the experimental diets by intubation at 1 % body weight. Blood samples were taken at 0, 5 and 24 h after intubation. Post-prandial plasma free lysine concentrations (PPlys, 5 h after intubation) of fish fed diets containing ≥ 2.32 % lysine were higher than those of fish fed diets containing ≤ 1.92 % lysine. Post-absorptive free lysine concentrations (PAlys, 24 h after intubation) of fish fed diets containing 2.32 and 3.52 % lysine were higher than those of fish fed diets containing ≤ 1.52 % lysine. The brokenline regression analysis on the basis of PPlys and PAlys indicated that the lysine requirement of rainbow trout could be 2.34 and 2.20 % in diet. Therefore, these results strongly suggested that the dietary lysine requirement based on the broken-line model analyses of PPlys and PAlys could be greater than 2.2 but less than 2.34 % (corresponding to be 6.01 % ≤, but ≤ 6.39 % in dietary protein basis, respectively) in rainbow trout. Also, these results shown that the quantitative estimation of lysine requirement by using PPlys and PAlys could be an acceptable method in fish.

Three experiments were conducted to determine the effects of dietary arginine concentrations on plasma free amino acid (PAA) concentrations in rainbow trout, Oncorhynchus mykiss (Walbaum). The first experiment was conducted to determine appropriate post-prandial and food deprivation sampling times in dorsal aorta cannulated rainbow trout averaging 519±9.5 g (mean±SD) at 16°C. Blood samples were taken at 0, 2, 3, 4, 5, 6 and 24 h after feeding (0 and 24 h blood samples were taken from the same group of fish). PAA concentrations increased by 2 h post-feeding and the concentration of all essential amino acids except histidine peaked at 5 h and returned to 0 time values by 24 h. In the second experiment dorsal aorta cannulated rainbow trout averaging 528±11.3 g (mean±SD) were divided into 6 groups of 4 fish to study the effect of dietary arginine levels on PAA. After 24 h food deprivation, each group of fish was fed one of six L-amino acid diets containing graded levels of arginine (0.48, 1.08, 1.38, 1.68, 1.98 or 2.58%) by intubation. Blood samples were taken at 0, 5 and 24 h after feeding. Post-prandial (5 h after feeding) plasma-free arginine concentrations (PParg) showed a breakpoint at 1.03% arginine in the diet and post-absorptive (24 h after feeding) plasma free-arginine concentrations (PAarg) showed a breakpoint at 1.38% arginine. PAarg increased linearly from fish fed diets containing arginine between 0.48% and 1.38%, and the concentrations remained constant from fish fed diets containing arginine at or above 1.38%, but were all below PParg at all time points. Results of the third experiment confirm the results that PParg concentrations from fish fed arginine deficient diets were higher than PAarg (0 or 24 h values). Thus, in contrast to mammals and birds, the PParg when arginine is present in the diet as the most limiting amino acid such that it severely limits growth, increases in plasma rather than decreases.

This study was carried out to evaluate the dietary threonine requirement by measuring the plasma free threonine and ammonia concentrations in rainbow trout, Oncorhynchus mykiss after dorsal aorta cannulation. A total of 70 fish (average initial weight 506±8.2 g) were randomly distributed into each of the 14 net cages (5 fish/cage). After 48 hours (h) of feed deprivation, each group was intubated at 1% body weight with one of the seven L-amino acid based diets containing graded levels of threonine (0.42%, 0.72%, 0.92%, 1.12%, 1.32%, 1.52%, or 1.82% of diet, dry matter basis). Blood samples were taken at 0, 5, and 24 h after intubation. Post-prandial plasma free threonine concentrations (PPthr) of fish 5 h after intubation with diets containing 1.32% or more threonine were significantly higher than those of fish intubated with diets containing 1.12% or less threonine (p<0.05). Post-absorptive free threonine concentrations (PAthr) after 24 h of intubation of the fish with diets containing 0.92% or more threonine were significantly higher than those of fish intubated with diets containing 0.72% or less threonine. Post-prandial plasma ammonia concentrations (PPA, 5 h after intubation) were not significantly different among fish intubated with diets containing 1.12% or less threonine, except the PPA of fish intubated with diet containing 0.42% threonine. Broken-line model analyses of PPthr, PAthr, and PPA indicated that the dietary threonine requirement of rainbow trout should be between 0.95% (2.71) and 1.07% (3.06) of diet (% of dietary protein on a dry matter basis).