Two experiments were conducted to estimate the dietary choline requirement and to determine the effects of dietary choline on liver lipid deposition in juvenile hybrid striped bass (Monrone saxatilis x M. chrysops). Experimental diets contained 0.73 g total sulfur amino acids/100 g diet (0.47 g methionine + 0.26 g cyst(e)ine/100 g diet), thus meeting, but not exceeding, the requirement. Graded levels of choline bitartrate in Experiment 1 and choline chloride in Experiment 2 were added to the basal diet, resulting in eight dietary treatments in each experiment. Dietary treatments were 0, 250, 500, 1000, 2000, 4000, 6000 and 8000 mg choline/kg dry diet. Diets were fed for 12 and 10 wk in Experiments 1 and 2, respectively. Dietary choline concentrations significantly affected weight gain, feed efficiency, survival and total liver lipid concentrations in each experiment. Weight gain and feed efficiency were greatest in fish fed 500 mg choline/kg dry diet as choline bitartrate. Total liver lipid concentrations were variable but tended to be lowest in fish fed diets containing at least 2000 mg choline/kg diet. Survival was significantly lower in the group of fish fed 8000 mg choline/kg diet supplied by choline bitartrate. Weight gain and feed efficiency were greatest and total liver lipid concentration was lowest in groups of fish fed at least 500 mg choline/kg diet as choline chloride; survival was unaffected by dietary treatment. Therefore, choline chloride seems to be a better source of dietary choline than choline bitartrate and 500 mg choline/kg diet is adequate for maximum weight gain and prevention of increased liver lipid concentration in juvenile hybrid striped bass.

Two experiments were conducted to determine the dietary lysine requirement of juvenile hybrid striped bass (Morone saxatilis x M. chrysops). In both experiments the diets contained 35 g crude protein/100 g diet (10 g crude protein supplied by casein and gelatin and 25 g crude protein supplied by crystalline L-amino acids) and contained graded levels of L-lysine.HCl resulting in eight dietary treatments. Diets were fed to triplicate groups of fish and ranged in dietary lysine concentration from 1.2 to 2.6 g/100 g of the dry diet in Experiment 1 and from 0.8 to 2.2 g/100 g of the dry diet in Experiment 2. Weight gain and food efficiency data from Experiment 1 indicated the dietary lysine requirement to be between 1.2 and 1.4 g/100 g of the dry diet. Weight gain, food efficiency and serum lysine data from Experiment 2 confirmed the requirement to be between 1.2 and 1.4 g/100 g of the dry diet. Broken-line analysis of weight gain and food efficiency data from Experiment 2 indicated the dietary lysine requirement to be 1.4 +/- 0.2% of the dry diet, or 4.0 g/100 g of the dietary protein. Changes in the relative proportions of dietary lipid and carbohydrate between the two experiments, although maintaining similar gross energy levels, did not alter the lysine requirement estimate of juvenile hybrid striped bass.

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Two experiments were conducted to determine the dietary arginine requirement of juvenile hybrid striped bass (Morone saxatilis x M. chrysops); a third experiment evaluated the interaction of lysine and arginine. Diets in Experiments 1 and 2 were supplemented with graded concentrations of L-arginine-HCl, resulting in eight dietary treatments. Dietary arginine concentrations ranged from 1.0 to 2.4 g/100 g diet in Experiment 1 and from 0.6 to 2.0 g/100 g diet in Experiment 2. Weight gain was not affected by dietary treatments in Experiment 1. Feed efficiency was significantly affected by dietary arginine concentrations, and the data, when subjected to broken-line analysis, resulted in a requirement estimate of 1.53 +/- 0.20 g/100 g diet. Weight gain and feed efficiency were both significantly affected by dietary arginine concentrations in Experiment 2. Broken-line analyses of weight gain and feed efficiency data indicated the dietary arginine requirement to be 1.55 +/- 0.10 and 1.45 +/- 0.12 g/100 g diet, respectively. Diets in Experiment 3 contained lysine and arginine in ratios of 1:1, 1:1.5, 1:2 and 1:2.5 for the previously estimated requirements for both lysine:arginine and arginine:lysine. No differences were observed in weight gain or feed efficiency for fish fed various lysine:arginine ratios, but serum lysine was significantly different among treatment groups.

KEY WORDS KEY WORDS: essential amino acid requirements, energy : protein ratio, lysine, hybrid striped bass