Nutrient requirements of walleyes (Stizostedion vitreum vitreum)
The protein requirement was determined for 8-g. walleye by feeding one of six isocaloric diets that ranged from 37 to 57% protein and for 50-g. walleye by feeding one of six isocaloric diets that ranged from 32 to 52% protein. Weight gain increased quadratically with increasing dietary protein to a breakpoint of 50% protein for the 8-g. fish and 42% for the 50-g. fish. Carcass fat decreased as dietary protein increased. Percent carcass protein was not affected by dietary protein. The g. of carcass protein gained increased linearly and carcass fat gain increased quadratically as dietary protein increased. Maximum fat gain was predicted to occur at 48% protein for the 8-g. fish and 42% protein for the 50-g. fish. The effects of levels of dietary energy and protein on 16-g. average walleyes were determined in experiment 2. A factorial treatment arrangement was used providing three levels of dietary metabolizable energy (3310, 3530 and 3750 kcal Me/kg) and four levels of protein (37, 44, 51 and 58%). Maximum weight gain occurred with the 51% protein, 3530 kcal Me/kg diet. The percent carcass fat decreased with increasing dietary protein but increased with increasing dietary energy. Carcass protein (%) increased with increasing dietary protein, but was not affected by dietary energy levels. The muscle RNA/DNA ratio increased with increments of dietary protein, but was not affected by dietary Oil, Gas, and Energy;The final experiment compared performance of walleye fed one of two commercial diets (W16, Abernathy) or one of three experimental diets. The ISU-50 diet contained the protein and energy levels that maximized growth in earlier experiments (50% protein, 3500 kcal ME/kg diet) and was supplemented with amino acids to simulate the amino acid profile of the unfertilized walleye egg. An isonitrogenous, isocaloric diet (Exp-50) was formulated using the same ingredients as ISU-50 except that synthetic amino acids were not used, producing a diet with the amino acid profile of anchovy meal and wheat midds. A third experimental diet (Exp-60) was formulated on the basis of amino acid minimums, using anchovy meal as the amino acid source. Weight gain and length gain were greater for the fish fed the ISU-50 diet than for the fish fed the EXP-50 diet, Exp-60 diet or W16. The percentage of carcass fat was lower for the fish fed ISU-50 compared with the fish fed the W16 or Abernathy diets. The percentage of carcass protein was not affected by diet.