Determination of digestibility coefficients of various feedstuffs for red drum (Sciaenops ocellatus)

The availability of nutrients and energy in feedstuffs to fish may vary considerably, depending on a variety of factors including fish species, ingredient quality and processing conditions. The red drum is an emerging aquaculture species for which information concerning nutrient and energy availability is needed to more precisely formulate diets to meet their requirements and to enable effective substitution of ingredients. This study was conducted with red drum to determine apparent organic matter, protein, lipid, and gross energy digestibility coefficients and apparent phosphorus availability of the following ingredients: select (low temperature) menhaden fish meal; regular-quality menhaden Ash meal, poultry by-product meal, meat and bone meal, dehulled soybean meal, cottonseed meal, and wheat. Test diets consisting of a 70:30 mixture of reference diet to test ingredient were utilized with chromic oxide as the non-digestible marker. Organic matter digestibility of ingredients generally decreased as the nitrogen-free extract fraction increased, ranging between 94% for select menhaden fish meal to 47% for wheat. Crude protein digestibility was high for most ingredients, ranging from 77% for regular menhaden fish meal to 97% for wheat, with the exception of poultry by-product meal which was 49%. Lipid digestibility coefficients ranged from 59% for poultry by-product meal to 88% for wheat. Digestible energy coefficients were generally high for the animal meals, ranging from 72% For poultry by-product meal to 95% for select menhaden fish meal however, digestible energy coefficients for plant feedstuffs were considerably lower, from 62% for wheat to 70% for cottonseed meal. Phosphorus availability from animal products was variable, with a low of 27% for poultry by-product meal and a high of 66% for meat and bone meal. Phosphorus availability from soybean meal and cottonseed meal was 47% and 40%, respectively. Wheat had the highest phosphorus availability at 79%. Data from this study indicate red drum can digest and absorb the nutrients in animal products more completely than those from plant products. This difference presumably reflects their inability to effectively digest the nitrogen-free extract portion of plant products. These data provide more precise information concerning nutrient and energy utilization of red drum and will allow ingredient substitutions in practical diet formulations based on levels of available nutrients.