Nutrient digestibility of common feedstuffs in extruded diets for sunshinebass Morone chrysops female x M-saxatilis male

The digestibility of nutrients and energy in various ingredients to fish is affected by a variety of factors including ingredient quality and processi ng. Limited information is available regarding the digestibility of nutrien ts in feedstuffs for sunshine bass Morone chrysops female x M. saxatilis ma le. This information is particularly needed to improve the accuracy of diet formulations and allow appropriate substitution of feedstuffs. Therefore, a study was conducted with advanced sunshine bass fingerlings (50-75 g) to determine the apparent digestibility coefficients (ADCs) for protein, lipid , carbohydrate, gross energy, and organic matter in a variety of feedstuffs in extrusion-processed diets. Included in the study were low-temperature p rocessed menhaden fish meal (Select(TM)), meat and bone meal, fish meal ana log (PROPAK(TM)), dehulled soybean meal, cottonseed meal, corn grain, sorgh um, wheat hour, wheat middlings, and rice bran. Test diets consisted of a 7 0:30 mixture of reference diet to test ingredient with chromic oxide (0.8%) as the inert marker. Reference and test diet ingredients were mixed in a c ommercial ribbon blender, preconditioned and extruded on a Wenger X-20 to p roduce a neutrally buoyant pellet (5 mm). The digestibility trials were con ducted in six 600-L rectangular tanks connected as a closed recirculating b rackish (5-7 ppt) water system. Diets were randomly assigned to tanks of 45 -50 sunshine bass and fed twice daily to satiation. Feedstuffs of high-prot ein and high-lipid content mere better digested by sunshine bass than feeds tuffs of high carbohydrate or high fiber content. Organic matter digestibil ity ranged from 42% for both sorghum and corn to 96% and 98% for meat and b one meal and Select(TM) menhaden fish meal, respectively. Select(TM) menhad en fish meal and meat and bone meal appeared to be the best ingredients for sunshine bass diets in terms of overall nutrient profiles and digestibilit y of nutrients. The fish meal analog did not perform as favorably as the ot her two animal products. Protein and lipid of cottonseed meal were highly a vailable to sunshine bass with ADCs of 85% and 92%, respectively. Protein d igestibility was high for soybean meal (77%), whereas the digestibility of organic matter (51%), lipid (54%), carbohydrate (25%) and energy (56%) in t his feedstuff was moderately low. Energy in wheat middlings and wheat also was moderately available at 67% and 59%, respectively. Energy in sorghum an d corn was much less available at 44% and 40%, respectively. Digestibility of nutrients and energy in rice bran exceeded 90%. Use of this information should aid the development of more efficient and economical diet formulatio ns for sunshine bass.