Apparent digestibility of selected ingredients in red drum (Sciaenops ocellatus) diets

Production of cultured red drum requires use of formulated diets for grow-out to marketable size. However, insufficient information is available regarding the nutrition of this species to make least-cost feed formulation practical. Knowledge of the digestibility of ingredients used in red drum diets could facilitate least-cost formulation and reduce feed costs. The objective of this study was to determine apparent digestibility of dry matter, crude protein, and energy in blood meal, corn grain, cottonseed meal, grain sorghum, meat and bone meal, menhaden fish meal, rice bran, soybean meal, and wheat middlings in formulated red drum diets. Digestibility coefficients were determined using a reference diet and test diets that contained 70% of the reference diet mixture and 30% test ingredient. All diets contained 1% chromic oxide as a digestibility indicator. Fecal samples were manually stripped from anesthetized fish to prevent contact with water. Apparent digestibility coefficients for dry matter, crude protein, and energy in the reference and test diets were determined, and digestibility coefficients for the test ingredients were calculated based on differences in the digestibility of test diets relative to the reference diet. Apparent crude protein digestibility coefficients ranged from 74 to 100% for all feedstuffs tested, indicating that red drum utilized dietary protein efficiently regardless of source. Protein digestibility was highest in feedstuffs with high protein content (> 60%) and low fiber content (< 2%). Apparent energy digestibility was relatively low for animal products (54-60%) and lower for plant products (12-52%). Dry matter digestibility varied more among ingredients of plant origin (18-68%) than among those of animal origin (65-77%). Apparent digestibility of dry matter and energy was positively influenced by protein and lipid content of the ingredient and negatively influenced by crude fiber content. Digestibility of starch appeared to vary widely among plant products.