Submitted to: Global Aquaculture Advocate
Publication Type: Popular publication
Publication Acceptance Date: 12/17/2002
Publication Date: 12/31/2002
Citation: Lim, C.E., Yildirim, M., Klesius, P.H. 2002. Effect of substitution of cottonseed meal for soybean meal on growth, hematology and immune responses of tilapia (Oreochromis niloticus). Global Aquaculture Advocate. 5(6):28-30. Interpretive Summary: Soybean meal (SBM) is currently comprised up to 50% of the diet of tilapia. Replacement of SBM with less expensive plant protein would be beneficial in reducing feed costs. Cottonseed meal (CSM), which ranks second in the United States in terms of tonnage produced, is less expensive than SBM on a per unit protein basis. Earlier studies have shown that the amount of CSM that can be included in fish diets depends mainly on the species, and levels of free gossypol and available lysine. No information is available on the influence of dietary CSM on fish immunity. Thus, this study was conducted to evaluate the effect of replacement of different levels of CSM for SBM on growth performance, hematology and immune responses of Nile tilapia. Results show that feed intake, survival, total cell count, red blood cell count, and serum protein and activity of an enzyme that can breakdown the bacterial cell walls were not affected by dietary levels of CSM. Based on weight gain (WG) and feed efficiency ratio (FER), however, only one-third of SBM in tilapia diet can be replaced by 19% CSM. Increasing dietary CSM levels to 38% or higher adversely affected WG, FER, percent packed cell volume and hemoglobin but increased the production an oxygen radicals that are harmful to bacteria and percent of macrophage engulfing two or more bacteria. Studies to identify compounds in CSM responsible for improvement of tilapia immune responses and their influence on disease resistance are warranted.
Technical Abstract: Four isoproteinic (32% protein), isocaloric (2,900 kcal/kg) diets were formulated to contain 0, 19, 38 and 57% CSM as substitutes on an equal nitrogen basis for 0, 33.3, 66.7 and 100% of SBM. Each diet was fed to juvenile tilapia (5.7 g average weight) in four replicate aquaria to apparent satiation twice daily for 12 weeks. Dry matter feed consumption and survival were not affected by dietary levels of CSM but weight gain (WG) and feed efficiency ratio (FER) were adversely affected as the dietary CSM levels increased to 38%or higher. No significant differences were observed among the GD and FER of fish fed diets containing 19 to 57%. Total cell count (TCC) and red blood cell count (RBC) were not significantly affected by increasing levels of dietary CSM. Hematocrit (Ht) and hemoglobin (Hb) were similar for fish fed diets without or with 19% CSM but significantly decreased when CSM levels were increased to 38% or higher. Serum protein concentration and lysozyme activity were not affected by dietary levels of CSM. Superoxide anion production measured by nitroblue tetrazolium assay significantly increased for fish fed the highest (57%) CSM diet. Phagocytic activity of macrophage of fish fed the 38% CSM diet was significantly higher than that of the control but did not differ from those of the other treatments. Results of this study indicate that one-third of SBM in tilapia diet can be replaced by 19% CSM without affecting the growth performance, hematocrit and hemoglobin. Increasing CSM level to 38% or higher increased superoxide anion production and phagocytic activity of macrophage. Dietary levels of CSM, however, had no effect on feed intake, TCC, RBC, and serum protein and lysozyme activity.