Add time:08/16/2019         Source:sciencedirect.com

This study was conducted to evaluate the effect of gossypol levels on growth performance, body composition, hematology, immune response and resistance of channel catfish to Edwadsiella ictaluri challenge. A purified basal diet supplemented with 0, 300, 600, 900, 1200 and 1500 mg of gossypol from gossypol–acetic acid was fed to juvenile channel catfish in quadruplicate aquaria to apparent satiation twice daily for 12 weeks. Final weight gain was inversely related to the concentration of dietary gossypol. Fish fed diets without and with 1500-mg gossypol/kg had significantly highest and lowest weight gain, respectively. Feed intake and feed efficiency were a reflection of weight gain. Survival was not affected by dietary levels of gossypol. Whole body moisture increased whereas lipid decreased with increasing dietary gossypol concentrations. Body protein significantly decreased in fish fed with 1500-mg gossypol diet, but did not differ among fish fed with other diets. Body ash did not differ in fish fed diets containing 0–900-mg gossypol/kg but was significantly higher in fish fed higher levels of dietary gossypol. Gossypol concentration in liver was linearly related (R2=0.991) to dietary levels of gossypol. Ratio of (+) to (−) gossypol isomers in liver of fish fed with different diets was relatively constant. Red blood cell (RBC) count of fish fed with the two highest levels of dietary gossypol (1200 and 1500 mg) was significantly lower than those of fish fed with control diet. Hemoglobin significantly decreased in fish fed with 900 mg or higher gossypol diets. Hematocrit was significantly affected at each incremental level of dietary gossypol of 600 mg/kg or higher. Serum protein did not differ for fish fed with the three lowest dietary levels of gossypol but was significantly reduced at 900 mg or higher gossypol. Macrophage chemotaxis ratio was similar for groups fed diets containing gossypol but was significantly higher than that of fish fed with the control diet. Serum lysozyme activity significantly increased at dietary gossypol levels of 900 mg or higher. Superoxide anion production as measured by nitroblue tetrazolium (NBT) reduction assay did not differ among treatments. Mortality at 14-day post-challenge with E. ictaluri significantly decreased at dietary gossypol levels of 900 mg or higher. However, antibody titer against E. ictaluri 15-day post-challenge was not affected by dietary treatments. This study indicates that juvenile channel catfish was more sensitive to gossypol toxicity than previously reported. The toxic concentration ranged from 300 to 1200 mg gossypol/kg diet depending on the parameter evaluated. However, improved macrophage chemotaxis ratio, serum lysozyme activity and resistance of catfish to E. ictaluri challenge were observed at dietary levels of 900 mg gossypol/kg or higher.

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