Submitted to: Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/9/2003
Publication Date: 5/10/2003
Citation: Yildirim, M., Lim, C.E., Wan, P., Klesius, P.H. 2003. Growth performance and immune response of channel catfish (Ictalurus punctatus) fed diets containing graded levels of gossypol - acetic acid. Aquaculture. 219:751-768. Interpretive Summary: Gossypol, a naturally occurring polyphenolic pigment in cottonseed, is toxic to fish when presence in large amount. However, previous studies at our laboratory have indicated that gossypol or other compound present in cottonseed meal may have beneficial effect by improving the immune response and resistance of juvenile channel catfish against Edwardsiella ictaluriinfection. Thus, this study was conducted to evaluate the growth performance, hematology, immune response and resistance to E. ictaluri of catfish to fed purified diets containing 0, 300, 600, 900, 1200 and 1500 mg gossypol from gossypol-acetic acid.. Results showed that weight gain, feed intake and feed efficiency were inversely related to dietary levels of gossypol. Gossypol accumulation in liver was linearly related to dietary levels of gossypol. Hematocrit, hemoglobin and red blood cell count significantly decreased at dietary levels of gossypol of 600 mg/kg or higher, 900 mg/kg or higher and 1200 mg/kg or higher, respectively. Serum protein significantly decreased whereas serum lysozyme activity increased at dietary gossypol levels of 900 mg or higher. Number of a phagocytic cell migration in the presence of the bacterial protein was similar for fish fed diets containing gossypol but was significantly higher than those fed diet without gossypol. Gossypol levels had no effect on the production of su-peroxide anion by phagocytic cells. Mortality 14-day post challenge with E. ictaluri significantly decreased at dietary gossypol levels of 900 mg or higher. However, antibody production 15-day post challenge was not affected by dietary gossypol levels. This study shows that the toxic levels of gossypol for catfish is much lower than earlier reported and ranged form 300 to 1200 mg/kg diet depending on the parameter tested. Improved immune response and resistance of fish to E. ictaluri challenge were obtained at dietary gossypol levels of 900 mg/kg or higher. Gossypol is of little benefit in improving the resistance of catfish to E. ictaluri infection unless a concentration lower than that affecting the growth performance is found.
Technical Abstract: A study was conducted to evaluate the effect of dietary gossypol levels on growth, hematology, immune response and resistance of channel catfish to Edwardsiella ictaluri. A purified basal diet supplemented with 0, 300, 600, 900, 1,200 and 1,500 mg gossypol from gossypol-acetic acid were fed to juvenile channel catfish in quadruplicate aquaria to satiation twice daily for 12 weeks. Final weight gain was inversely related to the concentration of dietary gossypol. Fish fed diets without and with 1,500 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 levels. Body protein was significantly low for fish fed the highest gossypol diet, but did not differ among fish fed the other diets. Body ash did not differ in fish fed diets containing 0 to 900 mg gossypol/kg but was significantly higher in fish fed higher levels of gossypol. Liver gossypol content was linearly related to dietary levels of gossypol. Ratio of gossypol isomers (+ and -) in liver of fish fed different diets was relatively constant. Total cell count and red blood cell count of fish fed the two highest levels of dietary gossypol were significantly lower than those of fish fed the control diet. Hemoglobin significantly decreased in fish fed 900-mg or higher gossypol diets. Hematocrit was significantly affected at each incremental level of dietary gossypol of 600 mg/kg or higher. Plasma protein did not differ for fish fed the three lowest dietary levels of gossypol but was significantly reduced at 900 mg or higher gossypol. Macrophage chemotaxis ratio was similar for the groups fed diets containing gossypol but was significantly higher than that of fish fed the control diet. Plasma lysozyme activity significantly increased at dietary gossypol levels of 900 mg or higher. Superoxide anion production as measured by NBT test did not differ among treatments. Mortality 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 treatment. This study indicate that juvenile catfish were more sensitive to gossypol toxicity than previously reported. The toxic concentration ranged from 300 to 900 mg gossypol/kg diet depending on the parameter evaluated. However, improved macrophage chemotaxis ratio, plasma lysozyme activity and resistance of fish to E. ictaluri challenge were observed at dietary levels of gossypol of 900 mg/kg or higher.