Levels of dietary gossypol affect growth and bacterial resistance of Nile tilapia

Authors: Lim, Chhorn; Aksoy, Mediha; Klesius, Phillip

Submitted to: Global Aquaculture Advocate
Publication Type: Popular Publication
Publication Acceptance Date: 1/15/2003
Publication Date: 3/24/2003
Citation: Lim, C.E., Aksoy, M., Klesius, P.H. 2003. Levels of dietary gossypol affect growth and bacterial resistance of Nile tilapia. Global Aquaculture Advocate. 6(5):42-43.

Interpretive Summary: Gossypol, a naturally occurring polyphenolic pigment in cottonseed, is toxic to fish when presence in large amount. No information is available on the toxicity of gossypol in Nile tilapia. Thus, this study was conducted to evaluate the effect of graded levels of gossypol from gossypol-acetic acid on growth performance, hematology, immune response and resistance to Streptococcus iniae of Nile tilapia fed purified diets containing 0, 50, 100, 200, 400, 800 and 1600 mg/kg diet of gossypol from gossypol-acetic acid. Weight gain significantly increased at each incremental level of dietary gossypol up to 100 mg/kg. No differences were observed among weight gain of fish fed diets containing 100 mg or higher gossypol diets. Feed efficiency values were a reflection of weight gain. Survival was not affected by dietary levels of gossypol. Red blood cell count significantly increased for fish fed 800 but did not differ for fish fed other diets. White blood cell count, hematocrit, hemoglobin and serum protein did not differ among treatments. Serum lysozyme activity of fish fed the 200-mg gossypol diet was significantly higher than those of fish fed the control and 50-mg gossypol diets but did not differ from those of fish fed diets containing 100 mg/kg or higher gossypol. Antibody titer at day 15 post- challenge did not differ among treatments. Cumulative mortality 14 days post challenge with S. iniae was significantly lowest for fish fed the 100-mg gossypol diet. Highest mortality was obtained with fish fed the 800-mg gossypol diet but this was not significantly different from those of fish fed 0, 50, 200 and 1,600-mg gossypol diets. This study indicates that, compared to trout and channel catfish, juvenile Nile tilapia can tolerate very high levels of dietary gossypol. A dietary gossypol level of 100 mg/kg was beneficial in improving growth, feed efficiency and the resistance of Nile tilapia to S. iniae infection.

Technical Abstract: A study was conducted to evaluate the effect of dietary levels of gossypol from gossypol acetic acid on growth, hematology, immune response and resistance of Nile tilapia to Streptococcus iniae. A purified basal diet supplemented with 0, 50, 100, 200, 400, 800 or 1,600 mg/kg diet of gossypol from gossypol-acetic acid was fed to juvenile tilapia (4.4 ± 0.1 g) in triplicate aquaria to satiation twice daily for 12 weeks. Final weight gain significantly increased at each incremental level of dietary gossypol up to 100-mg/kg. No differences were observed among weight gain of fish fed diets containing 100 mg or higher gossypol diets. Feed efficiency values were a reflection of weight gain. Survival was not affected by dietary levels of gossypol. Red blood cell count significantly increased for fish fed the 800-mg gossypol diet but did not differ for fish fed other diets. White blood cell count, hematocrit, hemoglobin and serum protein did not differ among treatments. Serum lysozyme activity of fish fed the 200-mg gossypol diet was significantly higher than those of fish fed the control and 50-mg gossypol diets but did not differ from those of fish fed diets containing 100 mg/kg or higher gossypol. Antibody titer at day 15 post- challenge did not differ among treatments. Cumulative mortality 14 days post challenge with S. iniae was significantly lowest for fish fed the 100-mg gossypol diet. Highest mortality was obtained with fish fed the 800-mg gossypol diet but this was not significantly different from those of fish fed 0, 50, 200 and 1,600-mg gossypol diets. This study indicates that juvenile Nile tilapia can tolerate high levels of dietary gossypol. A dietary gossypol level of 100 mg/kg was sufficient to improve growth, feed efficiency and the resistance of Nile tilapia to S. iniae infection.