Effect of natural free gossypol and gossypol-acetic acid on growth performance and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge

Abstract

A study was conducted to evaluate the effect of free gossypol from glanded-cottonseed meal (G-CSM) (natural free gossypol) or gossypol-acetic acid on growth performance, body composition, haematology, immune response and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge. Soya bean meal-based diets supplemented with 0, 100, 200, 400, and 800 mg kg−1 free gossypol from G-CSM or gossypol-acetic acid were fed to juvenile channel catfish in triplicate aquaria to apparent satiation twice daily for 12 weeks. Neither sources nor levels of dietary gossypol significantly influenced the final weight gain, feed intake, feed efficiency and survival of channel catfish. Similarly, whole-body proximate composition, haematological parameters (red blood cell, white blood cell counts, haemoglobin and haematocrit), serum protein concentration, macrophage chemotaxis ratio, phagocytic activity and antibody production against E. ictaluri 21-day postinfection were not significantly affected at either dietary sources or levels of gossypol. Gossypol concentrations of liver were linearly related to dietary level of gossypol but the retention rate varied dependent on sources of the dietary gossypol. At dietary gossypol levels of 400 or 800 mg kg−1, total gossypol concentrations in liver of fish fed dietary gossypol from G-CSM were significantly higher than those of fish fed the corresponding levels of gossypol from gossypol-acetic acid. The (+)-isomer of gossypol was predominantly retained in liver regardless of dietary sources of gossypol. The ratio of (+) to (−) gossypol isomers in liver decreased with increasing dietary concentrations of gossypol. Serum lysozyme activity of fish fed dietary gossypol levels of 200 mg kg−1 or higher, either from G-CSM or gossypol-acetic acid, was significantly higher than that of the control. At a level of 800 mg kg−1 diet, gossypol from G-CSM stimulated significantly higher lysozyme activity than gossypol from gossypol-acetic acid. Fish fed diets containing 400 mg kg−1 gossypol or higher from G-CSM or 800 mg kg−1 gossypol from gossypol-acetic acid had significantly increased superoxide anion (O) production. However, neither the sources nor the levels of dietary free gossypol influenced the resistance of juvenile channel catfish to E. ictaluri challenge.