Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 4, 2005
Publication Date: March 1, 2006
Citation: Lim, C.E., Aksoy, M., Klesius, P.H. 2006. Gossypol in aquaculture diets. Aquafeed Technical Workshop. VICTAM ASIA 2006. Bangkok, Thailand. Technical Abstract: Cottonseed meal ranks third in the word, after soybean meal and rapeseed/canola meal, in term of tonnage produced. Its cost on a per unit protein basis is lower than those of soybean meal and rapeseed/canola meal. Thus, replacement of more expensive protein ingredients by cottonseed meal would reduce feed cost. The amount of cottonseed meal that can be incorporated in aquaculture diets, however, is limited due to the presence of free gossypol, a naturally occurring polyphenolic pigment in the cotton plant. During processing of cottonseed into meal, some free gossypol is bound to lysine, rendering it unavailable to fish. Moreover, the presence of high levels of free gossypol in the diets causes adverse physiological effects on fish. However, the susceptibility of fish to gossypol varies widely among species and parameters evaluated. The growth of rainbow trout was not affected at a dietary free gossypol level of 290 mg/kg but histological changes in livers and kidneys were observed at 95 mg/kg. Tilapia can tolerate relatively high levels of dietary free gossypol. Gossypol from gossypol acetic acid at levels of 1600 and 1800 mg/kg had no adverse effect on the growth of Nile and blue tilapia, respectively. Levels of free gossypol affecting the growth of channel catfish range from 300 to 900 mg/kg. Free gossypol supplemented to practical diets is less toxic to channel catfish than that supplemented to purified diets. Gossypol accumulation in livers is linearly related to dietary gossypol levels. However, catfish fed diets containing natural free gossypol from glanded cottonseed meal accumulate higher levels than those fed diets containing gossypol from gossypol-acetic acid . Regardless of the source of gossypol, the (+)-gossypol isomer is predominantly retained in livers than the (-)- isomer. Because of its anti-microbial and anti-parasitic activities, free gossypol present in cottonseed meal has been suggested as the compound responsible for improving the resistance of channel catfish to Edwardsiella ictaluri infection. Recent studies at our laboratory, however, suggested that this compound may be of little benefit in improving the resistance of catfish against E. ictaluri because the levels found to improve some immune parameters and post-change survival were much higher than those reported to be toxic to catfish. An In vitro study shows that gossypol-acetic acid and (+)- and (-)- optical isomers have antibacterial effect against E. ictaluri but the action is bacteriostatic rather than bactericidal. Thus, compounds in cottonseed meal other that gossypol are responsible for enhancing the resistance of catfish to bacterial infection. Studies to identify these compounds and determine the mechanisms in which these compounds affect immune response and disease resistance in fish are needed.