Long-term effects of dietary cottonseed meal on growth and reproductive performance of rainbow trout: Three-year study

A long-term feeding experiment (35 months) was conducted to study the effects of substitution of fish meal (FM) by cottonseed meal (CM) on growth, feed utilization and reproductive physiology in rainbow trout (Oncorhynchus mykiss). Five groups of fish (1.5 years old; 246 ± 10 g) were fed one of five experimental diets formulated to substitute FM with CM (147, 294, 441 and 588 g/kg designated as diets CM0, CM25, CM50, CM75 and CM100, respectively, based on percentage of protein replacement). The results showed that dietary CM significantly affected the coefficient of total apparent digestibility (CTTAD) of protein and phosphorus. However, in the long-term, it did not impact fish growth. Growth rates within male and female groups were not significantly affected by the dietary CM replacement after the 3 years of feeding. Gossypol-related mortality was not found in the fish during the 3 years of feeding. Muscle gossypol concentrations after 3 years were significantly different among groups and corresponded to the dietary concentration. Less than 1.0 μg gossypol/g wet basis of muscle was found in the highest dietary CM group. In males, the concentration of steroid hormones and the reproductive performances including sperm concentration, motility and eyed-stage embryo survival in the third year of this study were not significantly affected by the dietary CM inclusion. In contrast, female rainbow trout fertility and plasma testosterone levels were negatively affected by complete replacement of FM protein with CM protein. The findings based on this long-term study suggest that high dietary CM supplementation up to 58.8/100 g or complete substitution of FM protein does not impair growth of both sexes and reproductive performance of male rainbow trout, and that humans can safely consume the fillet produced by fish fed CM-containing diets.