Comparison of crystalline lysine and intact lysine used as a supplement in practical diets of channel catfish (Ictalurus punctatus) and Nile tilapia (Oreochromis niloticus)

The study was conducted using channel catfish and tilapia to evaluate the production performance of these fish to increasing levels of lysine from crystalline and intact lysine supplemented in practical diets. A practical lysine deficient basal diet was developed using corn protein concentrate (Empyreal® 75) as a primary protein source. To this diet either graded levels of crystalline lysine or similar levels from a high lysine corn protein concentrate (Lysto™) were added. In the channel catfish trial, the first five diets were designed to contain increasing levels of crystalline lysine (1.21%, 1.34%, 1.45%, 1.56%, and 1.72%) with an additional four diets using intact protein from a high lysine corn protein concentrate (1.40%, 1.57%, 1.77%, and 1.91% lysine). In the tilapia trial, lysine from two sources was added to 11 diets to produce analyzed lysine levels of 0.92%, 1.11%, 1.23%, 1.34%, 1.54% 1.65% in the first six diets using crystalline lysine and 1.13%, 1.38%, 1.61%, 1.81%, 2.02% in the last five diets using intact lysine. Results indicated that channel catfish and tilapia have positive performance with increasing lysine supplementation up to the requirement. Fish fed with the higher levels of lysine had the highest weight gain and lowest feed conversion ratio. The regression analysis on the increased level of inclusion of crystalline lysine and intact lysine showed no significant difference in slope. Based on the growth, feed conversion ratio and apparent net protein retention data obtained from this study, it can be concluded that the effectiveness of using intact lysine via high lysine corn protein concentrate as a lysine supplement is not significantly different from crystalline lysine. Thus, the high lysine corn protein concentrate is a feasible ingredient for aquaculture feeds, which can be used to balance the amino acid composition of the diet without addition of crystalline lysine.