COMPARISON OF CRYSTALLINE LYSINE AND INTACT LYSINE USED AS A SUPPLEMENT IN PRACTICAL DIETS OF NILE TILAPIA (Oreochromis niloticus)

                                                                                                                                                                                                                                    Two feeding trials were conducted using juvenile Nile tilapia, Oreochromis niloticus, to compare the efficiency of crystalline versus intact lysine in practical diets. A high lysine corn protein concentrate (Lysto^TM, Cargill) was used as the intact lysine source. The basal and test diets used in both experiments were designed to be isonitrogenous and isoenergetic containing 32% protein and 8% lipid using primarily plant based protein sources. In the first growth trial, nine dietary treatments ranging in lysine levels from 1.15% (Basal diet) to 1.88% lysine were offered to juvenile fish (6.41 g mean weight). The results obtained after ten weeks indicated that tilapia have positive performance with increasing lysine supplement from both crystalline and intact lysine source. A second series of diets with a broader range of inclusions level of lysine (0.92% to 2.02% diet) were formulated to confirm the results obtained in the first experiment. 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. Juvenile Nile tilapia (6.40 g mean weight) in triplicate aquaria were randomly assigned to each of the experimental diets and fed for eight weeks. The dose-response to increasing dietary lysine levels was particularly clear in the second experiment. Broken-line regression analysis using thermal growth coefficient as a growth rate metric indicated that the lysine requirement of juvenile Nile tilapia was 1.49% while the estimate using quadratic broken-line analysis was slightly lower at 1.45%. The analysis of covariance was conducted on all diets excluded diet 6, 10, 11, which were excess of lysine requirement for tilapia. This analysis indicated there was no significant effect of the type of supplement indicating both are viable options. Overall, the study finding supports the view of prior studies conducted using white leg shrimp and channel catfish that high lysine corn protein concentrate can be used effectively to improve growth performance of tilapia to a level comparable to that obtained from crystalline lysine supplemented diet.