METHIONINE NUTRITION OF TILAPIA

Several dose-response studies were conducted by researchers to determine Methionine (Met) or Methionine + Cystine (M+C) requirement of tilapia including a requirement study with red hybrid tilapia (O. niloticus x O. mossambicus) conducted at Thaksin University, Thailand. It was found that tilapia with an initial body weight (IBW) of 1.7 g/fish required a dietary level of 0.95% and 1.11% Met to obtain optimal SGR and FCR, respectively. This dose-response study used graded levels of supplemental DL-Methionine (DL-Met) or MetAMINO^® and similar to many other studies this study assumed that supplemental DL-Met is utilized by the fish with the same efficiency as Met being released from intact proteins during digestion. This paper explains whether the assumption is true or not.

A trial was conducted with red hybrid tilapia (an average IBW 1.69 g/fish) by Dr. Kiriratnikom and colleagues at Thaksin University, Thailand. The diets and the feeding rates are illustrated in Table 1 & 2 below. Growth performances revealed that feeding rates had strong impact on growth while DL-Met supplementation did not. For example, average SGRs increased from below 1%/d at lowest feeding rate to above 4%/d at highest feeding rate. When SGRs are plotted against dry matter (DM) intake per tank growth responses are found of non-linear curve whereas when crude protein retentions are plotted against DM intake per tank responses turn to be linear. By taken into account both SGR and crude protein responses it indicates that fat more than protein deposition influenced the shape of the growth curve. Is SGR an appropriate response criteria for assessment of the diet quality, in particular dietary protein? Protein retention efficiency was increased from 8 - 9% to 45 - 52% by increasing feeding rate this seems to be in line with general statements that only about 45 - 50% of the protein intake is retained in body protein. It was also found that by inclusion of 0.10% DL-Met protein gain as well as protein and lysine utilization was significantly improved. The slope ratio analysis for Met retention efficiency revealed that the slopes were identical (efficiency 104%, confidence interval 99 - 109) and thus it can be concluded that Met in the supplemented treatment which consisted of 0.55% protein bound Met and 0.10% DL-Met was as efficiently utilized for retention as Met of the basal diet, which consisted only of protein bound Met.