DIETARY ISOLEUCINE REQUIREMENTS OF NILE TILAPIA JUVENILES BASED ON GROWTH PERFORMANCE, AMINO ACIDS RETENTION AND EXPRESSION OF MUSCLE-GROWTH RELATED GENES

Nile tilapia (Oreochromis niloticus) is the main species created in Brazil, due to its rapid growth, good adaptation to the environment and the taste of the meat. Due to advances in genetic breeding and precision nutrition, it is necessary to formulate diets that meet the nutritional requirements of fish, especially regarding the essential and non-essential amino acids, important for protein synthesis and consequent muscle growth of fish. The study was conducted to evaluate the effect of isoleucine on the expression of genes related to muscle growth in juveniles of Nile tilapia.

An eight - week feeding experiment was conducted with 288 Nile tilapia juveniles (mean weight 2.46 g) stored in 24 aquariums with 12 fish each. In each aquarium, an aeration system was maintained to keep the oxygen content between 5 and 6 mg/L. The monitoring of the parameters of temperature, pH, alkalinity, nitrite and nitrate of the water of each aquarium was carried out three times a week. Six diets were prepared with approximately 264.4 g kg^-1 crude protein and 3072.77 Kcal kg^-1, which contained 8.5, 11.0, 13.8, 17.0, 20.5 and 23.4 g kg^-1 L-isoleucine. To verify the muscle growth of the fish, the expression of MyoD and MyoG genes (myogenin) was performed on the white musculature by RT - qPCR.

Fish fed with 13.8 g kg^-1 of isoleucine presented higher final body weight (49.0 g; P<0.001) and weight gain (46.5 g; P=0.002) compared to fish fed with 8.5 g kg^-1 of isoleucine (38.6 g and 36.1 g, respectively). Expression of MyoD mRNA levels was not influenced (P>0.05) by isoleucine levels. The expression of MyoG mRNA was influenced (P <0.05) by the level of 13.8 g kg^-1 of L-isoleucine in relation to the other levels (Fig 1). Juveniles of tilapia fed 13.8 g kg^-1 of L-isoleucine have higher expression of genes related to muscle development (myogenin)