Muscle Growth of Two Nile Tilapia （Oreochromis niloticus） Strains

The objective of this research was to evaluate the muscle growth of the Nile tilapias of Thai and supreme strain. Hyperplasia and hypertrophy of muscle fibers were studied by histology. The fish were cultivated in cages in a dam and as they grew they were weighed and measured in length. In tissue samples, it was evaluated the quantity of cells area~ and the diameter of the white, pink and red muscle fibers. The supreme strain presented greater number of white and pink fibers mm2 and smaller number of red fibers when compared to the Thai strain. 5-10 cm fish presented higher number of white, pink and red fibers mm： and smaller average diameter of the white and pink fibers, when compared to a 10-15 cm fish. The average diameter of the white and pink fibers increased in 10-15 cm fish, compared to 5-10 era. White fibers smaller than 10 ~tm were found only in the 5-10 cm supreme strain. Tilapias of Thai and supreme strain presented different standard distribution of red, pink and white muscle fibers. Supreme strain, genetically improved, presented higher hyperplasia of white fibers than Thai strain, and this can indicate its higher potential growth.