Impact of different levels of dietary myo-inositol on the growth performance, histological structure of gonads and liver of red tilapia reared in brackish water

Abstract

A 120 day growth trial was conducted to evaluate the dietary inositol using diets (25.7% crude protein pelleted diet). These diets were formulated to contain graded levels of supplemental myo-inositol (MI) (0, 300, 400 and 500 mg/kg). Four conical bottom fiberglass tanks (500 L.) were used and stocked with fifty red tilapia in each tank with initial weight (average weight) of 1.82 g ± 0.03). Fishes were fed twice daily at a rate of 8% of live body weight for 6 days a week. Significantly, the best value of average final body weight was observed at 500 mg/kg inositol (MI) followed by 400 mg/kg diets (p.0.05). Female red tilapia which fed on diets that contained 400 and 500 mg/kg inositol showed many types of atresia, each one had its specific feature such as degeneration of the nucleus, liquification of cytoplasm and yolk. Also, hypertrophy of the follicular cell acted as phagocytic cells which invaded the oocyte from out side. The testis of red tilapia fed diets supplemented with 300 and 400 mg/kg was not affected by dietary treatments and the results revealed normal development of active spermatogenesis process at maturation, nearly ripe and spawning stages, while the testis of fish fed diets supplemented with 500
mg/kg showed resorption of spermatozoa and thick lobules boundary tissue. The liver of fish fed diets that contained 300 mg/kg (MI) revealed that hepatocytes had distracted membrane and faintly stained cytoplasm. Pycnotic nuclei are common. With increased dose of (MI) to 400 mg/kg the pyenotic nuclei and cytoplasmic vacuolation was obtained. With increased dose of (MI) to 500 mg/kg diets, lipid infiltration, lipid metabolic disturbance resulted in the accumulation of lipid in liver, decreased hepatic
lipoprotein output and intestinal lipodystrophy. The recommended dose is 400 mg/kg diets to obtain normal males. Also, the results explained the mechanism of inositol action through reproduction dysfunctions and recruitment failure which occurred at dose more than 400 mg/kg (MI) and the recruitment caused a reduction in population size.