Avaliações de efeitos decorrentes de alterações energéticas da dieta em tilápia do Nilo (Oreochromis niloticus) em período reprodutivo

Abstract

This study evaluated the effects of digestible energy levels for hematology parameters, liver histology and leptin concentrations in visceral fat, liver, ovary and plasma in female Nile tilapia (Oreochromis niloticus), UFLA strain in its first reproductive cicle. A total of 60 Nile tilapia broodstock; 45 females and 15 males with an average weight of 79.17 ± 15.12 g and 82.6 ± 10.98 g, respectively, were used in a completely randomized design with five treatments and three replications, being four fishes by repetition. Fish were selected, identified with microchips and distributed in tanks in the ratio of one male to three females. The fish were fed for 60 days with isoproteic diets (38%) containing five digestible energy levels (3,200; 3,400; 3,600; 3,800 and 4,000 kcal/kg diet). The blood was collected by puncture of the tail vein with syringe containing EDTA and used for blood smears, hematocrit, total count of red blood cells, thrombocytes and leukocytes, differential leukocyte count, determination of glucose and total plasma protein. Quantification of leptin in the plasma and tissues was performed by colorimetric ELISA kit. Conventional histological analysis by hematoxylin and eosin (HE), evaluation of triglycerides with the color of Sudan III and glycogen with periodic acid-Schiff (PAS) were performed in liver tissue. No significant difference was observed (p>0.05) in hematological values, glucose and total protein in plasma, however, thrombocytopenia was observed in all experimental fish. Leptin concentrations found in the visceral fat in fishes fed with diet 3,200 kcal/kg were higher compared to the other experimental diets (p<0.05). There were no differences (p>0.05) in leptin concentrations (ng/ml) in ovarian and liver. The ELISA technique used not detected leptin concentrations in plasma. The most severe microscopic lesions in the hepatic parenchyma, cytoplasmic vacuolation, inflammatory cell infiltration, necrosis, and congestion of blood vessels, the highest rates of lipid inclusions in hepatic parenchymal (p<0.05) and larger diameters (um) of lipid droplets (p<0.05) in liver were observed in the fish fed diets with 3,600; 3,800 and 4,000 kcal/kg. Therefore, it is suggested that the digestible energy level of 3,400 kcal/kg in diet for Nile tilapia female in reproductive period.