Efeito da suplementação de diferentes níveis de vitamina C na reprodução e qualidade de ovos e larvas de Tilápia do Nilo

Abstract

The objective of this study was to evaluate the effect of vitamin C on the performance, reproductive parameters and quality of eggs and larvae of the Nile tilapia (Oreochromis niloticus) kept in a water recirculation system. Four isonitrogenous and isoenergetic diets with different levels of vitamin C (0, 261, 599 and 942 mg/kg of food) were tested for males and females. Males were extruded for four consecutive weeks. For females, the same levels of Vitamin C were used. After 45 days, reproduction was carried out for four weeks. In order to assess the quality of the larvae, 40 and 50 minute air exposure as well as larvae incubation tests were performed during the lecithotrophic period at different salinity levels (from 0 to 6 g salt /L). Sperm variables, motility, vigour and sperm concentration were higher in fish fed diets containing 599 and 942 mg vitamin C/kg. The gonadosomatic index, semen volume performed on the fourth collection and plasma protein showed direct relationship with the increase of vitamin C levels in the diet. No changes were observed in the heptosomatic index and blood glucose. The hematocrit and erythrocyte showed better values estimated by the equations derivative at 850 and 638 mg vitamin C/kg of food, respectively. The leukocytes presented an inversely proportional relation to the increase of vitamin C levels in the food. Flagellar beating showed better results for breeders fed with diets containing 942 and 599 mg vitamin C/kg of food. For the variables: linearity, actual trajectory speed, linear trajectory speed, and sperm average trajectory speed, higher values were observed with the highest level of vitamin C in the diet. For females, the highest gonadosomatic indexes, egg weight and hatching larvae measures were recorded in fish fed with diets containing 599 and 942 mg vitamin C/kg of food. Hepatosomatic index, total and relative fecundity were higher for females that received 599 mg of vitamin C/kg of food. Regarding the largest diameter and smallest diameter of the eggs, and the measures of larvae 120 hours after hatching, the lowest values were observed for those from females fed without vitamin C. The hatching rate, average egg production per female and average production of larvae per female showed direct relationship with the increase of vitamin C levels on the diet. The hematocrit, leukocytes, erythrocytes and total plasma protein were worse in females that did not receive vitamin C in the diet. Glucose, after the reproductive period, was lower for the 942 mg vitamin C/kg diet treatment, and higher with no vitamin C in the diet. When the eggs were incubated in different salinity levels, the worst survival rate was for the treatment with no vitamin C at the end of 120 hours of incubation. For the 40 and 50-minute exposure to air test, resistance to stress of newly hatched larvae was higher for larvae from females who received 942 mg vitamin C/kg of food, intermediate for the 599 mg vitamin C/kg food and lower for other treatments. In conclusion, the addition of 599 and 942 mg of vitamin C optimised the reproductive parameters, blood variables of breeders and quality of eggs and larvae of Nile tilapia.