Estudo de tolerância dos juvenis de tilápias - Oreochromis mossambicus à diferentes níveis de salinidades da água

Abstract

The brackish waters are an alternative for the expansion of aquaculture, favoring the cultivation of salinity-tolerant tilapia. In addition to the particularities of each species, factors such as the adaptation strategy, the age of the fish at the moment of transfer and the previous exposure of eggs and post-larvae to the water of higher salinity seem to affect the tolerance of the tilapia to the salinity. The present study was carried out at the School of Marine and Coastal Sciences with the objective of tolerating the juveniles of Oreochromis mossambicus subjected to variations in salinity. The experimental design consisted of five triplicate treatments at each salinity (0, 15, 25, 35 and 45 ‰). The individuals were populated in PVC plastic buckets with a volume of 20 liters each with 5 juveniles per treatment for 96 hours, without any aeration. The mean weight presented was 21.8 ± 9.5g and 21.2 ± 7.1g, with a density of 54 m2. The water quality parameters (temperature, oxygen, and pH) were monitored hourly. The results showed that all monitored water quality parameters were within the normal levels of tilapia cultivation specifically during their juvenile phase, but higher survival rates were observed in juveniles submitted to salinities of 15% o (60% of them survived), and lower survival rates in juveniles subjected to 25% o and 35% o (20% of fish survived). Statistical analyzes according to the Chi-square statistical test (with a significance level of 0.5), it was observed that the values of percentages of survival rate did not follow the distribution observed in this study Chi-square (calc.) = 49.3; against the Chi-square (table) = 5.2. However, it was also highlighted that the parameters of water quality (physical and chemical) monitored were within the normal levels, and there may be variations in the replicates of the different salinity. Another limiting factor in the cultivation is ammonia, nitrite and nitrate, which were not monitored in this study, and may have some influence on survival rates at different salinities.