Efeito da salinidade na maturação sexual e no desempenho de Molinésia Velífera

Abstract

Poecilia velifera, commonly called Yucatan molly, is a fish of great interest for ornamental aquaculture. It originates from the Yucatan Peninsula in Mexico, where it can be found in areas with variable salinities. In studies with other species of fish it is observed that salinity interferes with growth, consumption, nutrient utilization capacity and reproductive variables. The objective of the present work was to evaluate the tolerance and the performance of this species in different salinities. In the first experiment, 120 juveniles with 7 days of age were used. These juveniles were abruptly transferred to the salinities of 0, 24, 48, 60, 72 and 78g L-1and held for 96 h, for the median lethal salinity (LS50) estimation. In the second experiment, 160 juveniles, 15-day-old, were gradually acclimated to the tested concentrations of 0, 12, 24 and 36g L-1. In this experiment, the performance was evaluated for a period of 75 days. In the next step, the fish were kept for another 75 days to observe the weight and length of the males at the moment of the copulatory organ formation and a proportion of males and females in each treatment. Using the same fish from experiment two, being maintained in the respective treatments, a reproduction phase was initiated with 8 females and 4 males of each salinity, totalizing 32 females and 16 males. Thisstage had a period of 65 days, of which 15 days the females were in contact with the male. In experiment 1, a LS50-24h was estimated at 72g L-1, while at 48 and 72h, both were estimated at 71.6g L-1. The LS50-96h was estimated at 71.1g L-1. In Experiment 2, juveniles were exposed to different salinities and survival was 100% in all treatments. The final weight, weight gain and food intake were inversely proportional to the increase in salinity. The final length showed a linear response with constant valuesfor estimated salinity of 23.4g L-1and reduction in the highest salinities. The apparent feed conversion rate was directly related to the increase in salinity. In freshwater,the early onset of secondary sexual characteristics was recorded. The saline concentration of the medium had a negative correlation with the size and length of the male,when the anal fin was altered in a copulatory organ. The salinity also affected a sexual proportion. In both treatments with higher saline concentration, 24 and36g L-1occurred predominance of females. The mollies kept in freshwater environment were more precocious in relation to the other treatments, since 50% of the females of this treatment reproduced, whereas this did not occur for any fish of the other treatments tested. The study showed that P. velifera is a euryhalinespecies, but they presented better performance under freshwater conditions.