Effects of the salinity variation on the survival and reproductive success of Xiphophorus maculatus (Cyprinodontiformes: Poeciliidae)

Abstract

Fish are affected by environmental variables that influence their survival and reproduction, showing physiological responses in an attempt to maintain internal homeostasis. Several Poeciliidae, native from brackish water body regions, can be acclimated to live in saltwater. The introduction of Xiphophorus maculatus in saline environments is possible, although it is not a brackish water species. Thus, to evaluate the effects of the salinity variation on the acclimatization of X. maculatus, the specimens were exposed to different salinities (from 15 to 30 ppt) for up to 40 days, acutely and gradually. After exposing, their gonads, gills, cortisol and glucose levels were analysed. When transferred to salt or brackish water, cortisol and glucose levels increased, peaking at 30 min. Immunohistochemistry showed increased expression of Na+/K+‐ATPases in the mitochondria‐rich cells (MRCs) of the gill, as salinity increased. The female and male germinal epithelium remained unchanged. Xiphophorus maculatus was able to acclimatize and reproduce in saltwater, and their offspring survived in this environment, when there was gradual acclimatization of the adults to different salinities. However, in an abrupt exposure, the salinity became a stressor agent and could cause its mortality.