The effects of hypersalinity on the physiology and morphology of a livebearing fish

The Poeciliidae family of livebearing fish exhibit broad environmental tolerances and occupy some of the most extreme aquatic environments on earth. One group in particular, the Limia genus, is widespread throughout freshwater habitats in the Dominican Republic and has also colonized hypersaline lagoons at salinity levels more than twice that of sea water. Populations found in hypersaline conditions appear to be smaller and less colorful than their freshwater counterparts. We hypothesize that these changes to morphology may be related to the energetic cost of osmoregulation in an extremely hypertonic environment. Here we use geometric morphometrics to quantify morphological differences, including size and shape, of freshwater and hypersaline populations of L. perugiae. We correlate changes to size and shape with an increase in energy usage by the active ion transport mechanisms of the mitochondria rich cells in the gill tissues.