Effect of Increased Salinity Concentrations on Gill Morphology and Gene Expression in Redear Sunfish (Lepomis microlophus)

Changes in gill morphology have been observed in certain species of freshwater fish in response to increases in salinity. The purpose of this study was to observe the salinity tolerance and the osmoregulatory responses through gene expression and changes in gill morphology of a local freshwater fish (Redear sunfish, Lepomis microlophus). Four treatment groups with six fish each were designed to examine both short term (24 hr) and long term (96 hr) exposure to hypersaline water (17 ppt). Fish exposed to 17 ppt saline water had significantly increased plasma osmolality and interlamellar cell mass to gill length ratios compared to control groups. Early testing indicates the expression of genes associated with stress and osmoregulation as well. In total, Redear sunfish exposed to increased salinity seem to display some level of osmoregulatory behavior as demonstrated by gill tissue changes and expression of relevant genes, however, fish were unable to correct the osmotic change by 96 hours sustaining dangerously high plasma osmolality