Salinity preference in killifish (Fundulus spp.)

Abstract

Fish normally live in salinities ranging from 0 ppt (freshwater) to ~35 ppt (seawater) but most fish can only inhabit fresh or saltwater making salinity a main factor in determining their distribution. While euryhaline fish can tolerate the osmoregulatory challenges that occur with changes in environmental salinity, they exhibit preference for particular salinities. The Common Killifish (Fundulus heteroclitus) is a small estuarine fish that normally prefers brackish water (~20 ppt). In brackish water where they overlap, F. heteroclitus can co-occur and hybridize with Banded Killifish (Fundulus diaphanus), a fish that prefers freshwater. The first goal of this thesis was to set-up and optimize the Loligo® ShuttleBox system to measure salinity preference of the two species to compare this new, more accurate system to previously published data. The second goal was to determine the salinity preference of wild juvenile F1 F. diaphanus x F. heteroclitus hybrids. The system consists of two connected choice tanks and a video-tracking system that allows salinity to be automatically increased or decreased depending on fish location. I predicted that the salinity preference of F. heteroclitus would be 20 ppt, F. diaphanus would be 1 ppt, and wild juvenile hybrids would be ~9.5 ppt, consistent with an additive genetic basis for salinity preference. Future work should include completing additional trials using wild F. heteroclitus, F. diaphanus, and hybrids as well as lab bred pure and reciprocal F1 hybrid crosses to gain a better understanding of the role of parental effects on salinity preference.