Date of Completion

Spring 2014

Thesis Advisor(s)

Eric Schultz

Honors Major

Biological Sciences

Abstract

Anadromous Threespine Stickleback, Gasterosteus aculeatus, migrate from freshwater to saltwater during their early development. The timing and extent of this migration could be influenced by salinity preference. The current study was done to observe if and when salinity preference changes during stickleback ontogeny. This study also looked at the effects of historical environmental salinity on salinity preference. The fish in this study, originating from an anadromous population from Cook Inlet, Alaska, were split into two groups and acclimated to a low (1ppt) and high salinity (30 ppt). After a period of acclimation, the fish were subjected to weekly salinity preference trials in gradient preference tanks or control non-gradient tanks for 9 consecutive weeks. This time span encompassed the time when migration would occur naturally. Individual fish were tested in both control and gradient conditions through repeated trials in a paired design. Each trial lasted for four hours, and position was measured every five minutes. Results indicated that fish were more active in control tanks as opposed to gradient tanks. This result conveys a preference, indicating that fish settle when finding a preferred salinity. We found that salinity preference changed with development and that fish experienced an intensifying drive for salt as they aged. This preference was anticipatory of migration as it occurred before the timing of natural migration. We also found that acclimation had no significant effects on salinity preference indicating that environmental salinity does not affect the intrinsic drive for salt. This study forces us to re-evaluate the importance of innate factors in juvenile fish migration and encourages us to look at salinity preference over development in other populations.

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