Meeting Abstract

P2.139  Sunday, Jan. 5 15:30  The evolutionary consequences of staying in freshwater: seawater performance, physiological and endocrine differences between landlocked and anadromous salmon. MCCORMICK, S.D.*; REGISH, A.M.; O’DEA, M.F.; USGS, Conte Anadromous Fish Research Center mccormick@umext.umass.edu

Landlocked populations of anadromous fish have evolved frequently in some species, but the effects of this altered life history on traits associated with survival in seawater have not been well established. Landlocked Atlantic salmon usually maintain a migration from streams to lakes, similar in timing to the seaward migration of anadromous strains. Thus, there is relaxed selection on traits associated with ocean entry but not necessarily on other life history changes such as migration and niche shift. In this study anadromous and landlocked Atlantic salmon were reared under identical conditions after fertilization and examined for differences in seawater performance and its underlying physiological and endocrine control during the time of spring downstream migration. We found that salinity tolerance as judged by plasma chloride after direct transfer to 35 ppt increased in both strains in spring but was highest for the anadromous strain. Survival and growth in the first two weeks of seawater exposure was also greater for the anadromous strain. We also examined several of the critical traits associated with seawater tolerance, including gill Na+/K+-ATPase (NKA) activity, the abundance of seawater and freshwater isoforms of NKA in the gill, and circulating levels of hormones that control these physiological changes.