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SEAWATER PREPAREDNESS IN FRESHWATER AND ANADROMOUS POPULATIONS OF SEA LAMPREY
Stephen D. McCormick1 and Amy Regish2
1Department of Environmental Conservation, University of Massachusetts, Amherst, MA 01003 USA and USGS, Conte Anadromous Fish Research Center, Turners Falls, MA, 01376 USA.
2USGS, Conte Anadromous Fish Research Center, Turners Falls, MA, 01376 USA.
The question of whether or not sea lamprey are native to Lake Ontario and Lake Champlain has important implications to our understanding of their biology and to accurately model how sea lamprey have been associated with key events that altered species composition in these ecosystems over the past 150 years. This information is critical to restoring native fish species in the highly altered fish communities of the Great Lakes. It has been established in other anadromous species such as salmon that landlocking results in loss of traits associated with seawater tolerance. Populations that have been isolated for a longer period should show greater loss of traits associated with seawater preparedness. Previous research has shown large increases in gill Na+,K+/ATPase (NKA) activity and gill ionocytes in transformers of anadromous sea lamprey, similar to the preparatory physiological changes seen migrating Pacific and Atlantic salmon smolts. In this study we have examined gill NKA activity and ionocyte abundance in wild, migrating juvenile sea lamprey from one anadromous and 3 landlocked populations. Migrants from all populations were fully transformed, with large eyes and well developed parasitic mouths. Compared to ammocoetes, gill NKA activity was elevated in transformers from the Connecticut River (anadromous) and 3 landlocked populations (Lakes Champlain, Michigan and Superior). However, gill NKA activity was significantly lower in transformers from Lake Michigan compared to those from the Connecticut River. Residual ATPase activity was lower in transformers than in ammocoetes but was significantly lower in transformers from Lakes Superior and Michigan compared to the Connecticut River. The numbers of gill ionocytes did not differ among anadromous and landlocked populations. The results of this pilot project indicate that currently available tools can be used to compare the osmoregulatory physiology of anadromous and landlocked populations of sea lamprey. Although significantly lower levels of gill NKA activity were found in transformers from Lake Michigan, the high levels of gill NKA activity in Lake Superior fish does not warrant overall conclusions regarding the loss of traits related to salinity tolerance in landlocked sea lamprey. Thus, more comprehensive investigations examining physiological differences in salinity tolerance and related traits are warranted.