Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Neff, Bryan D.

Abstract

The fitness of reintroduced salmonids in Lake Ontario can be reduced by high levels of thiaminase in exotic prey consumed at the adult stage. If sensitivity to dietary thiaminase differs among the three Atlantic salmon populations targeted for reintroduction into Lake Ontario, this could significantly influence their performance. I quantified the effects of experimental diets that contained high or low (control) levels of thiaminase on thiamine concentrations, survival, growth rate, and reproductive traits (sperm and egg quality) in Atlantic salmon from the three candidate source populations. Fish that consumed the high-thiaminase diet had comparable growth rates, but lower survival and muscle thiamine concentrations than control fish. Sperm count, velocity, motility and linearity, did not differ based on diet. Adult females fed the high-thiaminase diet resulted in lower egg thiamine concentrations and embryo survival. The effects of dietary thiaminase on reproductive traits did not differ among the tested populations.

Summary for Lay Audience

Atlantic salmon were once abundant in Lake Ontario but were driven to extinction more than a century ago. There have been multiple attempts to reintroduce Atlantic salmon into Lake Ontario, but these attempts have not yet produced a stable population. One potential obstacle is the presence of exotic fishes in Lake Ontario, including alewife and rainbow smelt. Alewife and rainbow smelt contain high levels of the enzyme thiaminase, which can lead to a thiamine deficiency in salmon that eat these fishes. Thiamine deficiency can lead to many negative health effects, including early offspring mortality and neurological disorders. Atlantic salmon from different populations naturally consume prey fishes that differ in thiaminase levels. If tolerance for dietary thiaminase differs among the three Atlantic salmon populations targeted for reintroduction into Lake Ontario, this could significantly influence their health on a high-thiaminase diet and the chances establishing an Atlantic salmon population in Lake Ontario. To examine tolerance to thiaminase, I fed Atlantic salmon from the three candidate source populations experimental diets that contained high or low (control) levels of thiaminase and measure tissue thiamine concentrations, survival, growth rate, and reproductive traits (sperm and egg quality). Fish that consumed the high-thiaminase diet had comparable growth rates but lower survival and lower muscle thiamine concentrations than control fish. Male sperm characteristics, including sperm count, velocity, motility and linearity, did not differ based on diet. Embryo survival was lower for females fed the high-thiaminase diet, and the high-thiaminase diet was associated with significantly lower egg thiamine concentrations. The effects of dietary thiaminase on these traits did not differ among the tested populations, albeit survival was lowest for the LaHave population—predicted to be the most susceptible to dietary thiaminase—limiting their inclusion in these analyses. Regardless, the negative effects of a high-thiaminase diet across populations suggests that source population selection is unlikely to fully overcome this potential challenge for re-establishing Atlantic salmon in Lake Ontario.

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