Q: Down here in central Florida, our seatrout become lethargic much of the winter, and even die if the water gets really cold. Yet at the same time, my buddies up in Virginia are bundling up in the dead of winter and catching some huge gators (trout) in waters that must be far colder. How does that happen? I’m sure it’s the same species. Can that degree (pardon the pun) of acclimation account for such a discrepancy?
A: Spotted seatrout, Cynoscion -nebulosus, range from Florida to New York, so the fish in question could well be the same species. Assuming this is the case, here’s what’s likely responsible for your observation. Animals most often die from cold temperatures because the chemical reactions necessary to maintain their cells slow down as the temperature drops, until the reactions become too slow to keep cells — and the organisms they comprise — alive. Cellular reactions are catalyzed by enzymes, which are protein-based regulatory molecules that are also temperature dependent. Members of a single animal species living in different geographic areas may have slightly different enzymes — termed isozymes or isoenzymes — which perform the same functions but work best at different temperatures. In other words, while the basic chemical reactions that occur in the cells of spotted seatrout from Virginia and central Florida might be the same, differences in isozymes could make individuals from the northern portion of the species’ range better adapted to cooler water than those from the south, and vice versa. A widely distributed species may be divided into populations that are best adapted to different environmental conditions. Factors including the rate and duration of water temperature change in each area also could play a part.
— Ray Waldner, Palm Beach Atlantic University, Florida
Photo by Matt Lusk
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