Duh, have “Equator Fish” lost the ability to swim towards cooler water?
It's instinctive for them to do so. The east coast population of Bluefish is a good example. In the spring when coastal water temperatures reach the low fifties, they start appearing in our waters. In late fall when the water temperature drops, they migrate south. I caught an eight pound Blue in the surf, in 48 degree water, on December 8th of a number of years back. That's the latest I've got one here, but a few were taken on offshore wrecks until a week or two into January that year. The water's cooled a bit the last few years; my first Blue in 2013 was a few days into May. Some years it used to be the second week in April.
A cold water fish, the Whiting, when they were abundant, used to thrive in 38-45 degree water and move into the shallows during winter. They called them "Frostfish" because on particularly cold nights, while chasing bait in the surf zone, they'd sometimes be temporarily stunned by super cold wash coming off the beach. They could be scooped up by hand or with a basket or net.