Certainly something like egg production would follow the most predictable and longterm pattern, which is photoperiod. But I believe that actual spawning and seasonal movements are triggered by a combination of photoperiod and water temperature. It would make little evolutionary sense for them to be determined wholly by one or the other – spawning in water that’s too cold, for instance, would be likely to fail as would spawning at the right temperature too early when it’s more likely to drop again. Similarly, in the fall flatheads, while influenced by photoperiod, would benefit most by moving to wintering areas (not typically flush with baitfish) only after water temperature forces them to, and not while it’s warm enough for them to hold in better foraging areas.
I don’t think you can make any blanket statement, moreover, about how or what fish “feel”. The whole idea of “feeling” supposes an ability to cognitively process information (in humans) but fish certainly have the sensory ability to react to temperature no matter how automatic their response. Nor do I believe that fish metabolism is tied directly only to water temperature – there’s more control than that. I’m not saying they consciously control anything, just that water temperature, while having a profound influence on metabolism, isn’t the only variable and isn’t in perfect, direct correlation with metabolism. Water that’s too warm, for instance, carries less oxygen and allows for less exertion without profound oxygen debt (the reason fish are much less hardy in very warm water). A seasonally active fish is as likely to be influenced by water temperature in behavior as by other variables.
However, all that is pretty much moot since the water temp is dropping now (and the photoperiod shortening) and it’s time to start nailing the fall flats!
