IMHO, fish are conditioned.
To me, learning is being able to ingest new information, and act on that information with knowledge already gained. So, if larger LMB could learn, why would they lose weight if they're transferred to a different BOW? Water's water, forage's forage, but still they go into decline. Wouldn't learning from the previous pond help them adapt to the new environment?
Conditioning is more about rote and rewards. You walk down the bank shaking a coffee can full of food at the same time every day, your fish will associate that with a reward. Or from my personal experience, you hand feed LMB every day for 6 months, and they get really, really attentive. You stop for a few weeks, and they're gone. Even in the face recognition article posted earlier, the archerfish "learned" via operant conditioning. Rote and rewards.
I guess the bottom line is that whether they learn or are conditioned, fish behavior can be altered. We all do it every time a feeder throws.
