Had a fish fry with some buddies a couple weeks ago. Picked up some catfish fillets from Costco. Buddy also brought some red snapper chunks from one he caught. Used same batter (Louisiana Spicy and Crispy fish fry). The batter was much more flavorful and spicy with the snapper. The spice on the catfish was almost non-existent. So for the food science gurus, what causes this?

Could also have to do with the higher fat content of catfish. I guess you're going to have to run an experiment with two batches of catfish.

Was the catfish fresh or frozen?

My thought is, the snapper are in salt water, I've noticed sometimes that these fish have more flavor vs fresh water fish.

We caught some blue cats in brackish water before when trout weren't biting. They had a much better flavor compared to lake or river catfish.

It was fresh. Thinking it has something to do with the fat as mentioned above. Everything was prepared exactly the same way.

Were the fillets seasoned with salt after they came out of the fryer? Sometimes people forget to do that.