I’m not sure which fish Wesen you mean, friend.

His abilities first became enhanced after he was zombified by the Cracher-Mortel, based on a puffer fish. That gave him enhanced metabolism, and what we’ve sort of called StoneForm Nick, where he appears dead. That settled down until it only came into play when Nick was either suffocated by the Santa Claus Wesen whose name escapes me, and when he began to drown whilst saving the Naiad, which is what I think you’re referring to.

The other ability he picked up was enhanced hearing after he was temporarily blinded by the fly Wesen whose name also escapes me. That also settled down but is constantly present, just not pointed out every episode.

If either of these abilities is not what you meant, send me a little more detail if you can and I’ll dig it out for you. I just can’t remember any other fish Wesen, besides the one in the episode ‘Octopus Head’ but he left no lasting mark on Nick as far as I’m aware.