A thought for what it's worth...
Whatever the merits of an individual card may be, the specific cost to play a card is a huge factor to. Consider for a moment that a card does something extraordinary, say does 100 hp in one hit. But the cost is 40 Time quanta. Sure, the card may be way OP, but the chances of seeing several played at once is extremely low.
I know that's a huge exaggeration, but the point is valid. Though the Fish may not be on par for cost, it's cost at 5 quanta, unupped, is still rather high so it's very unlikely one will see it ever outrush decks that are based on rushing. simply because the Fish is more a control card. And consider it's effect. It can kill creatures, but over time, not instantaneously like Oty.
I honestly think the lack of dominant decks that are built around the Fish is enough of an argument that it needs no nerf. Maybe if Fish decks were running rampant in PvP and tournaments all over the place and were directly affected by the them I'd be more inclined to say otherwise. But the fact is, though they may be a powerful card in their own right, they just don't live up to the hype.