Yes, that's bad. Unless you're fishing with nets you frequently just get one fish (after trying full time for multiple attempts without any luck). Since it can't be cut up into fillets, there is no way to sacrifice some of it unless you reduce its size with your teeth, and you need to be starving to eat raw fish, I think (and even then, I've roasted it first).
A fishing rod increases the chances of both getting multiple fish and getting small fish (you don't really want to waste a whole salmon, even if you were lucky enough to get two), but you only get big fish in rapids, I believe.
I've given up trying to sacrifice fish on the same day as meat, so it's been either one or the other, but it's been roasted fish.