Yes, I was wondering about that myself.
It's like the differences between the kitchen dishes and the animals themselves:
- pork vs pig
- beef vs cow
- veal vs calf
- mutton vs sheep
- venison vs deer
It's mainly down to the "noble" Norman (French) invaders of England who used French terms for the culinary dishes versus the terms used by peasant Englishmen who tended the living animals.
But I do wonder about Pez dispensers.
I've never been dispensed a fish...
Because when you say (where was the fish). You are speaking of only one fish.
You can try reporting it, but for me, fish is usually the plural for fish. I would say we caught a lot of fish today or the fish are biting today. I could maybe see myself using fishes when I'm trying to talk about different types of fish or something, but even then, fish feels more natural. I definitely wouldn't use fishes in this sentence.
That's part of learning a language there has to be a balance between word for word and translating into something that sounds more natural. There is no right or wrong answer here per se, which is why you can report it. I just try to stay as close as I can to word for word unless the English doesn't sound right to me. This sentence is also teaching you that although they use the plural for fish in Spanish we use the singular for the most part