Stephen, I have thought exactly the same as you. Sadness or depression are quite cruel. A couple of times her voice was more cheerful and sounded much better. I hope she can enjoy more and more this work. Anyway it won't be a problem because she can read and pronounce accurately. Bye!
According to the Australian Museum (link below), 'fish' is usually used as a plural for one species of fish, while 'fishes' refers to different species, at least here in Australia. Unless the Dutch have a different word for the latter, both should be accepted.
"Fishes" as a noun is very rare, and is usually used (to my knowledge) poetically/when quoting older sources (such as biblical) or to emphasize that you have different kinds of fish, though I think it's becoming more common to just say, 'different kinds of fish". In this case, it wouldn't really make sense for one to be emphasizing the variety of fish, so to say "fishes" sounds weird and non-standard, at least to my North American ear.
Fishes is archaic. In UK English you will see the plural probably only in The King James Bible and possibly in some classic literature. It is not wrong but would sound very unusual in modern speech except as a third person singular verb in the present tense (describing the act of attempting to catch fish - he fishes every Saturday)