that's assuming a lot. remember that people disagree with your personal theories and stating them does not prove that they are fact.
I don't see how knowing that they are nutritious PROVES that the zora eat them, it is not explained what their role is. if something smells that bad, it is not too crazy to assume they might not eat them. in fact, only ralis and yeto can catch them.
jabu jabu is called a water deity, but he might not be as important as the zora think. ZD is fine without him in
TP, so either both fish do NOTHING, or they both do the same thing. ZD is unchanged in its role in the two games, the only difference is that there are reekfish instead of JJ.
let me know if there are any clear examples of JJ actually doing anything. He doesn't guard the spiritual stone, and is in an area which is defended by the zora. it seems that the zora feed and protect him, and that the only thing he might do is to purify the royal family's water source. the reekfish are bottom feeders who might provide a similiar cleansing role for the water. the water coming out of ZD in
TP is clean, just has problems in lake hylia.
also, saying the zora sell them is totally wrong. only ralis can catch them, no one else knows the secret. how can you sell something you cannot catch? in
Oot they sell fish which cannot be reekfish because they either are a different ZD(which I doubt), or are not near the appropriate rock formation, but in the shallows.
unless you can come up with some plausible idea of what JJ does, then he must either do nothing or helps purify the water.