I was going to test the output of Fish Ponds to see how many Preserve Jars one would need to have dedicated to aging Roe (and profit of course), however upon attempting to toss a legendary fish into a Fish Pond, I received a message to the effect of "That fish won't be happy there" or something along those lines. But upon further inspection, Roe and Aged Roe are already in the game for all the legendary fish? That said, assuming the other legendary fish give the same message, why wouldn't we be able to put legendary fish in the Fish Pond if the related products created by doing so are already in the game? You don't need multiple fish before they start reproducing, and emptying the pond doesn't give the fish back to you. Based on all of that, there doesn't seem to be any reason, from what I can see, for not letting one throw the legendary fish in the pond. Edit/Update: Busy over the weekend, still trying to get a Lava Eel pond to max capacity. Could stuff it after every increase quest, but also want to know how long this takes if you only ever put one in. I imagine someone probably already did this over the weekend but oh well, I'll keep at it regardless. Taking longer than I thought, though... Fish are definitely not like rabbits...
Legendary fish are explicitly excluded by code, most likely as a design or balance decision from CA. Only he could accurately answer the question of why. Also, there is only 1 base type of roe/aged roe that gets dynamically renamed/recolored based on the fish type. The game supports any fish (or indeed even non-fish items) for roe, which makes it quite flexible to handle both future updates and mods.
If nothing else, my understanding is that if you fill a fish pond to less than the total capacity, the fish will eventually reproduce, and CA obviously doesn't want people getting more than one legendary fish of each kind (as shown by him getting rid of the ability to catch more than one Legend). Of course, that could also be solved by just never letting the legendary fish reproduce in the pond, but IDK.
You can also use the fish pond to produce Coral, which might be useful in making a steady supply of Deluxe Speed-Gro. It will all be of normal quality, but that doesn't matter for the crafting recipe.
Sorry for late reply, if you remove fish from the fish pond you don't get any of them back. That could be a/the reason why, but you could also just give the player one fish back from the total population, since it required they put one in to start the population in the first place. -------------------------------------------------------------- Like was already said earlier, only CA can really say why... Not that I don't enjoy speculation, if anyone else was wanting to toss an idea around.
Oh? Wasn't aware of this, for some reason I was under the impression that putting them in there was a permanent decision. Guess that explains why there was no confirmation popup.
