Branching off entirely from previous discussions, I've realized that Wishiwashi is one of the most interesting concepts for a Pokemon that we've ever seen. I'd like to explore the lore behind it - to be specific, its school form.
Individually, it is not unlike a minnow - it's small and likely to have stats rivaling Magikarp and Feebas. Nothing special here - it's just a fish. But they can also come together into a school to form a creature so terrifying that even Gyarados flee from it. Now, given the school's cohesion and its resemblance to a huge fish, it's clear that they form a hive mind organism, where each individual fish temporarily loses its free will to under the same consciousness. The question is... whose mind is it? The way I see it, there are three possible theories: 1) It isn't a proper "one mind" scenario; every individual Wishiwashi simply knows where to go (like Vespiquen using Attack/Defend/Heal order); 2) the one that sent out the SOS signal gains control (like Zygarde); and 3) the combined organism has a completely different mind.
We can eliminate the first scenario by thinking from a gameplay perspective: When battling a School Form Wishiwashi in the wild, if it operated under the idea that every fish knows on its own where to go in the school, the Trainer should be able to catch hundreds of them by continuously chucking Pokeballs at the school. Assuming that catching the Pokemon ends the battle (as has always been the case), we can therefore deduce that, on some level, Wishiwashi-S is actually one being. However, it is also possible that Wishiwashi will only be catchable in its individual form (attempting to catch its School form might either simply fail or give a message similar to when you attempt to throw a Pokeball when there are two targets).
The second scenario seems more likely. After all, the school has been seen to disperse (breaking the hive mind) if it takes enough damage; this could mean that the leader can no longer focus enough to control the group. The only problems with it would stem from if two individuals send out SOS signals simultaneously (but in range of each other), and if one signals but only a few others come to its aid. In the case of two simultaneous SOS signals, what would probably happen is that they would rush towards each other, and then the stronger one would become the leader while the weaker one joins the school. This would still protect both of them from danger, as "even Gyarados flee from Wishiwashi's School form". In the case of one signaling but not having enough allies to form a school, I think what would happen is that the leader would still try to assemble the hive mind, but realize there aren't enough others to form a threat. Then they would disband and change tactics to running away.
In the third scenario, a sort of "neural network" between the brains of each fish forms, essentially creating a whole new entity. Although it's up for debate what would happen if you tossed a Pokeball at this conglomerate, it would solve the problem of two singular Wishiwashi SOS'ing simultaneously (they both assimilate into the school) and one receiving insufficient help (the neural power isn't strong enough to form the hive mind creature, therefore nothing happens). And if the school were subjected to some incident that would force them apart or otherwise disturb the order enough (such as, again, taking enough damage), it would simply shatter the network, causing each individual fish to re-awaken with no memory of being part of the school.
Obviously all of this is pure speculation; I encourage people to argue against me, add more details, or suggest alternate possibilities. Let's get the discussion going!