Do fish have enough brainpower to work together? Yes*. Researchers in Queensland found that in pairs of rabbitfish, individuals take turns guarding (adopting a vigilant stance, on the lookout for predators) while the other looks for food. Fish who have a partner to help forage go deeper into crevices than solo fish, indicating that they are willing to "take more risks" when they have another individual looking out for them.
This is called "reciprocal cooperation," which historically has been assumed to be characteristic of highly social, intelligent animals (birds, primates, and the like). Obviously, fish are capable of cooperating reciprocally, as demonstrated by this research; this, with a wealth of other evidence indicating complex sociality and cognition, may prompt "a shift in how we study and ethically treat fishes" (quote from David Bellwood, who was involved in this study).
What goes on in the exceptionally large brain of the elephant-nosed fish, a species that produces electric fields to navigate murky waters? What about threespine stickleback fathers, who put on deceptive displays to lure other sticklebacks away from their eggs (which are considered tasty treats by unrelated sticklebacks)-- do they understand that they are tricking their peers, or is this behaviour somehow innate? Even goldfish-- who are constantly ridiculed for having short memories-- can actually remember details (such as colour of a reliable food tube) a year later.
And of course, one fish has shown incredible cognitive ability: social learning, tool use, nuanced cooperation, written language, the development of rudimentary governments, and even some limited understanding of abstract physics. What fish is that? Humans.
They found that as one fish assumes a stationary, upright position in the water, their partner will feed. Compared to fish hunting for food alone, fishes with a foraging friend take more "consecutive bites and penetrate deeper into crevices", which suggested there was a significant advantage to the behaviour. "This behaviour is so far unique among fishes and appears to be based on reciprocal co-operation between pair members," Dr Brandl said.