Lately I've been reading What a fish knows: the inner lives of our underwater cousins, by Jonathan Balcombe. Basically, fish are more mentally and psychologically complicated than most people give them credit for (but a lot of people in this forum will agree!). Do they feel pain? Yes. Do they remember stuff? Of course. Can they learn things? Again: of course. So I am watching my fish these days more open-mindedly. Recently I removed two of my goldfish from my main tank overnight to a breeding tank. The shubunkin who was left behind was swimming around kind of "frantically" looking for his "school" (one interpretation, although goldfish don't apparently school in a strong way). The male oranda I moved to the breeding tank seemed kind of scared there (he hid in the spawning mops). When I moved him back to the main tank, he just hung out at the bottom for a while (traumatized?), and the male shubunkin, who had stayed in the main tank, kept him company on the bottom for quite a long time. At least 15 minutes, maybe longer (see my avatar photo). One possible interpretation is that goldfish like to be around other goldfish, or at least familiar tank-mates, or feel safer when they are, and the shubunkin was "uncomfortable" when he was the only goldfish in the tank. Another interpretation is that the shubunkin missed his friend. What is the right, or the more-right interpretation? Have other people seen friendships between or among their fish?