I had one betta in particular, a rescue, who I owned for several years. One day I started to notice his downward decline, and after trying multiple courses of action to diagnose and treat his problem, I eventually became resigned that he was simply old and dying. On his last day I was at home and would come sit by the tank frequently, knowing that I didn't have much time left with him. Each time he spotted me he would slowly and painstakingly float over the the corner nearest to where I sat (regardless of how far it was from where he was originally situated) and settle down as close to me as possible, just looking at me. At this point he hadn't been eating for probably a day and a half, so I know he wasn't simply associating me with food- he obviously wanted to be near me for other reasons. It was absolutely heartbreaking, but certainly was proof to me that he- dare I say it without being accused of anthropomorphizing- was capable of having feelings in some way. He certainly wouldn't have exhibited this behavior if he was only motivated by food, shelter, and reproduction as some assert about animals, and fish in particular. It truly was an experience I will never forget.
Do fish have memories? Of course they do. Although they definitely don't have cognitive capabilities as advanced as humans, it is a mystery to me why people are so set on trying to make this great divide between animals and people, especially when we all share the same fundamental biology. Fish neural tissue is composed of the same aggregate of cells as human neural tissue, nerve impulses are resultant of the same fundamental process in all animals, and even aspects such as immune function and cellular respiration are nearly identical throughout the animal kingdom, humans included. We are all the same, just at different levels of development...finding that fish have memories that span several months to half a year does not surprise me.
20 gallon long: 3 adult Neolamprologus similis + about 11 fry of various ages; low light planted tank
20 gallon long:2 freshwater dwarf puffers (Puff Puff and Poofer); medium-light planted tank
10 gallon: 1 male betta named Wormy; low light planted tank
10 gallon: 1 male betta named Dante; low light planted tank
2, 5.5 gallon tanks that are currently empty (I see more fish on the horizon