I was just collecting my daily run of fish, when I caught on to a possible experiment. I decided to catch eight fish, and see how many times I would get the same fish twice in a row. I was surprised to find out that 6 out of the 8 fish came in doubles! In other words, if I split them into pairs, 3 out of 4 sets would have the same fish twice. This is extremely helpful data; for instance, if come across a red snapper, (not too rare, but 3,000 bells are pretty helpful near the beginning) there is a big chance that your next fish could be a red snapper. Infact, twice I've got red snappers in doubles. So, basically, if you catch a fish that could get you good money, DON'T move to another spot! Look around near your current one, and maybe you could get another. (This obviously won't apply to extremely rare fish.)