Tropical Fish (Ornate Butterflyfish) spawned by itself and not in a group of 8

I was flying around my world when I noticed that a Tropical Fish spawned by itself. I decided to check if that was possible and found that they spawn in groups of 8 and not one. This could effect more Tropical Fish then just the Ornate Butterflyfish but that was the only one I found. I have a seed where I found the Black Tang also spawning alone. The Seed is -8825165825524102318 and the cords are 516 60 1011