The 4-, 8- and 16-ray description refers to the number of terminal branches of each individual ray. If the caudal (tail) rays divide (split, branch), then divide again, you’ve got 4-ray splitting (1rayx2×2=4): if they divide 3 times, 8 rays (1×2x2×2): 4 times, 16 rays (1×2x2×2x2) and so on.

Thanks to Vicky for this description!

Generally people say two years, but I’ve also heard of fighting fish living closer to nine years.

The fish you get from your local fish shop might live less than this as they are already at least six months when you get them.