all of the various sailfin fish have a crazy fast re-spawn rate (less than one minute). They occasionally act as place holders for other mobs. The roamers are generally PH for Piranhas and I have seen static sailfin (wont leave the room they are in) take the place of sharks.
____________________________
Maulis Thefool, Ranger of the 86th season on Firiona Vie...
These are fish that range form lvl 1 to 1. The danger with them is that if you make them mad, they blow up on you. They literally explode doing anywhere from 300 to 400 dmg. You also get a faction hit for Phingel Atropos. But, hey, look on the bright side! Their loot is fresh fish! :\