Try this: ( lets pretend your trying to spawn a fish with class named Fish)
make a timer. and decide how long you want to wait before each spawns
when the timer reaches a certain point in time that you decide
Actor fish;
Fish fish = new Fish();
addObject(fish, X you want, Y you want);
I dont know how to make a timer but there are programs you can look at on this site to find out how im sure.
Thanks but what I want is like instead of a timer I need like a REspawn not just another spawn.
Ex:
If crab gets eaten by lobster, then crab respawns automatically without need of resetting world.