Niko is earned on level 1-2, and opens up every once in awhile to reveal a Pearl, which can be clicked on for $250.
He is not very useful once shrapnel comes along because shrapnels bombs are the same value but he drops them more often. On the other hand though, Niko does not kill the fish with his pearls in any way shape or form. Shrapnels bombs will kill fish on impact.
they are BOMBS for goodness sake!