James - Lorsban (chlorpyrifos) is identical to Dursban, but includes a pink pigment to distinguish between the two formulations (the later was canceled for turf applications several years ago).
Chlorpyrifos is an organophosphate(OP) insecticide that targets the nerve synapse of susceptible organisms.
If you've ever witnessed an insect's reaction to OPs, they're basically unable to cancel a nerve impulse once transmitted - revealing the technical mode of action: acetylcholinesterase inhibitor (ie. their wings flap like crazy until the lights go out).
That said, check your pond for signs of aquatic insects. IF any/enough product entered the pond to cause a fish-kill, it is highly unlikely that you'd have any insect larvae (alive) inhabiting the pond.

Kelly Duffie
Cypress, TX