You are really lucky, then. My sim can barely catch 5 deathfishes per night (0:00-5:00), even though he has all the challenge stuff completed and is using angelfish as bait. This is because he keeps stopping every 30 sim-minutes due to passing ghosts (they still love leaving the graveyard). For me, it's better to catch deathfish on a stocked pond.
This got me thinking, if we stock the graveyard pond with deathfish (at the other side of the pond, not the same spot it already spawns), will we be able to fish it all day long? This would make it more realistic than having a pond of deathfish in your backyard, or random deathfish swimming in the park lake.