Some people worry that a backyard pond will be a source of
mosquitoes. Pond owners
often stock mosquito fish to reduce the likelihood that
mosquitoes will use the pond to
reproduce.

Mosquito fish are tiny, about an inch long or less. They
don’t lay eggs. They give
birth to free-swimming young after a gestation of a bit less
than a month. The young grow
fast and begin reproducing in a few months. It doesn’t take long
for them to saturate
their habitat.

Mosquito fish, Gambusia affinis, are a good choice for
small ponds without fancy
water-quality gear like aerators and filters. They can live in
shallow, scummy, poor
quality water.

As a test of their effectiveness, I stocked one of two
identical ponds with mosquito
fish last summer. The other I left fishless.

On Nov. 19, I hauled out about 5 gallons of water and bottom
detritus from each pond. I
strained the water through a piece of cloth and put the contents
of each into white bowls
so I could see the insects and other pond life.

Sure enough, the fishless pond had a population of mosquito
larvae. I failed to find
them in the pond with mosquito fish.

Besides the mosquito larvae, the fishless pond had midge
larvae and Eristalis
larvae. Eristalis is a fly larva that has a long tail
like a breathing tube, which
it extends to the surface as a snorkel.

The fishless pond also had frog tadpoles. Those were
interesting. I wonder if the
mosquito fish had prevented frogs from successfully reproducing
in the pond by eating
newly hatched tadpoles. Next summer I’ll have to check that
out.

The bottom line is that mosquito fish can keep a pond free of
mosquitos.

Can other fish do as well? Yes, many kinds of fish eat
mosquito larvae, especially
sunfish of various kinds. These fish will need a higher standard
of water quality,
however. Many predacious fish will eat mosquito fish along with
mosquitos.

Will ponds without mosquito fish make life unbearable for you
by giving rise to huge
swarms of vicious mosquitoes?

Mosquitoes are often in backyards without water nearby. Until
this year I never had
mosquito fish and was never particularly bothered by mosquitoes.
Having a mosquito
fishless-pond may not make a noticeable difference.