Fishes in buried rainwater tank for mosquito control

In our region we have a lot of Tiger mosquitoes (Aedes albopictus) and during this period of the year they start to breed and we scramble for solutions to minimise the damage.

Our main concern is the rainwater tank, we have a buried 35 000 Liters concrete tank, which they love..

What we have tried so far :

- Installing mosquito netting at every opening, but there are places difficult to access where it's not a tight seal yet.
- Poured vegetable oil into the tank, to create a fine coat on the surface preventing the larvaes to breathe, this seemed to have no effect at all.
- Installed a water pump that circulates the water in the tank every day for half an hour, oxigenates the water but there are still mosquitoes.

This year we want to try to add mosquitofishes (Gambusia affinis) to try to control the larvae population and transform a problem (mosquito bites) into a solution (fertilized water).

I have to add that the tank is emptied and cleaned about every two years, and that the water is used mainly to irrigate the vegetable garden. We are very reluctant to use BT pest control like Mosquito dunk, I believe this would also kill beneficial micro-organisms in the rainwater as well as in the soil after irrigation. I'm also not so excited about pouring bleach or kerozene into the tank.

So far, I think oxygenation and temperature of the water would not be an issue for the fish. My concern is light, I plan to replace the metal lid with a transparent one, but it would still be a relatively low light situation for the fish. Here's a photo of the opening :



Does anybody have any experience with fishes in big rainwater tanks for mosquito control or any other ideas of what we could try ?

I've had success using mosquito fish, and even the common guppy. Most of my ponds are in the deep shade, but none are completely dark, as with a buried tank. But I suspect that using a transparent tank lid might allow enough light in for the fish. The fish are very effective in eliminating all mosquito larvae in my ponds.

Just for information.....BT is a naturally occurring bacterium found in the soil. It is not a poison. The BT type in mosquito dunks is specific to mosquitos. If the larvae feed on it, they will die. I have used mosquito dunks in livestock water troughs and agricultural irrigation catchment tanks. To date I haven't seen any evidence of problems using that water. But I prefer to use the fish because it is less expense, less maintenance, more effective, and a more natural approach that fits nicely with my farm philosophy,

We just put fish into a rainbarrel to eat the mosquitos, feeder goldfish and guppies.
The did not eat the mosquitos, perhaps there was too much other food available?
So I bought and used dunks. One dunk killed the mosquitos- and the fish. Or maybe you the dying mosquitos fouled the water, but considering the green muck already present, it seems unlikely.

YMMV

One of the coolest tourist sites I've ever visited is the Basilica Cistern in Istanbul Turkey. It was built in by Byzantine Emperor Justinian in the 6th century. The roof is held-up by a forest of 336 ancient columns. It once held almost 3 million cubic feet of water --- absolutely HUGE.

While it functioned as a cistern for centuries, it eventually fell into disuse, and was filled with junk and fill-dirt, stones and the like. It wasn't totally filled in, and there were still places where it held water -- some of the homes built above it would drop a bucket through a hole to get water (and to fish, but more on that later). For the last couple of hundred years, people had basically forgotten what was there underground. In 1985 they began to excavate the cistern and were shocked with the size, depth, and sheer beauty of this "underground temple". Today, thousands of tourists visit it daily. It's really cool and moody and drippy and a little bit creepy.

What is interesting is that at some point, perhaps centuries ago, someone dropped some carp down into that ancient cistern, and the off-spring of those carp have been living down in that cistern ever since. Even as the cistern went into disuse and was being slowly filled with junk and fill dirt, those fish were down there, eating something, breeding, staying alive. Carp are tough fish. Today, they keep a couple of feet of water down in the cistern, and have built wooden walkways that you can walk around on down there. But even as they excavated all those thousands and thousands of yards of junk, the carp would find a deep place to hang out.

The carp are kind of creepy -- almost totally white, swimming around in there like sharks. They've never seen the light of the sun. But they keep the cistern clean and are a part of the overall effect.

Anyhow, I like the idea of leaving fish down there and having them keep your storage tank clean.

https://www.youtube.com/watch?v=1HI_o0_Ea1M

I use minnows sold at the bait store.

William, without seeing your set up, it's hard to determine why your system failed. Because of the dengue outbreak in my area, I set up dozens and dozens of mosquito trapping micro ponds, essentially half barrels and trashcans full of water. Each was stocked with a dozen or so guppies. I have been diligently monitoring those mosquito traps for months and have yet to find even a single live mosquito larvae in any of them. So the guppies are indeed eating them all. I already had several larger ponds and catchment tanks on the farm stocked with various fish....mosquito fish, guppies, goldfish, koi, and tilapia...and all have stayed mosquito larvae free. I use dunk granules in the livestock water trough to control mosquitos because that tank overheats, killing the fish.

Guppies will not feed if the temperature is too cold or too warm. You mentioned "green gunk", so I'm guessing your rain barrel was in the sun. Thus the water could have gotten too warm for the fish to feed. Another possibility is that they had so much edible algae that they weren't interested in the mosquito larvae.

All my micro ponds are in the shade. Thus the water stays clear and the primary diet for the guppies are mosquito larvae......and their once a week piece of dog kibble that I drop in. Since the population of fish is increasing, they are apparently getting enough to eat.

Thanks Su! Yeah, there was nothing like a system, just a half stepping attempt at stocking a"pond".
We finally emptied it, found a stray handful of rice( don't ask!) and the fish, who each died after laying at the surface on their sides for a while.
I think the dog ate them after we dumped them on the rabbit poop pile...
Next time, we will do things more thoughtfully.

It's great to hear that you've had good results with mosquito fish and guppy in low light conditions Su Ba. As for BT, I'll keep it as a last resort solution, for the same reasons you quote.

Marco you make me want to visit Istambul, very cool story about the carps of the Basilica Cistern ! I remember seeing completely white catfish while diving in cenotes in mexico. Those too were living in complete darkness.

About my raintank issue, I think I'll start with the easiest : mosquitofish in the dark, and see how it goes. I'll update the thread with the results.

I got some Gambusias, they went into the tank today.

Here's a quick update, after leaving the fish alone for about ten days in the closed tank, I opened the lid today. Not a single mosquito flew out, when two weeks ago before I introduced the Gambusias I'd get a good fifty flying out immediately every time I opened. The fishes seem happy so far, I can see them swimming around.

I'll keep checking regularly, the mosquito season is really beginning just now, I'll see how it goes in the next few weeks.

As gambusia affinis is invasive in europe i recommend not using them.
The mediterranean kilifish (Aphanius fasciatus) is a native alternative.

Also several paradise fish (like Macropodus opercularis) are not invasive but a good mosquito eater,
that even hunt for the adults and not only the larave.

Furthermore almost any fish will eat mosquito larvae.