NANFA-L-- Raising mosquito larvae for fish food

Jase Roberts (
Fri, 05 Aug 2005 12:18:29 -0400

Hi All,

Just came across the NANFA website, and glad to see so much excitement about native fish!

I saw a thread from last year on raising mosquito larvae for fish food ( I've been raising mosquito larvae for about a month now with very good results. My fish absolutely LOVE them (should be a pretty natural food), and I feed them almost nothing else. My juvenile bass have-in-least doubled in size in 4-5 weeks on this diet. My setup is described below. As I said, I've only been-in-this for about a month or so, so I can't say this is perfect, but it has worked well thus far.

I have one open 2-gallon bucket that I keep as the laying chamber. I basically just throw some fresh grass clippings in it to get the water good and foul. I've found mosquitoes are MUCH more attracted to this than clear water (a clear water bucket next to the foul one will get no eggs whatsoever). One tip is to put a handful of grass on some concrete and scuff it back and forth with your shoe to break up all the plant cells before you put it in the water. That makes it sink immediately rather than float in the water, and also gets the decay process underway.

Every morning I take a spoon and collect the egg rafts ( off the surface of this nasty water. The egg rafts start out white or light green and turn brown to black within a few hours. I transfer them to a series of partially full plastic shoe boxes (~1 gallon). I generally add two to three days of eggs to each box before I move on to the next (maybe 40-50 rafts total in each). The boxes are kept in the shade with loose lids that allow some air but not more adult mosquitoes. One batch that I had in the sun apparently got too warm and they all died.

Every week or so I dump my egg laying bucket to get rid of any larvae growing there, add some of the rotting grass clippings back in, and add new grass and water. Not all mosquito species lay eggs in rafts, and a few of the eggs laid singly do wind up hatching in the laying bucket. I don't want any of those to mature.

In the growing boxes, I simply add a few pinches of dried nutritional brewer's yeast (NOT live baking yeast) every day or two. I haven't read that this is a good food for mosquito larvae, but I know it's used for brine shrimp and I thought I'd give it a shot. It has worked well so far, with very good growth on most of my batches. I get the brewer's yeast for something like $1/lb-in-my local food co-op. That would be enough to feed the larvae for months. There's no question they're eating the yeast, because the growth I'm seeing would be impossible without a plentiful food source. Too much yeast does seem to foul the water, though. I'm still figuring that out. One or two of my batches have had high larvae mortality, and I'm not sure yet what caused it. It could be that the lid got pressed down tight, or it could be a scum on the water surface preventing air access for the larvae. Don't know yet.

I haven't checked the exact cycle time, but it seems like the larvae are just starting to turn into pupae-in-about 8-10 days. If you haven't seen pupae before, they're very obvious. They turn darker colored, swim differently, and have two siphons (look like horns) rather than one. I start feeding them to my fish maybe a day or two before they pupate. I harvest by just scooping the surface with an aquarium net. Any disturbance causes them all to dive, so I generally have to wait a minute or so after removing the lid for them to float back up. As soon as I see any pupae forming, I dump the entire container through a net to harvest all the larvae. This is where feeding yeast only is a major bonus. I started out growing the larvae on decaying grass clippings, but then it was tough to collect all of them from the growth chamber without getting a net full of junk. With the yeast, I dump the whole thing through the net, rinse a bit, and I have a net full of pure larvae.

I find I can keep the larvae fairly densely packed in the refrigerator for-in-least a day or two, using a shallow Tupperware-type dish of water with lots of surface area and holes in the lid so they can breath. I think there needs to be enough surface that all the larvae can have their siphons up-in-once (they breath air). I've tried freezing one batch in an ice cube tray with good results. My fish (two species of bass, sunfish, perch, and catfish) took the frozen larvae well, probably because they're very accustomed to the look of them (it's my main food).

This system of rotating through multiple containers works well for several reasons: first, I get absolutely no larvae maturing to adult. The pupal stage is several days, so as long as I harvest the entire batch when they begin to appear, none become adults. If anything, this system has the effect of reducing the local mosquito population, as all these larvae go to my fish rather than maturing in the wild. I can't see why neighbors would have any grounds to complain if I explained it (but for now I keep it fairly hidden).

The other main advantage is that each container is a single age cohort, so I'm harvesting all large larvae. When I started out using just a single container, I was harvesting a lot of really tiny larvae along with the big ones. That made it difficult to keep a colony going. If I wanted to harvest only really tiny larvae for young fish, I could harvest earlier. The other thing I'm able to avoid is having pupae mature in my aquarium, which I *really* don't want. Now that the fish are accustomed to this food, however, they generally clear the tank within minutes of feeding. There's something very satisfying about watching them devour all these potential mosquitoes...

A couple nights' of egg rafts produces thousands of larvae, and I think I get about a tablespoon or two full of packed large larvae from that amount. I currently cycle through 4 small growth chambers, which produces more than enough larvae to feed the 14 1-3" native fish I have in two aquariums.

It sounds a bit complicated, but now that I've got the system down it takes only maybe 5 minutes a day to sustain it (if that). At least for the summer, this seems easier and cheaper (almost free) than brine shrimp.

Hope this info is of some use.

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