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Notes on culturing water critters for fry food.


Bender
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I have been culturing moina for a while now and thought it may be helpful to put together some notes on what has and hasn't worked for me, this should work with most types of infusoria culture. Please add you own experiences hints and tips!

Starting out.

I started out by doing your standard infusoria culture in a 3litre clear plastic jar using some lucerne hay. This was a fairly foul smelling mess for a long while, then out of the blue it started to clear up. At this point I could see tiny critters moving in the water if I used a magnifying glass. Interestingly I set up a spawn tank with plants filter and heater ( not that it ever turned on, we had a very hot summer) and left it running for a week and had almost as many critters getting around as in the smelly culture. Next time I would start with old tank water rather than a rotting mess.

Because the tank was already alive with bugs I ignored the culture for a few more weeks. It went completely clear, and one type of critter started to dominate. I thought this was daphnia, but it turns out it is a smaller version I'm fairly certain is moina. I have tried to get a clean culture of them, but so far I have only managed to make sure they remain the dominant species. I added some old mulmy tank water from my fry tank to the container whenever the water level dropped and this seemed to keep them kicking along.

Experiments with temperature and food.

After I had an incredible survival rate of my fry through the first few weeks (over 300) I thought it would be good to find out more about these critters and try to find a way to mass produce them. I moved the majority into a 20 litre tank and added some snails, leaving the rest as backup while I experimented. Research turned up the links found in this post.

In trialling both heated and un-heated tanks, I found no discernible difference in production.

The addition of an airstone is recomended by some, but I found this made no difference. I may try it again however as the concentration of critters is now far greater, and they may need more oxygen.

I tried both flour and yeast as foods, but they both lead to problems with bacterial bloom. I think this may be a viable food source, but at this small scale it was far too hard to regulate the amounts needed.

Green water has proved to be the most successful food source. I cultivate this in an outside tank with lots of snails and a goldfish. The tank is covered by duckweed, but the sun hits the side directly in the afternoon. The drawback with this has been that I've twice introduced predator bugs (damselfy larvae). To avoid this problem I began running the green water through a dust mask as I siphoned it out for use. Surprisingly this has increased my rate of cultivation, possibly because the particle size the mask allows through is better suited to the critters.

It is fairly easy to tell when more green water is needed, as the water becomes increasingly clear as it is consumed. At the moment this is happening about twice a week. I siphon out about 1/3 of the water through several layers of stocking tied on the end of the hose. This makes it slow, but leaves most of the inhabitants in the tank. A half submerged dust mask can also be used instead of a stocking, but this worked better in the small container when using a turkey baster to remove the water. Then the tank is topped up with fresh green water.

The snails have been left in my culture tank, I like ramshorns and they are breeding well in there, but I don't necessarily think they are needed for a successful culture. Further experimentation would be useful, as the waste excreted by the snails is a little annoying when harvesting the critters.

Harvesting

I first tried harvesting with a turkey baster. This worked ok, but is tedious. You can squirt the water into a dust mask to filter out the bugs, but you also end up with a lot of mulm and snail poo. I found that if I sucked up the culture water then held the baster still for a few moments letting the moina swim to the bottom I could drop them out with only a little of the water and leave the majority of the other stuff behind. I have trouble holding the baster still enough, so I cut the bottom of a softdrink bottle and sat it over a collection cup, then placed the baster in the neck to settle. A major drawback of this method is that you seem to end up with mostly adult moina, while the juveniles remain mixed in with the mulm.

My latest method is far easier, but was an accidental discovery. I had read that increasing the available surface area in the tank also increased the population of moina. I trialled a few methods of doing this, but didn't notice much difference. One was to make a ball of tulle (tutu fabric) that looks kind of like a bath puff and sit it in the tank. The moina like to sit in its folds, so I left it in there. When I decided to move the tank I lifted it out and, to avoid loosing the moina in it, placed it in a white bowl with some tank water. When I lifted it up a lot of moina was in the bowl, so I shook it around a bit to see how much would come out. There was tonnes of it! Best of all, when I tipped this water into a clear container to examine it, I could see that as well as the adults there was a cloud of babies. I have since made three other balls and alternate which ball I pull up to harvest. As you don't disturb the bottom of the tank much, there is very little mulm or snail poo.

The babies are the real prize here. They are smaller than bbs, and they won't die off in your tank so food is always available to the fry. Ideally I'd like these guys to replace bbs (probably won't happen, but I can try right?) so if you have any other ideas I'd be happy to try them.

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The information varies quite a bit. This page has the average protein of moina at 50% dry weight. But unlike bbs, the fat percentage increases from napaulli to adult, so a juvenile has only 4-6%fat, and an adult has 20-27%. I couldn't find correlating information on the percentages of fat and protein in artemia napaulli to compare this too, does anyone know where to get this?

I found pictures of the other critters I have in my cultures. They are actually both cyclops, but the females look different to the males as they carry large egg sacks. There are lots of pictures here. While there are some cyclops that can feed on small weak fry, I did not have any problems with them so assume this variety is ok. This is good news as copepods are known to be of exceptional nutritional value.

I should probably also clarify that while I would like to omit bbs in the diet of my fry, I feel it is best to offer as much variety as possible and would still include some decaped cysts. One post at The Krib suggested that the fry recognise the cysts as food (perhaps by smell?) if they are given live bbs first, so an initial batch of napaulli may be needed still. By combining vinegar eels, perhaps some microworms (they are so easy to culture it seems a shame not to use them), copepods and moina most of the nutritional requirements of the fry should be met, the addition of artemia cysts would be more like icing on the cake. They also seemed to help my fry to recognise pellets as food, so are valuable for that transition.

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  • 1 year later...

This is very traditional way, but works the best, have stopped doing it, tried once, works like magic.

Daphnia in Indonesia, they use dried chicken manure put in pail, cover for two days, put daphnia culture, and daphnia is produced in abundance. For me, happen to own guinea pig, so use guinea pig manure, works I guess, but guinea pig died so not doing it anymore. Since i did not cover the pail, I do get some bloodworm and mosquitoes, really not nice.

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