A simple trick which seems to work to attract a lot of Culex mosquitos to a tank so that you can feed killifish fry with their larvae developing from the eggs they lay in there, of any age you might need:
Add a small amount of wheat flour and yeast to the (dechlorinated) water of a 80L basin partly shaded. If the mosquitos are around, soon you will even smell how many they are in there. The flour was my idea, the yeast Milan‘s.
For a while I try to raise small fish without much Artemia. It decays when not eaten, it can feed predators of the fry. I’m down to two to three feedings of Artemia now, without much mortality. From day one, I add a mix of living invertebrates to the tanks, as in the video. Chaoborus larvae are removed from the mix, large Culex as well. The tank gets some tap water so that the water does not remain too soft and abundant java moss. Per day, some extra (rain) water is added and food if necessary. For this extensive setup, population density is critical: the tank surface per individual should be some 100 square centimeter. So for really large groups, I need to switch back to an intensive setup with water changes etcetera.
Not easy to get decent pictures of detritus worms while they move around in my jar cultures. Here a collage of a rear end and a front end. The pictures were made with a dinolite USB microscope. All the small specks in the pictures are alive as well. Will need to use a different setup to photograph these, probably a water droplet, and a lot of patience.
I’m experimenting with cultures that I can basically pour into the fish tank entirely, once “mature”. The culture I mean. For now I’m trying things in 0.5 glass jars at home on a shelve with moderate daylight. I’ve added tap water, a few Daphnia and small detritus worms that I scooped from a rainwater drum in my garden. On the bottom there are some specks of cocopeat and I fed the system a few times with dried yeast. So far, the Daphnia multiply, the worms too, the yeast seems to persist. Things go well. One jar had a solution with some drops of coffee creamer standing in it for a week before the water was replaced and the other animals were added. The cream had created a film on the glass in which the worms indulge. Next challenge: Massively increase the surface where the film can settle which hopefully increases the worm fraction. The nice thing about that is that I won’t pour the surface covered with film into the fish tanks with the feed. On the photo: few of the worms. If you magnify them a bit, you can see their chaetae.
Sometimes I have tubifex that can’t be fed to the fish immediately. I used to chuck it into a tank, where it would do well, but often it would be difficult to recover. Then suddenly I remembered a remark by Herman Meeus, how people used to “fish” tubifex by putting a burlap sack on top of the substrate. I applied the technique to my tank, and it works! Let’s see if this can be the start of a new food production method…
Live food, the more there is, the better. Some of my attempts to culture Moina waterfleas failed by copepod invasions or other unexpected events. I now raise them in jars with Pistia stratiotes plants. These are just standing in the windowsill and go fine so far. I do see some copepods in the jars, but they don’t seem to take over the entire culture.
Another way to grow blackworm (Lumbriculus variegatus) seems to be on Japanese filter mats. I have a piece of that about 40 by 20 cm in a plastic tank outside. The water level is currently 15cm. The worms have settled in the mat, and I can regularly collect a clump of worms from each corner where they also accumulate. The tank has been outside at temperatures from 1 to 20 degrees, so far without problems. The food I use are spirulina tablets, but I will try to replace that by spinach or other leftover green vegetables from the kitchen. I do take care to regularly remove all other organic material than the food. The worms seem to grow larger than in my indoor culture.
Another culture of blackworms is running for two weeks now, and the worms evidently multiply, even at 17 C degrees. It is built from an I*ea storage box with a tray inside. The tray is perforated to allow a pipe to pass (right). A sponge filter with pump takes water from the bottom compartment through the perforation. Water returns from the tray to the bottom via the handle in the tray, which is partly blocked with filter foam. My estimate is that this system contains 20 liter of unchlorinated tap water, and that I will be able to feed at least five tanks from it. The worms live on an around dice of filter sponge (large pores). Food: pellets with a high percentage of Spirulina. Water changes: none yet, but I plan partial changes at 15 day intervals. A third system is already in preparation, more news soon I hope….
Another culture which has taken off well, thanks to the excellent advice of João Mourato, are vinegar eels (Turbatrix aceti). In a small plastic pot with some air holes in the top, add a mixture of oatmeal porridge and vinegar in a layer of a centimeter in total. I briefly boil the oatmeal in water to make the porridge. The vinegar I use is apple vinegar without sulfites added. I add not too much vinegar. When I taste the medium (before adding the starter worms), it tastes slightly acidic, but not too much.
The worms will crawl up the walls of the pot, where you can harvest them very easily. In retrospect, they might be just microworms (Panagrellus redivivus), since it has been easy to maintain them without vinegar also, will check…