An alternate method of propagating rainbowfish without mops

By C. Moormann 1-20-2010

Over the years I occasionally run across some surpises in my fish room. The normal way to raise rainbowfish is to make mops and put them in with the adults and either place the mops in another tank for the fry to hatch or manually pick off the eggs. One of the problems with the mop method is that I always end up eventually tranferring snails or other pests from tank to tank. I love plants but whenever I get new ones from a plant lover I run into the problem that plant lovers don't feed their planted tanks much and don't bother to exercise snail control. They never seem to be bothered by them and if you ask them if the plants are snail-free they assume you only meant snails that bother them -- species that their loaches are keeping down in numbers are still there but are below their radar. Other animals that get going due to mop moving are hydra and planaria -- both lethal to rainbowfish fry or eggs. It seems that every couple of years I find multiple infected tanks and have to go through the trouble of salting the tanks or baking the gravel or some other labor intensive effort to get rid of them.
I recently ran into a tank with a few rainbows with plants and no mops and fry in the plants. It occurred to me that this may be a good way to breed them without mops and optimized the tank to see if it is repeatable. The tank has an underground filter and two sponge filters and with a light on almost all of the time it is growing some microalgae. The microalgae is similar to hair algae except that it is brittle and only grows in short lengths (less than 1/2 inch) in bunches and clumps. There is floating watersprite covering about a third of the top and masses of the microalgae in clumps and growing on the sponge filter (sponge and uptubes). Apparently the rainbows will lay their eggs on the microalgae. Every day I take a small bowl and suck up water from the top of the tank around the watersprite and find fry. I have a 25 gallon flat set up with a heater and 24 hour light and green water that I pour the new fry in every day and with little effort I have another generation of rainbowfish growing.
When I had my fish store I had a tank in the back room overgrown with microalgae that had gold whiteclouds that had fry hiding in the denser areas. I also had a large flat set up with sloped gravel and floating plastic plants at the shallow end that was mainly a place for guppy fry to hide. I had a dozen or so zebra danios in the tank also and when I used the bowl method to suck out guppy fry I would regularly get tiny danio fry also. I am presently cultivating large amounts of the algae to try some larger scale experiments. In a couple of my tanks (with 24 hour lighting) it develops into floating balls that tumble around in the water flow. The main tank that generated the stuff in quantity had an infestation of cone snails but I found a way to get rid of them. I put the algae in another 25 gallon flat with a couple of 6-inch koi with a 24 hour light and an airline. Over a week or two they managed to clean out all of the snails and keep the microalgae pretty clear of stuff. If the microalgae gets dirty I can reconstitute it in the koi flat. I have found small butterfly koi to be the best snail eaters -- forget loaches as they only seem to keep them down to a low level. As long as the koi can move stuff around and get to all of the gravel (no rocks for the snails to hide under) they will get all of the small ones eventually. The bigger ones can be netted out. I want to try some tetras in tanks with a lot of the microalgae to see if neglect pays off. A friend of mine with a 300 gallon planted tank had started with 10 emperor tetras and ended up with over 200 of them in the tank.