Wolffia: Great Green Food For Rainbowfish
by Peter Unmack
Many rainbowfish keepers may be unaware that rainbows are omnivorous, meaning they eat both animal and plant material. Providing sufficient animal material is not a problem, unfortunately though, some aquarists may fall a little short in feeding them their veggies. There are several ways of overcoming this deficiency without going to too much trouble.
My preferred option is to feed wolffia, (family Lemnaceae, genus Wolffia). This is the worlds smallest angiosperm or flowering plant at around 1/16 by 1/8th of an inch or 1.5 by 3.0mm. This plant apparently has a world wide distribution, although, it can be hard to come across. The most likely place to find it is in still water habitats along rivers, (i.e. billabongs, lagoons, swamps and oxbows, in other words habitats isolated from the current most of the time). Wolffia is similar in many ways to the better known duckweed, (family Lemnaceae, genus Lemna) and can be cultured in a similar way. I usually grow it in 3x4x1 ft ponds in which I also culture daphnia or something similar. Only a few individual plants are required to start a culture, although the more you start with the quicker things will get going.
Basically that's all you need to know to get started. However, there are a few things that can be done to boost production. All plants need a source of nutrition, thus it helps to add rotting leaves, only a few are required, some experimentation will soon teach you what levels are adequate without fouling the water. Plenty of sunlight is desirable, if algal problems develop then there is probably too many nutrients present. I don't know what the temperature tolerance of wolffia is, but I had no problem maintaining it in Melbourne, Australia where daily maximum air temperatures may reach 40°C (104°F) and the minimum may get down to freezing. Wolffia generally grows best in the low to mid 20's (70’s °F) but once your culture is up and running you should have more than enough for most of the year. One trick is to cover the ponds during Winter, (preferably with glass to let the light in) as when rain hits the wolffia a significant proportion of it will sink, (probably an adaptation to stop it being washed away). (Ed. note: I can’t resist commenting at this point. I live where outside ponds are frozen most of the year. Well, at least the wolffia will not sink. Also, wolffia is native to Michigan so it is hardy to our winters.) When it sinks it does not die, it is just harder to collect. If you have problems with sinking wolffia a little trick that I found was to stir up the pond, this would usually cause some of the wolffia to float, once I had collected what had come to the surface I would stir things up again until I could no longer get any more. Always maintain a pure culture of wolffia, do not mix duckweed or any other floating plants in with them as they are typically inferior foods and they will overtake the wolffia.
Also, I prefer to avoid snails unless you want them throughout your fishroom. To feed it to the fish I just collect it of the surface of the water with a fine net and put it in the aquarium. The quantity you put in doesn't really matter as the fish will eat it as they desire and it probably won't last very long anyway, (depending upon how many fish you have of course). There is some variation in which species of rainbows will eat wolffia, i.e. species such as all the _Melanotaenia splendida_ subspecies love it, while some others are not quite so keen, although, I am yet to see a rainbow that will not eat it. Other plants that make suitable rainbow foods that I don't believe are as good as, but could be used instead of wolffia are, duckweed, riccia, (family Ricciaceae, genus Riccia) and probably azolla, (family Azolaceae, genus Azolla). Of course rainbows don't mind eating kitchen scraps such as par boiled spinach, silver beat and probably any others that any other fish will eat. However these have the disadvantage of being dead and fouling the water, you will not have problems with uneaten food if you feed your fish live plants. Best of luck finding some wolffia now!
Reprinted from The Rainbowfish Times, journal of The North American Rainbowfish Study Group. Volume 8(3): 15-16. 1994.