Peter
Wolffia: Great Green Food For Rainbowfish
by Peter Unmack
Many rainbowfish keepers may be unaware that rainbows are omniverous,
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 prefered 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 similiar 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 similiar. 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, (familly 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.