Notes On Fry Food Cultures by Mark O'Connor

 

 

Volvox is a giant infusorian, a slow swimming colonial algae but vastly larger than those species like Euglena that are found in ordinary "green water". Adult individuals or colonies are visible to the naked eye (against a good light) as green or pale green globules, almost perfectly round. Their lack of projections and the fact that they do not thrash around like microworms or vinegar eels makes them suitable food for baby egg-layers. The fact that they move slowly to the light enables them to be bred in a vat and concentrated for use.

 

The Encyclopaedia of Live Foods says that they are found in iron-rich waters, usually under a layer of duck-weed (ie. not in full sunlight) and they can coexist with daphnia. It comments that during the session when they swarm "fish fry grow fat".

 

My culture appeared last winter as an almost pure culture in a one gallon (5 litre) glass jar left out against the north wall of my house. (There was a half teaspoon of salt in the water to make it less likely to freeze and crack the jar, although the top does freeze fairly often. I added some chelated iron after identifying the culture, and the odd drop of aquarium plant fertiliser since). There was a thick layer of duckweed on top, and the jar was heavily shaded from overhead sun, but takes in quite a lot of slanting light through the sides especially in winter. Last summer daphnia and cyclops re-appeared and seemed to eliminate the Volvox, but it re-appeared recently as a fairly pure culture.

 

Not much is known about this Australian(?) species of Volvox. I would urge fish breeders to experiment with pipetting out a pure culture and experimenting to find out the temperature and light intensity in which it can best be cultivated. It has great potential as a trouble free permanent fry food. If cultivated in bulk, it might also be ideal food for young live-bearers. If it can be cultivated along side ordinary "green water", the result might be a onestop fry food for egg-layers. I can supply Volvox cultures to any member interested in them.

 

This is an outdoor culture of Euglena-like organisms that has stayed green for a couple of years in a large 40 litre white plastic container in the full sun on the north side of the house (it often ices over). I feed it with osmacote slow release fertiliser pellets, about a dozen every three months. In summer it is bright green and up to 40% of it can be harvested daily for feeding daphnia or very small egg-layer fry.

 

Incidentally, a tip when using microworms as fry food. Swirl them in a tall glass jar away from heat or light that might create currents. In five minutes they will all fall to the bottom, wash, refill and swirl. This time allow only a minute or two for the adult worms to fall to the bottom. You can then pour ofr the smallest worms for very small fry.

 

And a tip for vinegar eels. When using coffee filter papers to strain them out, fold over the seam at the bottom, since this is where most coffee filters leak, being poorly stitched.