Getting your chosen fish to pair off and spawn may provide a real feeling of success to an aquarist, but the next step is just as criticalgetting the resulting fry off to a good start. There’s many a peril between a clutch of fertile eggs and a tankful of healthy, thriving adult fish.
Consensus among successful breeders is that the first tank for fry should be small. Newly hatched fish are usually unable to swim very far or very fast. A fairly small, shallow tank or container keeps fry and food in close proximity. Young fish usually have good appetites; they must eat frequently and heavily in order to grow. Fish fed only once or twice a day will rarely become large, robust breeders, so feed them as many as half a dozen times a day, if possible. As the fry grow, they can be moved to larger quarters.
The disadvantage of small quarters and frequent, heavy feedings is rapidly accumulating high levels of pollution from wastes and decaying foods. High levels of nitrogenous waste also act as growth inhibitors, so frequent partial water changes (up to 50% several times a week, or even daily) are essential to maintain healthy growth rates in the fry.
Good filtration can be as important as regular water changes. Sponge filters have proven best for use with small fry, since they can’t be sucked into them, and often feed from microorganisms growing on the filter surface. Also useful are inside, air-driven box filters. Small fry often swim into such filters and feed on the trapped food particles and microorganisms there, so it’s best to leave off the lid, to prevent fry from being trapped.
Ideally, food source(s) for the newly hatched fry should have been planned for well ahead of time. Young fish need a variety of foods to grow their best, but providing it is not as simple as it is for adult fish due to the small sizes required. Dried and powdered foods can be used, both crushed adult foods and commercially prepared food for fry, but there’s no substitute for live food. There are a number of possibilities, depending on the size of the fry and the space, skills, and capabilities of the aquarist.
For all but the smallest killifish fry, the most easily available live foods are baby brine shrimp (Artemia salina nauplii), microworms, and vinegar eels. Microworms can easily be cultured by the aquarist using cornmeal slurry or cooked oatmeal as a base; vinegar eels grow without care in a mixture of apple cider vinegar and water. Baby brine shrimp can be hatched out in the fishroom with little trouble. If available, baby daphnia may also be used.
However, some fry are so tiny that even these small foods are too big. For such babies, greenwater, infusoria, or yeast or egg yolk infusions may be necessary.
Greenwater is no more than single celled algae, and can be cultured by adding algae from the aquarium or a few drops of liquid fertilizer to aged aquarium water and leaving it in a sunny location. Feed a small measure of the liquid to the fry.
Infusoria are small, single-celled animals such as euglena, paramecia, or amoebas, or microscopic multi-celled ones such as rotifers. To aged aquarium water add crushed lettuce and the culture starter. When it gets cloudy it is ready to feed, as above.
Yeast Infusion: dissolve some baker’s yeast in aged aquarium water. Feed immediately.
Egg Yolk Infusion: Hardboil an egg and remove the yolk. Mash to a fine consistency, then swirl in water. Feed small amounts of the resulting cloudy liquid.
As fry grow, they may “graduate” to larger and more varied foods. Remember, though, that the more variety in the diet and the cleaner you can keep their quarters, the better they will do.
You’ve managed to bring the clutch of eggs and the newly hatched fry safely through the early weeks of growth, and they are coming along nicely. Now comes one of the harder tasks, sorting and culling the fry. Although some aquarists seem driven to “raise them all,” sorting and culling are necessary tasks.
Sorting. Most broods contain a few individuals that grow more quickly than the others. This disparity in size can lead to harassment and actual predation of smaller individuals by the larger ones. Sorting fry by size can thus result in more fry successfully raised. For the same reasons, it is a poor idea to mix broods of different sizes and ages together.
Culling. Few broods also fail to include some specimens that are obviously weaker, less healthy, or that are deformed. In nature, these individuals would rapidly die from predation. In the more protected environments of aquarists’ tanks, we must be responsibile for selectively destroying them. These culls can either be euthanized (one humane method is to freeze them in a small amount of water), or (if they are not diseased) to use them as feeders for other fish.
Following these general steps, you should be able to have the satisfaction of raising a group of healthy, well developed young fish. From these you can then proudly and confidently select your future breeders, your show fish, and those you will sell to other hobbyists.
References: Marshall E. Ostrow, “Raising Healthy Fry,” Tropical Fish Hobbyist, November 1980, pp. 29-38.
Bill Volkart, “Feeding Fry: How Big is Too Big?”, Tropical Fish Hobbyist, June 1994, pp. 78-81.
G.C.K.A. Newsletter, Sept/Oct 1998