Q. I would like to obtain live cultures of both brine shrimp and Daphnia. However, I am having trouble finding anything but frozen brine shrimp or Daphnia. Any help that your excellent magazine can give me will be greatly appreciated.
A. Your letter does not indicate how you intend to utilize the brine shrimp. That is, do you want adult shrimp for food for your mature fish or brine shrimp nauplii as a source of food for baby fish? I will therefore deal with both situations. I believe that newly hatched brine shrimp nauplii are probably the most important source of nutrition for baby fish that the hobbyist has available.
Brine shrimp eggs are available in most good tropical fish stores. The eggs originate from several different locations in the country. Therefore, hatching instructions vary slightly based upon the optimum water quality needed for the particular brine shrimp eggs you are using. Specific instructions can be found on the container the eggs are packaged in.
The basic formula is seawater plus some special trace elements for each particular variety. The most effective method of hatching is to put a teaspoonful of eggs and 2 liters (there are 3.785 liters per gallon) of hatching solution in an inverted cone with an airstone at the lowest point (I use a plastic soda bottle with the bottom cut off and an airstone in the neck). The time required to hatch the eggs varies with the temperature of the solution. The warmer the water, the faster the hatch.
After the hatch period has elapsed, the airstone is removed or turned off and the solution is allowed to settle for about five minutes. The unhatched eggs will settle to the bottom, the discarded eggshells from those eggs that have hatched will rise to the top and the shrimp-laden hatch solution can be siphoned from the middle of the container.
The nauplii should be netted out of the solution with a very fine net and rinsed in freshwater before feeding to fish. Do not add the hatching solution to your aquarium because the salt can harm some species of freshwater fish and the extra protein from the eggs shells can pollute a marine aquarium. The nauplii can be used as food for both freshwater fish and marine fish and invertebrates.
Live adult brine shrimp are a good supplement to the diet of almost all small- to medium-sized tropical or coldwater fish and are available in many of the larger aquarium shops throughout the country. Unfortunately, live adult brine shrimp are also an expensive source of food because of the high transportation costs. It is often cheaper to buy a supply of eggs and hatch and raise the resulting nauplii to the desired adult size. The primary difficulty with this is the vast amount of space that is necessary to raise sufficient shrimp to feed a large collection of fish.
I know of several hobbyists with limited needs for adult brine shrimp who keep an old, enamel bathtub (a small plastic wading pool works almost as well) in the backyard for the purpose of raising nauplii to adult shrimp. They start off the year by filling the tub with seawater at a salinity of 1.020. To this they add the daily leftover eggs and hatching solution from their brine shrimp hatchery. Actual breeding of the brine shrimp seldom takes place outside, although sustained warm weather will allow the production of live young. What the hobbyist must rely upon is the supply of nauplii that are still in the eggs and the small portion of hatched nauplii that the hobbyist was unable to separate from the empty eggshells. Under normal circumstances, this is enough to keep the tub full of growing shrimp.
Twice a week the hobbyist must feed the tub with an infusion consisting of a package of dry yeast and a hard-boiled egg yolk that have been mixed with a cup of water in a blender. After a few weeks there is a steady supply of adult brine shrimp at various sizes for any special feedings that are deemed necessary. The tub is emptied and cleaned yearly to get rid of organic detritus that builds up. (Note: If the number of adult shrimp produced is insufficient, an airstone can be added to the tub to dramatically increase production.)
Daphnia are a little more difficult to get started with because you cannot run down to your local aquarium store and buy a can of Daphnia eggs as you can with brine shrimp. However, part of the mystique of Daphnia is the challenge of obtaining the culture starter. Live starter cultures can be found in your back yard (or a small pond near your house), in another local hobbyist’s fish room or they can be purchased through mail-order outlets, which can be found in the classified section of this magazine or from the biological supply company that your local high school buys its classroom supplies from.
Rearing Daphnia in quantity can be done much the same way as rearing brine shrimp, with two differences. There are no Daphnia hatcheries to be emptied into the tub to keep populations high, and the tub is filled with freshwater instead of seawater. Daphnia, when protected from predators, can develop large populations in small bodies of water if there is sufficient food to nurture them. The hobbyist can aid in this by keeping the water temperature between 68 and 70 degrees Fahrenheit, using an airstone to increase circulation and oxygen/carbon dioxide exchange, and feeding with an infusion of hard-boiled egg yolk and garden peas mixed in a blender. It is not necessary to use the large bathtub method. I was quite successful at rearing Daphnia in a series of styrofoam shipping boxes. I had one box for each day of the week. I would collect all of the Daphnia in the box, return a large enough quantity to provide breeders for the following weeks’ needs and feed the rest to the fish.
There is one caution that needs to be mentioned, and this is as good a time as any. Daphnia and brine shrimp are supplemental foods! In other words, these foods should not be fed to the exclusion of other foods. Too much of either Daphnia or brine shrimp, or both combined, can cause problems with many varieties of fish. These food animals are protected by a chitonous shell material that acts the same in fish as roughage does in a humans. It can have beneficial laxative effects in moderation, but can cause intestinal blockage in excess.