Daphnia
By: Roger Winter

Some live foods are impossible to cultivate all year round indoors and for those of us who live in temperate climates we must cultivate these outdoors during the warmer summer months. With the summer weather still with us perhaps now is the time to look at one of the best known live foods we give our fish, Daphnia. Also commonly known as water fleas because of their similarity in shape to a flea and their method of swimming through the water with a jerky motion they are in fact a crustacean and have no relation to a flea in taxonomy or lifestyle.

We have already covered the year round culture of Daphnia's smaller cousin Moina and as life cycle of both Moina and daphnia are the same I refer you to the Moina article  for information on breeding method and life cycle of Daphnia. They occur naturally in most bodies of water but rarely in large enough concentrations to harvest easily and those aquarists who know of such a site are loath to share the information. For a large concentration to occur two things are necessary, a lack of predators and decomposing organic matter to provide their food. Such conditions are most often found in duckponds in public parks and farmyards and in standing water in which domestic rubbish has been dumped. The ideal conditions are alkaline or neutral standing water with a temperature of between 65o - 75oF with a total lack or few predators,such as fish, and the presence of decomposing organic material. As few of us have access to such a site then these are the conditions we need to reproduce to breed and harvest the fleas.

A starter culture of Daphnia can either be caught from the wild or by using one of the bags of live Daphnia sold in most Tropical fish shops throughout the year. Once a culture has been productive it will restart again when the conditions are suitable even if frozen solid throughout the winter.

Shallow containers of not more than 12 inches in depth (30mm) seem to work best, whilst the Daphnia do survive and breed in deeper containers they never seem to reach the populations achieved in the shallower ones. This may of course not be true for containers with a large surface area but as all my cultivation is done in small washing up type bowls about 12inches square with great success whilst attempts using water butts failed this is the method I will describe. The container should be thoroughly cleaned and filled with alkaline water, my local tap water (liquid rock) is very suitable and I use it straight from the tap but if your local water is soft or acid it must be treated by adjusting the pH, a piece of Tufa rock may also help. It should be sited so that it receives plenty of light including some direct sunlight but do avoid placing were it receives direct sunlight all day. If this is the only position available then shade part of the container with a piece of wood or similar. Now add the fleas. It is the feeding of the fleas were most mistakes are made as it is very easy to pollute such a small body of water. Various substances are recommended as food such as rotting lettuce, sheep manure, green water and yeast. Whilst all these work, some better than others, care must be taken not to introduce to much organic matter as the water will foul and the fleas die from lack of oxygen. If mulm is present on the bottom of the container then the eggs laid by the fleas as conditions worsened will hatch as the fouling is cleared by bacterial action but as fouling may occur very quickly is small containers they may not have time to lay any and in either case harvesting of the fleas is delayed. I find the best food is Gram flour (obtainable from any Indian food shop ) which is made from chick peas. A tablespoon of the flour is mixed into a smooth paste with a little water then made up to a pint (1/2 litre) with water and stirred well. This cloudy mixture is added to the cultures until the water in the culture is slightly cloudy but the bottom of the container can still be seen. Any excess mixture can be stored and used as required. Normally within a few days the container will contain a cloud of fleas, some of which can netted out and fed to your charges. If the water has cleared add a little more of the Gram flour solution. Once producing fleas can be harvested every day with little effect on reducing the numbers present in the culture, in fact regular harvesting seems to encourage the constant production of large quantities of Daphnia within the culture. As in its natural surroundings the culture will eventually pulse and the number of fleas present be minimal. Do not worry when this happens just feed very sparingly and observe the culture, within a short time the culture will experience a population explosion again and harvesting can restart. Even one bowl can provide enough fleas for several tanks on a daily basis but as with all cultures it is best to maintain several as apart from the increased harvest you always have the means to start a new culture if one of the established cultures suffers a disaster. Daphnia do not like any higher forms of plant life in the water with them and any growing plant, including thread algae, in the container will have a detrimental effect on production. If any containers do become contaminated with algae net out the remaining fleas and use to start a fresh culture in a clean container and scrub out the old one before reusing. Daphnia like all crustaceans is covered in a hard chitenaous shell which has little food value except as roughage and some literature implies that fish fed exclusively on Daphnia may suffer digestive problems. Whilst I do not feed my fish solely on Daphnia I know of several aquarists who feed Daphnia almost exclusively with no problems. In fact at the times when I have had an excess of fleas the fish seem to eat their fill and any excess is left to swim unmolested in the tank for several days. Many aquarists prefer the red Daphnia as they feel it is more nutritional than the other types. Whilst this may be true the colouration. of Daphnia is partially dictated by the food they are consuming, green Daphnia are eating mainly single celled algae the red is caused by the presence of haemoglobin in the blood of the animal. The less oxygen present in the water then the more haemoglobin will be present in the fleas blood to extract the oxygen, as haemoglobin is a protein then it is most probable that the red coloured fleas present in poorly oxygenated water are more nutritious. Red colouration. can also be caused by carotene or other substances present in the water as well and as the fleas are eaten whatever the colour why worry. One point though is that Daphnia require oxygen in the water the same as fish and if you overfeed you fish with Daphnia so that not most if not all are consumed then they are competing with the fish for oxygen, a fact that may explain dead fish in tanks with large quantities of Daphnia that have given rise to myths of fish dying from overfeeding on fleas.

Obtaining starter cultures.

In most articles I will give directions for obtaining starter cultures, so far the articles have covered the various worms, white, grindal, mico and vinegar eels and fruit flies. Starter cultures of these can all be obtained from aquarists maintaining them. Most killie keepers and a growing number of livebearer keepers maintain livefood cultures as do aquarists who do a lot of breeding, also some avid showmen are realising the benefits of culturing their own livefood. A good place to enquire first is at your local aquarist society were one or more of the members may be able to help you. Small ads in the back of the various aquatic publications are often placed by people specialising in the supply of live food cultures and if all else fails then look in your yellow pages for Biological supply houses who may be able to supply you with what you want or point you in the right direction.

With Permission from
Viviparous