Feeding recently hatched larval fishes

Recently hatched larvae of most egg layers are too small to eat even the finest dried prepared foods available. As soon as their yolk sacs are used up they are ready to feed. The larvae require live tiny animals collectively termed infusoria. Recently hatched Cichlids are generally to large to eat infusoria as are most livebearers. After several days of consuming infusoria most larvae will have doubled their lengths and may be large enough to consume nauplii larvae of brine shrimp and then finely ground dried food.

Infusoria or green water- to the fish-breeder the word "Infusoria" means almost any aquatic animal that is of a suitable size to feed young fishes before they are large enough to consume brine shrimp nauplii or small Daphnia. Rotifers also are generally included as part of Infusoria. Many of the rotifers live attached to Daphnia. Infusoria includes protistans such as Paramecium and Euglena. Averaging in size something like small dust, a fine-meshed net such as as plankton net is needed to catch them. The spring, summer and early fall are the best times to capture infusoria from productive ponds and lakes. Care should be taken to avoid introducing unwanted pests or predators. Well-established aquariums contain infusoria, but not in sufficient densities to feed hundreds of tiny fish larvae. A separate rich supply is needed. The illustration below shows two microscopic protistans: a Euglena and Paramecium (magnified at about 500 X). Next in the top row is a rotifer which feeds on the protistans, algae and detritus. Rotifers can be viewed with a low power microscope or a high power dissecting scope. On the right side of the top row is a zooplankter called a water flea or Daphnia (note the rotifers on its back). Zooplankton are just visible to the naked eye but can be viewed with a high power dissecting scope. The second row shows more zooplankton: two Clodocerans like Daphnia, a copepod (Cyclops) and a copepod nauplii larvae.

Cultivation of Infusoria-one method to culture infusoria is to set up a mild decomposition in water. If you start with water from an existing aquaria or pond the culture will be produced more quickly. Seasoned tap water will also work. A gallon of water and a handful or so of organic materials will suffice. Organics can include crumpled lettuce, chopped hay, rice, a banana peel or even grass clippings. Cultures depending upon decay should be started every few days in order to keep a supply of infusoria constant. Aeration freshens these cultures and direct sunlight will promote an algal bloom which will probably translate into more protistans per unit volume of water. Alternatively, banana peel, hay and a few drops of milk are placed in a jar of seasoned water which is then left for a week. A few drops of milk are added each day. At the end of one week the banana peel and hay are removed. The culture should continue to produce micro-oganisms.

Laboratory type methods are also available to produce colonies of selected infusoria, usually Paramecium. A boiled (20 minutes), cooled and strained culture medium is inoculated with selected organisms. Biological laboratories sell pure starter cultures. Only small quantities of the starter culture is needed. Rice, chopped hay, canned pea or black bean soup, dried lettuce leaves are among the suitable stocks for boiling. Use about three tablespoons of mixed ingredients to a quart of water. This may be kept covered as stock and further diluted with water when poured into culture vessels for inoculating. Another method is to used dried skim milk as a culture medium. About two pinches to a pint of boiled and cooled water. The milk and seed micro-organisms should be placed into the water at the same time. A rich growth takes about four days. A pinch of dried milk should be added every three or four days to keep the culture going. Commercial tablets are also available to simplify the process of infusoria culture. Most of the methods described produce unpleasant odors and should never be kept in domestic food preparation areas.

Feeding your fish larvae- the best way is to use a fine plankton net to filter out infusoria from your culture and add them to your larvae tank. You would not want to add the culture media (described under laboratory methods) above to your larvae tank. If you produced a more general culture as first described you could remove a cup or so and add it to you larval tank. Add a cup of seasoned water back to the culture as make-up water. For the first couple weeks of larval growth, a 5 or 10 gallon tanks is large enough. If you use too large a tank, the infusoria you add would be highly diluted upon addition to the larval tank.

Brine shrimp - (Artemia salina) larvae or nauplii are a excellent food for larval fish which have outgrown infusoria but are not ready for finely ground dried food. Dried eggs of Artemia can be stored for years. The dried eggs are placed in a saline solution (20 g /liter = 20 ppt or about 1 tsp seasalt to 1/4th gallon) which is gently aerated. Hatching takes place in two to three days at room temperature. The nauplii can be filtered or removed with an eye dropper or pipette. They are attracted to light. Care should be taken not to introduce the spent egg shells into the tank with fish larvae. The illustrations below show the nauplii, metanauplii and two adults.