Feeding Larval Fish and Shrimp
Tech Talk 19
Larval fish and shrimp are plankton feeders. They feed on algae and/or animals of a size they can eat in one bite. In nature, they may live in a plankton soup, from which they can select what they want to eat. There will also be other things choosing to eat them.
In aquaculture, this process must be controlled in order to achieve a consistently high survival rate at an acceptable cost. Larval culture in ponds controls the process by timing: fill a dry pond then add fertilizer a few days before stocking with just-hatched larvae. The naturally occurring plankton algae and the zooplankton that appear shortly thereafter are at just right the stage for the growing larva but too small for larger predators.
Indoors, Artemia and rotifers, which are fairly easy to raise, are used as carriers for delivering algae and enrichments to larval fish and shrimp. The algae can be fed or soaked in a HUFA emulsion for a few hours before feeding to the larva.
Artemia older than 24 hours and rotifers have very little nutritional value. It is essential to enrich them with algae or dried diets immediately before feeding to the larva. Using live algae in the culture tank (green water culture) has the added benefit of improving water quality by removing ammonia and other metabolic by-products of the larva. Algae paste can also be used as an enrichment; however, it does not remove ammonia as the live algae does. Emulsified, dried diets can also be used, but they should not be added directly to the larval rearing tank, as they can foul the water.
If you choose to use the freshly hatched Artemia, which have some nutritional value, it is important to decapsulate the cysts prior to hatching them. Decapsulation is a process of removing the outer shell of the Artemia cyst. This is done so that the larva does not ingest the shells, which can cause obstruction and death. The outer shells are also a common source for bacterial infections. Decapsulation (See Tech Talk 100 for more info) is usually done by hydrating the cysts and soaking them in a hypochlorite solution until the shell is dissolved. Reference the Plankton Culture Manual (WBQ32) for a complete description of this process.