15 DECEMBER 1999

J.M. Estrada

The cultivation and use of live feeds is one of the principal limitations for large scale larval rearing of fish and crustaceans. A good diet should be the right size, have the correct nutritional content and be appetizing for the larvae. Traditional diets made up of rotifers and Artemia, are not always of optimal nutritional quality The shortage of Artemia cysts is also a problem that has intensified in recent years.

To resolve these problems, alternative diets that provide adequate nutritional requirements, were needed. A first option was the collection and use of natural zooplankton as diet for marine fish and crustaceans larvae. This technique relies upon the natural variation in concentration and composition of zooplankton and also carries the risk of disease contamination, making it incompatible with commercial larval production.

The next option was copepod cultivation, which is the main diet of marine fish larvae. The commercial culture of copepods was developed by Maximus Inc. (Denmark) and applied successfully in the industrial culture of turbot larvae in 1995. Fundacion Chile was, at the same time looking for alternatives in the production process for intensive green water systems used with turbot culture, to improve the survival and pigmentation levels. As a result of this search, the project FONDEF D96-1068, from 1997 to 1999, developed a semi-intensive culture method for turbot larvae, using copepods and this technology was then tested in the Eastern Pacific. In 1997, a culture facility using this technology was built in the country's 5th Region

This cultivation method is based on the ecological balance of the following components: Primary producers (microalgae), primary consumers (copepods), secundary consumers (fish larvae) and decomposers or recyclers (bacteria). To keep this system under control, strict monitoring of the productivity levels of each component is necessary, as well as the physico-chemical variables that have an important influence on productivity.

The facilities needed for copepod culture are:

• area for copepod cultivation: round tanks of 20-30m diameter and 3m depth. The tanks are semi-buried and uncovered.

• filtration area: used for the filtration of the incoming water as well as for concentrating copepods and nauplii coming from the cultivation area and going to the larval rearing.

• larval rearing area: round tanks 5-10m in diameter and 3m depth, they are burried and kept under a greenhouse environment.

After building the facilities, the process of collecting copepod specimens from the natural environment began. These samples were grown in a controlled environment for three generations, before using them in fish larval rearing. Only wild copepods were collected at this time, and all the tests were carried out using exclusively cultivated copepods.

After a year's operation, this technique of copepod cultivation on a large scale was mastered and adjustments at production level could be made to meet the larval rearing requirements. Several tests were carried out, obtaining an average survival of 10% and 100% pigmentation.

As a result of using this new system, a reduction on the following items was possible:

• costs associated with the production of live feeds

• the percentage of deformities and bad pigmentation

• 5% reduction in the original weaning period

• need for covered space, optimizing the hatchery's productivity

• labor costs associated with larvae feeding

• dependency on scarce diets like Artemia

• need for antibiotics use

(Fundacion Chile)

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