The nutritional quality of nematodes ( Microworm ) can be enhanced by the use of the bio-encapsulation technique

Nematodes 

The use of the free living nematode, Panagrellus redivivus ( Common name : Microworm ) as larval food has been demonstrated successfully for several species, including Crangon crangon, juvenile king shrimp (Penaeus blebejus), common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix). 

P. redivivus is a suitable larval live food since it is small (50 µm in diameter). Moreover, it has an amino acid profile that matches that of Artemia (Table 6.2.), while its EPA and DHA content is respectively nearly a third and almost the same or a little higher of that of Artemia, (Table 6.3.). P. redivivus can be cultured very simply in trays filled with 70 g of flour (10.8% protein) per 100 cm2 , the latter kept humid by spraying with water. The culture medium is supplemented weekly with 0.5 g baker’s yeast per 100 cm2 , which should inhibit the growth of nematophage fungi. The containers should be stored in a well ventilated room at a temperature of 20-23°C. Contamination by insects can be prevented by covering the containers with cloth. The nematodes are harvested daily for about 53 days using the same culture medium by removal from the substrate with a spatula (Fig. 6.2.). A maximum daily production of 75-100 mg per 100 cm2 is reached at week 3. For smaller cultures the nematodes can be harvested by adding a small quantity of distilled water to the trays and decanting the suspended nematodes. The nematodes have a short generation time ranging from 5-7 days and a high fecundity. 290 Table 6.2. Comparison between the protein and amino acid compos

The nutritional quality of nematodes can be enhanced by the use of the bio-encapsulation technique. Enrichment is simply carried out by adding the product to the culture medium (direct enrichment) or by bringing the nematodes in an emulsion of the product (indirect enrichment). Rouse et al. (1992) used for the direct enrichment a culture medium which was fortified with a 10% fish oil emulsion, obtaining nematodes that had a significantly higher total lipid content and elevated levels of (n-3) HUFA (i.e. 11.2% and 4.8% respectively; Table 6.3.).

The bioencapsulation technique can also be used to fortify the nematodes with therapeutics (bio-medication). For example, nematodes can be placed in 1 l beakers with 500 ml of fresh artificial seawater and 5 g of Romet-30 premix (Hoffman - La Roche, Switzerland) containing 25 % sulfadimethoxine, 5 % ormetoprim and 70 % rice bran carrier. After a 4 h boost period, during which the nematodes have accumulated 0.25 µg of the drug per individual (0.1 µg.ind.-1 for Artemia nauplii), the nematodes are separated from the antibiotic carrier by resuspension in seawater and centrifugation at 1500 rpm for 10 min. After a 10-20 min period the animals have migrated to the top of the tube, where they can be collected with the use of a pipet onto a 100 µm mesh screen. After rinsing with seawater, the nematodes can then be fed to the larval predators.

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