5 Production of farm-made larval feeds

MANY DIFFERENT farm-made feeds can be used in the rearing of freshwater prawn lar vae, in addition to the feeding of brine shrimp nauplii (BSN). This annex describes the preparation of three versions of an egg custard diet (EC) and the use of fish flesh. The first EC diet is an egg-mussel mixture. Experience has shown that using fish flesh (larval diet No. 4), especially when carelessly prepared or overfed, can be a grave source of water pol lution in larval rearing. Farm-made larval diets No. 1 and No. 3 are the most simple to prepare.

Farm-made larval diet No. 1:
Prepare as follows:
blend 0.5 kg of shelled mussel (other molluscs can be used, but mussel seems best) in a blender;
strain the chopped mussel through a coarse cloth and discard the connective tissue, retaining only the material which passes the strainer;
using the whole of the mussel which has passed the strainer, add three or four whole eggs and stir thoroughly in the blender (note: it is important to use the white as well as the yolk of the egg - the white contains good quality protein - some people think using the white of the eggs causes water pollution but it does not if homogenized properly);
steam the mixture over water (like poaching an egg) until it solidifies into a custard; screen to the correct size (see the main text of the manual) and feed directly; or you can refrigerate it for a few days for later use (however, the quality of frozen EC is not as good as fresh EC for feeding purposes).

Farm-made larval diet Nos. 2 and 3
Prepare as in larval diet No. 1 but use the ingredients shown in Annex 5, Table 1.
Farm-made larval diet No. 4
Skipjack tuna, bonito or mackerel are good types of fish to use when preparing this feed. It may also be used as an ingredient in larval diet No. 1 above, partially or totally replacing mussel. The results with mussel seem to be superior.
Prepare the fish as follows:
fillet the fish, discarding head, bones and viscera;
grind and liquidize the flesh, as for the mussel in larval diet No. 1, in a blender; force the flesh through stainless steel sieves with a strong jet of freshwater (this grades the particles and washes the flesh free of blood and excess oil). The mesh sizes should be chosen to produce particles of a size relevant to the age of the prawn larvae (see the main text of the manual);
use the fish flesh directly; or form into balls of known weight for storage (it may be kept in the refrigerator for 2- 3 days or frozen for longer periods; however, frozen material is less satisfactory than fresh).

TABLE 1 ANNEX 5
Ingredients for farm-made larval diets Nos. 2 and 3

NOTE: TETRACYCLINE HAS BEEN USED IN LARVAL DIET NO. 2; YOU SHOULD READ THE TEXT OF THE MANUAL CONCERNING THE DANGERS OF REGULARLY USING ANTIBIOTICS IN HATCHERIES.

INGREDIENTS QUANTITY OF INGREDIENTS LARVAL DIET NO. 2 LARVAL DIET NO. 3

SOURCE: DERIVED FROM LAVENS, THONGROD AND SORGELOOS (2000)