Live food
Milkfish larvae are reared on Brachionus, Moina, and Artemia. Rotifers and Artemia are normally enriched with DHA (Protein Selco. INVE Aquaculture, Dendermonde, Belgium) (Gapasin and Duray, 2001). To reduce the dependence on live food in the hatchery, artificial microbound larval diets have been developed (Borlongan et al., 2000).
Supplemental Feed
In ponds supplemental feed is provided when natural productivity of the water cannot sustain optimum fish growth. Supplemental feeds can be in the form of a single feed ingredient (e.g., rice bran, reject snack foods), two mixed ingredients, or formulated low protein diets (Table 3). Protein sources like local fish meal is usually mixed with rice bran and either pelletized or not, while snail meat and entrails of fish or chicken are blanched, chopped, and fed directly to the fish. The estimated apparent FCR for these feedstuffs/feeds is about 4 to 5:1. Plant sources rich in carbohydrates such as rice bran, boiled corn, bread crumbs, and Azolla are fed as a single feed or mixed with other ingredients, pelletized and dried. Leaf meals like cassava, swamp cabbage, and sweet potato in combination with other ingredients are also used as supplemental feed. Rice bran as a single ingredient is often fed to milkfish in semi-intensive pond culture (at a stocking density of 8000 fish/ha) with an apparent FCR of about 3.9:1.
Formulated feed
Fish farmers prepare farm-made feeds (either as single or mixed ingredients) or purchase commercial feeds. Farm-made feeds are usually fed in dry form and prepared by mixing, pelletizing, and air drying. Moist feeds are not commonly used for milkfish. Dry, farm-made feeds are easy to prepare, store, and transport, and relatively cheap (depending on the availability of ingredients used). However, these feeds are unbalanced and result in low production levels (Table 4). Formulated milkfish feeds are available as sinking or floating pellets. Extruded, floating pellets are more expensive than sinking pellets but allow for easy monitoring of feed consumption. Feeding trays are normally installed in cages and ponds to reduce wastage.
Table 5 lists the feed ingredients that are used, or have the potential to be used, as protein and/or energy sources in milkfish feeds. The major feedstuffs used as protein sources are fishmeal, shrimp meal, meat and bone meal, and copra meal; soybean meal and other pulses are used both as protein and energy sources. Cereal grains and cereal by-products (rice bran, corn meal, corn germ meal, corn starch, wheat pollard, wheat flour) are used as energy sources. Other potential protein sources are snail meat, poultry by-product and feather meal, blood meal, cow pea, feed pea, and leaf meals (e.g. cassava leaves, swamp cabbage, sweet potato). Leaf meals can partially replace fishmeal in complete diets of milkfish (Borlongan and Coloso, 1994). Feed pea (Pisum sativum) can be used to replace 20 percent of dietary protein in milkfish diets containing 30 percent crude protein (Borlongan et al., 2003).
Examples of feed formulations and their proximate composition are shown in Table 6. Protein levels in formulated milkfish diets range from 46 percent for larvae, to 21–36 percent for grow-out in semi-intensive and intensive systems, and 36 percent for broodstock (Table 7 and 8). The main components of larval feed are fish meal, soybean meal, and shrimp meal. Broodstock fish are fed complete, high quality diets to assure high egg quality and larval survival (Emata et al., 2000).
Table 8 shows some examples of commonly used commercial milkfish feeds in the Philippines. Feeds are available in mash form for fry, crumbles for small juveniles, and pellets for later stages and are normally classified as pre-starter, starter, grower or juvenile, and finisher or adult diets. Commonly used binders for fish feeds in the Philippines are shown in Table 9. Preservatives such as butylated hydroxytolouene are used to prevent or delay rancidity of fats and deterioration of vitamins. Attractants and colourants are not popular feed additives for milkfish feeds. Vitamin and mineral pre-mixes are incorporated into the feeds, especially in complete diet formulation or feeds formulated for intensive systems. Examples of vitamin and mineral pre-mixes are shown in Table 10 and 11.
