2. FORMULATION AND PREPARATION OF FEEDS FOR MILKFISH AND SHRIMP CULTURE USING LOCALLY AVAILABLE MATERIALS

Intensive culture of milkfish depends on the growth of natural foods as a major source of nutrients. When underproduction or overharvesting of these occurs, supplemental foods such as rice bran, broken pieces of soybean cake, copra, peanut cake or various leaves and seeds are often provided. The efficiency of using artifical foods is increased by their preparation in uniform particle sizes which are acceptable to fish. Compression and extrusion of food mixtures into pellet form, provides even greater efficiency, minimizes sorting of ingredients and concentrates the nutrients into a small volume. This kind of food preparation is widely used for fish that will accept pellets.

Research into the formulation and processing artificial foods as single ingredients and as pelleted mixtures for milkfish and shrimp was already underway at the Station. Pellets were made by selecting several dry ingredients which made a soft dough when mixed with water. This was then squeezed into ribbons through the holes in the plate of a “food chopper” or small home grinder. Formulas prepared in this manner and sun dried, that contained about 30 percent water with three to five percent tapioca (cassava starch) held together when immersed in water and smelled “sweet”. Typical formulas are shown in Table 1.

Formulation and processing for acceptance by fish and several extruded formulas were made up with surplus local ingredients (See Appendix 1), sun-dried and fed to milkfish stocked in plastic pools.

Examples of these formulas are shown in Table 2.

¹ The residue from pressing ground, cooked soybeans to recover a cake sold under the name “Tahu.”

These pellets retained their original shape for as long as four hours in water, yet within a few minutes softened and easily broke down into individual components when touched. Although the fish did not appear to eat these pieces, examination of intestinal contents of several fish revealed cassava and rice bran from the pellets. It was estimated that the entire gastro-intestinal tract was 10 percent filled with feed and detritus.

Because the reaction of the milkfish to these pelleted feeds was disappointing, the gastro-intestinal contents of fish stocked in tambaks were compared with the natural foods which were ingested. We attempted to duplicate the decaying algae which supplied most of the milkfish diet with a mixture of ground and sifted vegetable products, formed into a soft mass by steaming with cassava as a binder. A typical early experimental formula is shown in Table 3.

This formula was made by hand into flat, 60 to 70 gram cakes, steamed for 15, 30 or 45 minutes and fed to milkfish. After observing the cakes by swimming to and fro for a short time, the fish, following a leader, passed directly over them. On the next pass they delayed to nibble and soon each fish appeared to be bumping the cakes with its mouth, pushing them slowly in a complete circle around the pool sides.

By placing cakes in shallow bamboo trays of 0.5 metres diameter for fish stocked in plastic pools, and in open wooden boxes for fish stocked in a 0.2 ha tambak, it was possible to observe the degree of feed acceptance and recovery of particles. During the next month forty five different formulas were made and tested and it was possible to propose guidelines for a “home industry” method of fish feed preparation.

To make fish cakes containing ten percent protein (wet) or 18 to 20 percent (dry), that are competitive in cost with poultry foods and acceptable to fish, the following procedures are recommended:

1. Use from 40 to 48 percent water, depending on the amount of cassava, the time of steaming and bulk density of the mixture.

2. If 35 to 40 percent fresh cassava is used, it forms a sticky, water-resistant cake, binding the other ingredients until eaten by fish. When the cassava is dry, use 14 to 16 percent and add extra water to the formula.

3. Bulky ingredients (rice bran, coconut cake, etc.) should not exceed 40 percent. (Note: this will not apply to a feed compressed into pellets by a commercial pellet mill.)

4. Use 20 percent dried and ground leaves such as Mlandingan, Turi and Cassava. Wet leaves may be used if the formula is adjusted for water content.

5. For small milkfish use kapok seed in the cakes only if they are ground and sifted to remove the hard coating. Hand-ground rice bran made by “hullers” must be sifted to remove the hulls. (Note: cakes containing 12 percent sifted ground kapok seeds were eaten readily.)

6. Use small slipmouths and anchovies as an ingredient in feed cakes. They seem to be a lure, are easily ground, and are often available at low cost during surplus harvests or when slightly spoiled and unsuited for human consumption.

A final formula was made on 30 December 1974, which proved very acceptable to fish and passed all other tests for a feed cake; it was firm after steaming, sank in the water, and held together for four hours, allowing fish to locate and pick it apart, as shown in Table 4.

Without changing its texture, this formula may be modified to include more protein from soybean meal, peanut cake, green peas, animal blood, fresh fish, or high-protein leaves. The amount of rice bran and soybean cake waste can be adjusted to these high-protein sources. Vitamin premix must be added for all feeds used in plastic pools, but in ponds containing some natural foods this may not be necessary. The vitamin levels that appeared adequate for milkfish confined for two months in plastic pools was 20 gms/kg/feed of a premix designed for fortifying poultry rations. It can be purchased from the Poultry Shop in Semarang.