3. BIOLOGICAL DATA

3.1 MILKFISH IN PLASTIC POOLS

On 11 November, each of five plastic pools, 2.5 m² in area, were stocked with 20 milkfish fingerlings. The bottoms of these pools were covered with about 8 cm of sand and covered with 25 cm of seawater.

Five additional plastic pools, 0.625 m² in area, were filled with 8 cm of mud which had been allowed to dry for several days, then filled with 35 cm seawater and stocked with five milkfish fingerlings.

During November, the reaction of the fish to pellets and cakes was observed. As already described the fish would not accept sun-dried pellets made by mixing ingredients with water and extruding through a food grinder. When placed on the sand bottom of plastic pools, these pellets disintegrated after about 30 minutes. It was not until the first part of December that a soft feed in cake form was developed which remained stable in water for several hours and this was offered to the fish.

Growth of the fish was somewhat affected by stress from poor water quality. Although over-feeding was not apparent, incomplete digestion of the feed resulted in enriched water that became so turbid within a week that the fish could not be seen. During the last two weeks of feed testing, the water was completely drained and replaced every other day. The supply of air was often cut off by an overheated pump, and almost every morning fish were on the surface gulping air.

Since many different formulas were made, there was no record of growth results on any one specific food. Efforts were focussed instead on feed acceptance, feeding habits and pool management. Efficient utilization of feed was achieved by placing feed cakes on bamboo trays; this focused feeding activity to a small area of the pond.

Several fish were lost when changing water in the pools; four were removed as “pin-heads,” possibly those which never learned to accept artificial food; and several fish jumped out of the pools if the sides were moved violently.

Data on changes in length and weight of fish in all five larger plastic pools is shown in Table 5.

Table 5
GROWTH OF MILKFISH IN PLASTIC POOLS

Combined Data Date	No. fish				Av. length		Av. weight
11 November		100			131.1 mm				17.1 g
6   December		90			not measured				16.5 g
2   January		85			136.4 mm				20.8 g
Individual pool data
Pool No.
Date
11 November	131.3	17	129.8	17	131.6	17.25	131.7	17.5	131.2	17
2   January	134.9	19	134.0	21.25	136.1	21.1	136.9	20	140.2	22

3.2 MILKFISH IN TAMBAKS

According to available records, on 22 August tambak B-1 contained 385 milkfish. Their average weight was 66.6 grams. On 10 November, 100 larger fish weighing an average of 350 grams each were stocked followed by another lot on 18 December, 80 fish weighing 333 grams each.

Starting 2 December, feed cakes were placed in box trays anchored to the tambak bottom. All the formulas were readily eaten except one containing 20 percent kapok seeds. When this ingredient was sifted to remove seed hulls, the use of 20 percent in cakes was acceptable. However, examination of fish gastro-intestinal contents showed a high proportion of undigested kapok endosperm.

Tambak B-1 was used for testing food acceptance until 28 December, after which a single formula was used varying only in the amount of water and the use of dry or wet cassava.

Twenty-four fish sampled on 3 January showed an average weight of 390 grams and a length of 351 mm. Based on these figures, the condition factor (K = weight in kilograms divided by length in metres was 0.9. The “K” value for smaller fish at the end of tests in plastic pools was 0.95.

3.3 SHRIMP IN TANKS

During October, the captive Penaeus merquiensis spawned and several thousand larvae required food. Small lots of test feeds were made and used together with natural diatoms produced by fertilizing the water. Using common ingredients such as cockle, squid, fish liver and viscera meals, to supply amino acids, vitamins and trace minerals, several formula were prepared. The major requirements of feeds for shrimp larvae are: 1. acceptable particle size, colloidal at first, slightly larger particle later that will slowly sink and can be easily moved by air agitation; 2. particle integrity (will not dissolve or cause turbidity; 3) will produce growth and good conversion.

A formula which satisfied these requirements is as follows:

All ingredients were passed through a 210 micron sieve opening. The mixture was steamed to gel the cassava starch and provide the binding properties needed to prevent turbidity, and then sun-dried. For feeding small larvae, the mixture was washed through a 55 micron sieve, and for larger larvae it was passed dry through a 210 micron mesh.

Since other feeds were also used (Tahu, boiled eggs, cultured brine shrimp) and the water was fertilized to produce growth of diatoms, results of the formula feed alone were not determined.

Cakes: Three pools were stocked with 200 juvenile shrimp caught off the coast of Jepara. Fed nothing except milk fish feed cakes (formula similar to that in Table 2) for four weeks, the shrimp tripled their weight. Since no special effort was made to maintain water quality or to prevent cannibalism, this was considered only a preliminary test of feed acceptance.

Discussion of processing of fish feed cakes and equipment needed for home industry manufacture.

Tambaks are generally stocked twice yearly with 4 000 milkfish fingerlings per hectare, and are expected to produce at harvest 3 000 fish weighing an average of 0.33 kilograms. Peak feeding occurs near the end of the growth period when the calculated intake is approximately 30 kilograms.

Based on general formulations, slightly modified from Table 4, 30 kilograms of feed cake requires the following ingredients: