Various floating cage and fishpen designs are employed to meet enclosure requirements of shrimp and milkfish brood-stock, and for rearing of other finfish at the lgang Substation of the SEAFDEC Aquaculture Department in Nueva Valencia, Guimaras Island. In addition, support facilities are constructed like pontoon catwalks, wet laboratory, pumphouse, power house and researchers' quarters. With the establishment of the Department's Naujan Substation in Mindoro in 1978, floating cages and transport cages are also designed and installed. Following encouraging results of milkfish broodstock studies leading to natural spawning, rematuration and re-occurrence of natural spawning and completion of the milkfish life cycle, a development plan for the lgang Substation was prepared for full development of the Substation as a mariculture center. Specific recommendations towards this end are presented.

A pilot project for the pen culture of Tilapia nilotica and bighead carp in an irrigation canal was initiated in Barangay Cauayan, Pototan, Iloilo. The project, Cauayan Social Laboratory, involves cooperators from the community and other government agencies with the aim of improving the quality of life of the rural poor while at the same time increasing fish production through aquaculture. Three barrier nets that contain the fish stock were set across the irrigation canal at 30 m distance to provide two culture areas. Six days after completion and stocking, however, despite all maintenance efforts, these structures collapsed due to heavy fouling — an environmental factor that was not foreseen. Giving due regard to this phenomenon, a modified design was constructed with provision for free passage of potential foulers and general flotsam that may be discharged in the irrigation canal. In addition, considerations were also given to maintenance work, especially the cleaning of fouled wire and mesh nettings used to enclose the cultured stock.

Ferrocement was first used in the Department in fabrication of broodstock and hatchery tanks for shrimp. In 1981, the Capital Outlay Project at Leganes called for the design and construction of 210 gates, consisting of 2 main gates, 111 secondary gates and 96 tertiary gates. Of the secondary gates, 97 were designed using ferrocement, with 30 and 67 of the sluice culvert type, respectively. Ferrocement gates were fabricated in panels at a central work station and assembled at site. Panel geometry was controlled such that it could be carried by two or three laborers. A standard mixture ratio of 1:2 (cement:sand) with minimum amount of water was used. Several reinforcing bars arrangement were used with a single layer of gauge No. 20 welded 12 mm × 12 mm wire mesh or chicken wire. Construction cost appears favorable with respect to reinforced concrete gates but costs more than an equivalent wooden gates. After 3–4 years the ferrocement gates appear to be still functional. The potential is great with more improvements to be undertaken.

Unicellular algae, particularly Chlorella, are widely used as starter feeds for marine finfish larvae. However, milk fish larvae when reared on Chlorella sp., suffered morality up to 100% within the first days of feeding (Fig. 1). Morality induced by Chlorella occurred earlier than that induced by starvation. The present Communication describes histopathological changes in liver and intestines of mlikfish larvae fed with Chlorella sp., copared with starvedor Artemia-fed fish. Feeding the larvea with Artemia for 7 days evofed (Ø 12-16 micro m) hepatocytes, with a well-developed and orderly arranged rough endoplasmic reticulum (rER). Greater amounts of glycogen were deposited. Whereas those fed with Chlorella (Fig. 2) resulted in cellular shrinkage (Ø 5-7micro m), complete absence of stored products, degeneration of rER. swelling of mitochondria and augmentation of lysosome-like structures (compare also Juario & Storch 1984). Starvation-related alterations of hepatocyte ultrastructure were essentially similar. The intestinal tract of milkfish larvae is subdivided into pharynx, esophagus, stomach, intestines I(making up to 70% of gut length), II(up to 20%), and III (up to 10%). Nutritional related changes were only observed in intestines I and II. In Artemia-fed specimens there was intensive lipid absorption in I (Fig. 3) and well-developed supranuclear vacuoles in II (Fig. 4). Under starvation, The first part of the intestine was characterized by partial cellular hydrops, autolyic vacuoles (Fig. 5) and a dissolution of basal labyrinth. The supranuclear vacuoles of II were reduced to smaller, electron dense inclusions (Fig. 6). Chlorells appeared partially digested in the gut. It evoked pathological intrcellular vacuolation of the epithelial cells and bizarre forms of the nuclei in I (Fig. 7). In II, changes were similar to starved larvae (fig. 8). The present report is another example of high moralities occurring among fish larvae reared on live feeds (compare Eckmann 1985).

Milkfish culture is gradually shifting from the traditional extensive aquaculture system, where in the fish depends mainly on natural food for growth, to semi=intensive or intensive culture systems in which additional inputs such as formulated diets are used to increase fish production (Chen, 1981). This paper reviews present information on digestive organs and enzymes, food and feeding habits of the age groups, digestibility of feedstuffs, and nutrient requirements for milkfish.

Penaeus monodon juveniles were reared in 60-liter fiberglass oval tanks in a flow-through seawater system for 8 weeks to determine the effect of lecithin and type of lipid on growth and survival. Nine isonitrogenous and isocaloric diets consisting of a basal practical diet (40% protein, 10% lipid) with 3 levels of soy lecithin and 3 sources of lipid cod liver oil, crude degummed soybean oil and purified soybean oil were used. Feed was offered twice daily. Percentage weight gains significantly increased as the level of lecithin was increased from 0 to 2% regardless of the lipid source. At all levels of lecithin, survival rates were significantly higher in those fed diets containing crude degummed soybean oil compared to those fed either cod liver oil or purified soybean oil. Lecithin levels and lipid sources did not significantly affect the feed conversion values. The best was that which had 2% soy lecithin with 3.8% crude degummed soybean oil.

An experiment on the integrated farming of broiler chickens with milkfish (Chanos chanos), tilapia (Oreochromis niloticus) and shrimp (Penaeus indicus) in brackishwater ponds was conducted in 1,000-m² ponds of the SEAFDEC Research Station at Leganes, Iloilo, Philippines. Tested were varying densities of tilapia (500, 1,000, 1,500 and 2,000 for Treatments I-IV, respectively) with fixed densities of 5,000 shrimp and 200 milkfish per 1,000-m² pond. Poultry houses were constructed at the middle of each pond so that fresh chicken wastes would drop directly to the pond. Each unit was stocked with 90 broiler heads of three size groups, or a total of 180 heads for 120 pond culture days. Stocking, transfer and harvest of poultry were done every two weeks. Results indicated an average net production of shrimp of 19.15 to 28.38 kg/1,000 m²; milkfish, 7.51 to 11.74 kg/1,000 m²; tilapia, 33.68 to 66.97 kg/1,000 m² and chicken broilers, 180.90 to 217.39 kg/1,000 m². Statistical analysis revealed that the best net production of tilapia was obtained at a stocking density of 15,000/ha.

Natural spawnings of milkfish from floating cages were obtained from different stocks of 5-7 year-old milkfish in 1980, 1981, 1983 and 1985. The maximum number of eggs collected in 1980, using a series of 1-m diameter stationary plankton nets, was about 900. Increased collections were obtained in succeeding years with different types of egg collectors and methods. Egg collection, however, is inferior when based on the expected number of eggs spawned by a single female. Although no systematic study was attempted to compare efficiency of various egg-collecting gears and methods, the problems associated with the use of each gear are presented. The experience may be used as a guide in future designs of efficient gears of collecting naturally-spawned eggs of milkfish or other fish species in floating cages.

The development of a shrimp (Penaeus monodon) production system integrated with livestock was undertaken at the Sycip Plantation Inc., Negros Oriental, Philippines, as a result of crop diversification efforts in the province. Heavy organic manuring of brackishwater shrimp ponds strongly stimulated the production of lablab in the initial stages of pond preparation. Observations suggest that the problem of deteriorating water quality in the later stage of culture due to prawn burrowing/feeding activities, was exacerbated by constant addition of manures. Plankton analysis of pond water indicated that this was a result of excessive nanno- and picoplankton blooms. A highly significant correlation (P < .001) between plankton (cell size < 5 microns) count and BOD was obtained. An alternative system using "kitchen ponds" stocked with artemia provided a suitable source of food for shrimp growth. Daily additions of manure (100 kg dry weight/ha/day) produced an average 40 kg of mixed artemia and lablab protein each day during a three-month study period. Analysis of input:output ratios for the kitchen pond showed a net loss in organic matter and net gain in nitrogen yields during the conditioning period. Conditioned ponds had a net gain in both organic matter and nitrogen yields. An area ratio of 1:5 for kitchen pond to shrimp grow-out enabled production at 700-1,000 kg/ha/crop at 30,000 pieces/ha stocking density, 60-70% survival and grow-out period of 120 days. Significant reductions in feeding costs were obtained.

Milkfish,Chanos chanos fingerlings transported by boat (petuya) for seven to eight hours were observed for stress-inducing factors during transport, daily for 10 days after stocking in pens in Laguna Lake, Philippines. Handling, hauling, and crowding of fish contributed to stressful conditions. Likewise, the transport procedure of the clising the water entry hole at the bottom of the boat to block water exchange was associated with decreased dissolved oxygen and increase tubidity, with respective values of 2.4 mg/l and 79 Formalin Turbidity Units when water change was possible. In addition , marked and abrupy fluctuations in salinity from 15 to 30 ppt then 0 ppt within 1 to 3 hr were observed during transport. Although moralities during transport were minimal, subseqeunt deaths after stocking in pens mounted to not less than 2.4%. Reddish snout, scale loss and hemorrhagic areas along the lateral body surface wwere observed. Bacterial counts of water increased significantly during trasnport when water exchange was stopped. Kidney and skin/muscle specimens yielded significantly higher bacterial counts on days 2, 3, 5 and 8 poststocking predominated by Aeromonas hydrophila biovar hydrophila and two species of gram-negative bacilli phenotypically resembling Pseudomonas sp.