Interviews were conducted among eight Gracilaria growers in Panay, Western Visayas, Philippines from March to July (1990) using a structured questionnaire. The "rice planting" method was employed by farmers growing seaweeds in natural drainage canals and ponds. Initial harvests are made 15–60 days after planting. Higher production [ 7–14 t (dry) ha⁻¹ year⁻¹] are obtained from cultures in canals than in ponds [3–4 t (dry) ha⁻¹ year⁻¹]. The net income derived from culture in ponds is estimated at P698/crop or P6313/year (US$234/year). A higher net income of P4936/crop or P41766/year (US$1547/year) was generated from Gracilaria farming in canals. Returns on investment (ROI) from farming in ponds and canals are 39% and 908%, respectively. Payback period is 2 months in canal farming and 1.8 years in pond farming.

Rheological properties were measured for 1.5% agar gels from Gracilariopsis heteroclada pre-treated with powdered commercial lime (CaCO₃) during sun drying, and a combination of two alkaline solutions during water-bath heating in the laboratory. All samples were subjected to a one or three hours of heating prior to extraction. Slightly higher agar yield were obtained from samples treated with lime while drying (2.9-4.5%) than from seaweed (2.1-3.8%) treated with alkaline solutions in the laboratory. Better rheological (breaking strength,cohesiveness, breaking energy, and rigidity) and physical properties (dynamic gelling and melting temperatures) were obtained from laboratory treated seaweed after a 3-hour treatment. No effect of collection site, alkali treatment and treatment time on the yield of agar, was observed. However, significant (P ≤ 0.01) effects were recorded for collection site, alkali treatment and treatment time both on rheological properties and on gelling and melting temperatures.

Kappaphycus alvarezii var. tambalang was cultured in a 3 × 3 m bamboo raft installed inside a 4 × 4 m floating net cage of Lates calcarifer (sea bass) broodstock at SEAFDEC Sub-station Igang, Guimaras, Philippines, from December 1989 to May 1990. Growth and production of K. alvarezii var. tambalang was influenced by the culture months. The highest growth rate and production were recorded in January and May, respectively, while the lowest growth rate and production were observed in March. Average growth rate (wet weight) ranged from 3.72 to 7.17% day-1, while production ranged from 575.5 to 2377 g m-1 line-1. A total production of approximately 123 t (fresh) or 37 t (dried) ha-1 in the 5-month harvest season was produced from this culture system. Cultivation ofK. alvarezii var. tambalang in cages is possible, which indicates that seaweeds can be grown with carnivorous finfish, a practice which is still untapped.

The effects of streamer tags and initial prawn size on survival and growth in 2-month- and 7-month-old pond-reared juveniles of Penaeus monodon Fabricius (11-30 mm carapace length, CL) were assessed under laboratory conditions. Tagging did not cause immediate mortality in juveniles of 11-21 mm CL within a one-week period but led to a significantly lower survival rate after 6 to 8 weeks in 1-m³ tanks. However, tagged prawns of 21-30 mm CL showed high long-term survival rates up to 90% in a 12-m³ tank. The 2-month-old juveniles had lower survival rates than 7-month-old prawns. Specific growth rate was not affected by tagging but was significantly higher in smaller prawns. In general, there was no interaction between the effects of tagging and prawn size in terms of growth and survival rates. The lower long-term survival rate associated with tags may be due to the attractiveness of tags to predators, or to trauma or stress caused by the weight of the tags. These factors are discussed in relation to findings for other penaeid species.

Based on egg collection records, spontaneous spawning activity of sea bass, Lates calcarifer (Bloch), reared in floating net cages followed a semilunar cycle. The peak of multiple spawnings coincided with declining spring tides of quarter moon periods. Maximum diameter of intra-ovarian, ripe oocytes (0.51–0.55 mm) occurred in synchrony with the quarter moon periods. Smaller oocytes (0.44–0.47 mm) were sampled during the new and full moon periods. Two structural analogues of luteinizing hormone-releasing hormone (LHRHa) (des-Gly¹⁰, D-Ala⁶-LHRH ethylamide and D-Ala⁶, Pro⁹-Nethylamide-LHRH), in pelleted or dissolved form, induced mature female sea bass with a mean egg diameter of at least 0.40 mm to spawn at any day during the lunar cycle. The onset of spontaneous and LHRHa-induced spawnings occurred during low tides in the evening until dawn (from 19.00 to 05.00 hours). These results demonstrate that LHRHa can effectively induce mature sea bass to spawn independent of the highly predictable semilunar spawning rhythm. In addition, the occurrence of both spontaneous and hormone-induced spawnings at a precise period of the day suggest a tidal and diurnal cue entraining spawning of mature female sea bass.

The window pane oyster, Placuna placenta (Linnaeus, 1758), is a highly valuable bivalve species inhabiting the muddy bottom of coastal bays from the Arabian Sea on the west through the Indian Ocean and Malayan Seas to the coast of China on the east (Hornell, 1909). In the Philippines, P. placenta is extensively collected from the wild because of the high demand for its translucent shell, which is fashioned into various articles exported to the United States and Europe. As a result of overharvesting, P. placenta population in some natural beds are already depleted. Therefore, there is a need to conserve this resource through aquaculture. Hatchery techniques should be developed to produce seeds for reseeding and farming purposes. At the Aquaculture Department of the Southeast Asian Fisheries Development Center (SEAFDEC/AQD), Placuna placenta has been induced to spawn by water flow manipulation (Young, 1980). Other methods such as the addition of gametes, temperature shock, and salinity shock are presently being tried. With these induced spawning methods, there is a need to have a high degree of certainly as to the sex of the animal being used. Further, it is important that the method of sexing does not involve sacrificing the animal. However, it has been reported that sexes in P. placenta can be determined only by gonad histology. Rosell (1979) stated that male and the female P. placenta, which are dioecious, are distinguishable upon histological examination of the gonads, but they are without apparent sexual dimorphism. Macsuci et al. (1980) reported that the sex of P. placenta cannot be differentiated except by microscopic examination. Nevertheless, if gonad color, as seen through the translucent shell, could be proven to be a highly reliable basis for sexing, then this method would be useful in broodstock selection. Therefore, this study was conducted to investigate the use of gonad color for sexing P. placenta broodstock.

A simple semi flow-through Artemia culture unit is described for possible integration in marine fish and shellfish hatcheries as source of a cheap nursery diet. The system does not require the use of feeding pumps and involves minimal care. Food preparation and addition to the feeding tank is reduced to one or two manipulations per day during the meta-nauplius stages (day 1–3) and the juvenile stages (day 4–14), respectively. Biomass productions are superior to those reported for stagnant culture systems and are comparable to those demonstrated for flow-through culture units. This simple rearing technique offers the possibility of producing brine shrimp populations with a uniform size. Furthermore, by varying the feeding regime with the Artemia density at the start of the culture, specific Artemia prey sizes corresponding to the daily physical requirements in shrimp and fish hatcheries can be obtained.

Thirteen species of snappers (genus Lutjanus) were identified and sourced for location of capture from surveys conducted at the Iloilo Fishing Port and Central Market. They were Lutjanus argentimaculatus,Lutjanus boutton, Lutjanus carponotatus, Lutjanus decussatus, Lutjanus fulviflamma, Lutjanus malabaricus, Lutjanus monostigma, Lutjanus quinquelineatus, Lutjanus rivulatus and Lutjanus vitta. Incidence of lutjanids was year round with a peak in May. Most abundant and commonly observed were Lutjanus vitta, Lutjanus gibbue and Lutjanus argentimaculatus.

The essential fatty acid (EFA) requirement of milkfish was examined by a 12-week feeding trial using defined, purified diets at water temperature of 28–29°C and salinity of 32‰. The test diets contained varying levels of 18:0 (triglyceride form, TG), 18:3(n−3), 18:2(n−6) and (n−3) highly unsaturated fatty acids (n−3 HUFA). Milkfish juveniles were starved for 7 days and were than fed lipid-free diet for 30 days before the initiation of feeding trials. Low growth and feed efficiency together with high mortalities were observed in fish fed the lipid-free diet as well as in the EFA-deficient diet. Supplementation of 2% 18:2(n−6) to the tristearin based diet did not improve growth rate of milkfish as effectively as feeding with (n−3) fatty acids. The highest weight gain was obtained in milkfish fed a combination of 5% 18:0 + 1.0% 18:3(n−3) + 0.5% 20:5(n−3) + 0.5% 22:6(n−3) although the supplementation of 2% 18:3(n−3) alone or combination of 0.5% 20:5(n−3) + 0.5% 22:6(n−3) to the tristearin based diets were also effective for improvement of growth. Thus, (n−3) fatty acids, such as 18:3(n−3) and (n−3)HUFA were nutritionally more important than 18:2(n−6) for milkfish. The fatty acid composition of the polar lipids from whole body of milkfish juveniles fed the various test diets were influenced by the composition of the dietary fatty acids.

Four practical diets were formulated to contain 0.05%, of the following antioxidants: butylated hydroxytoluene (BHT), butylated hydroxy anisole (BHA), propyl gallate (PG) or ethoxyquin (ETHQ). A fifth diet, with no added antioxidant, served as a control. The diets were fed to Penaeus monodon juveniles to determine the effects of antioxidants on feed quality and growth of the animals. The results showed no significant difference (P> 0.05) between the control and the feeds containing antioxidants in 2-thiobarbituric acid values after 0, 30, 60, and 90 days storage, respectively. There was a significant difference by the 120th day of storage, but no signs of physical deterioration were observed in any of the diets. The highest weight gains (704% and 742%) were obtained with shrimps fed diets with BHT and BHA, respectively, as antioxidants. Hepatopancreatic lesion formation was evident with shrimps fed diets containing antioxidants but not with shrimps fed a diet without antioxidant. Shrimps fed with BHT-added feed showed fewest lesions in the hepatopancreas. Although all shrimp samples given feed containing PG and ETHQ showed lesions, these were patchy in nature and did not affect the growth rates of the animals.