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.

Cryopreserevation of different strains of Brachionus plicatilis symmetrical stage embryos was conducted. One S-type strain, namely Yashima-S (YS), and three L-type strains, namely Yashima-L (YL), Nagasaki (NG), and Hamana (HA), were used. Symmetrical stage embryos in 10% DMSO-28‰ sea water solution were frozen at -196°C using a two-step freezing procedure; the embryos were first cooled slowly from -5°C to -20°C at a rate of 0.3°C/min and then cooled rapidly by direct transfer to liquid nitrogen. Frozen samples were thawed in a gently stirred water bath at room temperature. A mean survival rate of 36% after 30 days storage in liquid nitrogen of HA strain was significantly lower than YS (55%), YL (58%), and NG (54%), and is due likely to its relatively larger embryo volume. There was no significant difference in the intrinsic rate of increase (r) between strains among clones taken from the cryopreservation or unfrozen control group. The results also indicate that various strains of B. plicatilis embryos can be cryopreserve without seriously altering their reproductive capability. The freezing method described could be of great potential in aquaculture and in future studies on rotifer genetics.

Effects of unilateral eyestalk ablation on wild and pond-reared Penaeus monodon during ovarian maturation were determined by examining the growth (e.g., carapace length, body length, body weight) and reproductive (e.g., gonad weight, gonadosomatic index (GSI), average and maximum oocyte diameter) parameters to compare their reproductive potential. Growth parameters were similar in the wild unablated and wild ablated prawns from the immature or previtellogenic (P) to mature or cortical rod (C) stages but increased during the immature (P) to maturing or vitellogenic (V) stages in the pond ablated prawns. During stage C, gonad weight was highest in the wild unablated group while GSI, average and maximum oocyte diameter was similar in the three groups. After spawning (stage S), gonad weight was similar in all groups but GSI, average and maximum oocyte diameter were higher in the pond ablated prawns than in the wild unablated and wild ablated groups. Changes in growth and reproductive parameters at various stages of maturation suggest that reproductive performance successively decreased in the wild unablated, wild ablated and pond ablated P. monodon.

The effects of supplemental feeding on milkfish growth, production, survival, water quality, and economic benefits in brackishwater ponds were evaluated by comparing a rice bran diet, containing 11.3% protein, and two pelleted diets, containing 22.0% and 27.4% protein, with an unfed control. Four 800-m² tide-fed ponds, subdivided into quarters, were used. Each treatment was replicated in four random pond compartments. Milkfish with initial average weight of 1 g were stocked at 8000/ha and feeding commenced when the average weight and standing crop were 57 g and 417 kg/ha, respectively. All supplemental feeds significantly (P<0.05) increased growth and production over the unfed control. Feeding diets containing 22.0% and 27.4% protein resulted in 35.3% and 46.7% higher net profits, respectively, whereas feeding rice bran resulted in a 34.4% lower net profit when compared to the unfed control. The growth of milkfish became significantly slower (P<0.01) than those fed the 27.4% protein diets when the standing crop of unfed and rice bran-fed fish reached 535 kg/ha and fish fed the 22.0% protein diet reached 972 kg/ha. Survival was not significantly different among the treatments. The concentration of metabolites in the culture water for all treatments was low but a significant increase (P<0.05) in level of total carbon dioxide and nitrite-nitrogen was observed as biomass increased.

The study was undertaken to determine the effect of 0, 25, 50 and 75% replacement of organic matter in the feed with rice straw compost on milkfish (Chanos chanos) growth and production. Treatments have similar organic matter and nitrogen loads. Up to 50% substitution (Treatments 1 to 3) was possible without significantly affecting fish growth and yield (668–725 kg/ha). A significant reduction in growth and yield (456 kg/ha) with 75% substitution (Treatment 4) implies that organic matter from compost did not contribute much to fish growth. Low phosphorus content of compost and inadequate phosphorus load in spite of increasing mineral input from compost resulted in similar primary productivity in all treatments. It appeared that compost was not a satisfactory feed substitute and that the fish derived most of their nutrition from the feed. The results further suggest that yield could be economically increased by using a low protein diet (23.8%) given at a lower rate (1.75% of body weight). To further improve yield, feeding rate can be gradually increased as biomass increases, although the most cost-effective ration will depend on the fish capacity to grow under certain environmental conditions.