Tilapias are important foodfishes in the Philippines second only to milkfish. While farming of tilapias in freshwater ponds and cages is already established, there is a need for wider application of the available technologies for brackishwater culture. This paper presents the tilapia species used for brackishwater farming and the commercial methods applied for their hatchery/nursery rearing.

Milt volume, sperm density, and number of spermatozoa were determined to quantify milt production of mature sea bass after a single injection of LHRHa [(D-Ala6,Pro9-N-ethylamiide)LHRH] in saline solution and 17α-methyltestosterone in corn oil (MT). Two measures of sperm density, sperm count and spermatocrit, were highly correlated (r=0.85). Compared with control, milt volume and the number of spermatozoa collected increased but sperm count decreased (24% at 24 h) after a LHRHa (20 µg/kg body weight treatment, suggesting a stimulation of spermatozoa production and not merely milt dilution. Further milt dilution (44%) was induced by 80 µg/kg LHRHa (LHRHa80) at 12 h post-treatment but not by 200 µg/kg MT (MT200) alone. A milt dilution of only 27% at 12 h after simultaneous injections of LHRHa80 and MT200 may indicate some inhibitory effect of MT on the efficiency of LHRHa. These results demonstrate that the stimulation of milt production by LHRHa involves testicular hydration resulting in milt dilution.

Venturing into the aquaculture sector especially in pond and cage culture is a step that has been taken up by entrepreneurs and traditional fishermen of Sabah. However, shortage in the supply of fish fry is a stumbling block to the progress of the industry. The Sabah Fisheries Department has taken steps to overcome this problem by setting up a hatchery with the objectives to transfer know-how on hatchery technologies to the private sector besides producing fry for distribution. The Tanjong Badak multi-species hatchery is a newly established hatchery, completed in mid-1990. The species reared for production purposes are tiger shrimp and finfish which include red snapper, grouper, sea bass and polkadot grouper. The Department has not close to producing sea bass fry. Shrimp fry at juvenile stages (PL 40) are distributed as subsidies to local fish farmers while some are reared at the Department's various cage and pond culture projects. Limited success in producing grouper and red snapper fry have been achieved to date. The incidence of very low fertilization rates of eggs coupled with low survival rates are major problems facing the hatchery. In conclusion, the Sabah Fisheries Department's experience in fish larval rearing is still limited. Greater scientific research and studies need to be carried out to improve further the performance of the hatchery to achieve the target of fry sufficiency for the aquaculture industry.

The first part of the study investigates the ability of ovine growth hormone (oGH) to enhance the hypo-osmoregulatory and growth performance of juvenile brown trout after exposure to sea water (SW). Three groups of fish were either intraperitoneally implanted with cholesterol pellet (sham) or with a cholesterol pellet containing 250 µg oGH (treated) or not implanted (control). While still in fresh water (FW), gill Na+/K+ATPase activity of the oGH-treated group was four times higher than that of sham and control groups. Exposure to SW resulted to dramatic increases in plasma electrolyte levels of the sham and control groups, whereas the oGH-treated group showed only minor perturbations in plasma electrolyte concentrations. Further increases in gill Na+/K+ ATPase activity were observed in the oGH-treated group after SW exposure, while in the sham and control, a lag time of seven days was needed before gill ATPase activity started to increase. Additionally, by the end of the experiment, oGH-treated fish were significantly larger than non-treated ones. The second part of the study examines the time course of changes in plasma GH levels and GH free binding sites and affinity of the organs involved in osmoregulation in juvenile brown trout kept in FW or exposed to SW. Plasma GH levels increased significantly one day after SW exposure, reaching a peak on the 14th day. Concomitantly, GH free binding sites in the gills and liver decreased significantly in trout exposed to SW but remained unchanged in trout kept in FW. Reduction in GH free binding sites in SW-exposed trout indicates occupation of the gill and liver GH receptor by GH during the course of SW adaptation which may point to a direct role of GH on gill and liver physiology during hypo-osmoregulation. The second part of the study examines the time course of changes in plasma GH levels and GH free binding sites and affinity of the organs involved in osmoregulation in juvenile brown trout kept in FW or exposed to SW. Plasma GH levels increased significantly one day after SW exposure, reaching a peak on the 14th day. Concomitantly, GH free binding sites in the gills and liver decreased significantly in trout exposed to SW but remained unchanged in trout kept in FW. Reduction in GH free binding sites in SW-exposed trout indicates occupation of the gill and liver GH receptor by GH during the course of SW adaptation which may point to a direct role of GH on gill and liver physiology during hypo-osmoregulation.

Research on seed production of several foodfishes has been a continuing activity of SEAFDEC/AQD since 1976. Fry and juvenile production methods of these fish commodities are in various stages of advancement. For instance, advances in the development of hatchery rearing, particularly feeding and water management schemes, have made mass production of milkfish (Chanos chanos) seed a reality, resulting further in the application of the technology in commercial hatcheries. Recent studies now focus on assessing the quality of hatchery seed stocks of milkfish vis-a-vis wild seed during nursery and grow-out culture. Likewise, sea bass (Lates calcarifer) seed production has undergone significant improvements since the technology was introduced in the Philippines in 1982. Fatty acid-enrichment of a zooplankton diet can enhance growth and survival of sea bass fry, although other cheaper alternatives and early weaning to formulated diet preparations are currently being tested. Hatchery fry production of grouper (Epinephelus salmoides and E. suillus syn. E. coioides) and snapper is in its infancy, but trials complemented by research on their larval feeding habits and requirements are underway to establish reliable methods of rearing larvae of these species. Although fairly well-established, seed production of rabbitfish (Siganus guttatus) requires further improvement in determining an appropriate zooplankton diet to ensure adequate growth and survival of larvae. Hatchery fry production of tilapia (Oreochromis sp.), carps (Aristichthys nobilis, Hypothalmichthys molitrix) and, to a certain extent, catfish (Clarias macrocephalus) can already be categorized as a flourishing industry in some parts of the Philippines. Nonetheless, SEAFDEC/AQD continues to conduct research on these freshwater species, with particular emphasis on nutrition and feed development during the nursery production phase. Together, results of past and on-going research studies ensure that seed supply of these important foodfishes become adequate and sustainable for the grow-out.

The application of the bioencapsulation technique as a tool for curative treatment in fish larvae was investigated. Antibacterials, trimethoprim (TMP) and sulphamethoxazole (SMX), incorporated in an oil emulsion (SELCO, Artemia Systems N.V., Ghent, Belgium) were bioencapsulated at different concentrations (20% and 40%) in Artemia (Instar II) nauplii. Chemotherapeutics-loaded nauplii were fed to European sea bass (Dicentrarchus labrax) larvae only once at 5 individuals/ml. Larvae were sampled after feeding at time intervals 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 12, 16, 20, 24, 36, 48, 60, 72 h. Drug concentrations in the larval tissue were analyzed by high-performance liquid chromatography (HPLC). Results indicated that larvae fed 40% "medicated"-Artemia assimilated significantly higher levels of chemotherapeutics in the tissue as compared with those fed 20% "medicated"-Artemia. Chemotherapeutics given at higher concentration (40%) reached peak levels (19.3 µg TMP/g DW, 23.32 µg SMX/g DW) in the larval tissues within 2 h while at lower concentration (20%) peak levels (8.74 µg TMP/g DW, 6.73 µg SMX/g DW) were observed within 5 h. Moreover, TMP persisted longer (>72 h) in the tissues than SMX (12-16 h) suggesting a more efficient uptake and retention of TMP and/or faster metabolism and elimination of SMX.

The feeding habits of hatchery-reared Epinephelus suillus larvae were determined by examining their gut contents. The larvae (2.6 mm TL) were initially fed rotifers on day 2 and newly-hatched Artemia nauplii on day 21 (9.1 mm TL). The amount of rotifers initially ingested averaged 1.3 individuals/larva. The ingestion rate increased as larvae grew. Larvae immediately showed strong preference for Artemia to rotifers on the first day of introduction. E. suillus larvae showed diurnal feeding pattern at day 7 (3.6 mm TL), day 14 (4.9 mm TL), day 21 (9.1 mm TL) and day 28 (11.1 mm TL). Feeding incidence decreased in the evening and was nil at 2100-2200 h. Active feeding started earlier in older larvae and satiation was between 0900-1000 h. The results of this study will be used as a basis in developing a good feeding scheme for E. suillus larvae.

In the past, larviculture of milkfish depended entirely on the use of rotifers and brine shrimp nauplii and rearing trials were done under roofed facilities. Since the dietary value of live food varies according to culture and feeding conditions, rotifers were enriched with SELCO, a lipid emulsion containing high levels of highly unsaturated fatty acids (HUFA) prior to feeding the larvae. Alternatively, a microbound larval feed (Nosan R-1) was given as a supplement to rotifers during the first two weeks of culture. Larval growth was enhanced and survival was significantly improved when rotifers were enriched or supplemented with these diets. All rearing trials were conducted in 5-10 tons concrete circular/rectangular outdoor tanks. Verification runs on the use of HUFA-enriched rotifers to milkfish larvae were tried in two nearby private hatcheries. Results from mis collaborative work are presented.

Ovaries of Oreochromis mossambicus exposed to sublethal concentrations of nickel sulphate (0.5 mg/1 and 1.0 mg/1) were histologically analyzed. Changes following exposure to 0.5 mg/1 nickel sulphate include irregularities in the shape of egg follicles, subcellular oocyte damage, lifting off of the theca layer and proliferation of connective tissues. In the ovaries exposed to 1.0 mg/1 nickel sulphate, degenerative changes are worse. Invasion by connective tissues is extensive, oocytes have bizarre shapes, yolk granules are scattered in the interfollicular spaces, abnormal growths are evident and previttelogenic oocytes abound. Nickel is a toxicant in Oreochromis mossambicus ovaries.

The influence of amount and type of lipid given to milkfish broodstock by developing larvae was investigated by feeding broodstock commercial diets that differed in lipid content and composition. The two commercial feeds used had the following proximate composition: RFP - 28.16% crude protein, 2.40% crude fat, 7.58% crude fiber, 53.94% N-free extract; RCP - 43.28% crude protein, 4.58% crude fat, 6.18% crude fiber, 37.0% N-free extract. The lipid content and fatty acid composition of spawned milkfish eggs reflected that of the broodstock feed. Percent lipid in egg from broodstock fed RFP and RCP dropped by 22.5% and 26.9% in newly-hatched larvae and by 53.0% and 65.0% in day 2 larvae (>90% yolk resorbed), respectively. Decreases in total PUFA and increase in monoenoic fatty acids during yolk resorption indicate that milkfish as in other marine fishes utilize PUFA during early larval development. While differences in rate of utilization of individual n-3 and n-6 FA in two groups of larvae seem to be influenced by levels of the fatty acids in eggs, the influence of other nutrients on fatty acid utilization need to be investigated.