Clarissa L. Marte

The Food and Feeding Habit of Penaeus Monodon Fabricius Collected From Makato River, Aklan, Philippines (Decapoda Natantia) 1)

The food of Penaeus monodon Fabricius collected from Makato River, Aklan, consisted mainly of Crustacea (small crabs and shrimps) and molluscs, making up 85% of ingested food. The remaining 15% consisted of fish, polychaetes, ophiuroids, debris, sand, and silt. Results indicate that P. monodon is more of a predator of slow-moving benthic macroinvertebrates rather than a scavenger or detritus feeder. Feeding activity (determined from stomach fullness) of female prawns is significantly higher than that of males. Preliminary experiments on foregut clearance revealed that clearance rate is rapid with 95% of food transported from the foregut 4 hours after feeding. Feeding behavior of P. monodon appears to be associated with the tidal phase. A significantly higher mean gut fullness index indicative of increased feeding activity, was noted when the tide is on the ebb.

Induced spawning of sea bass, Lates calcarifer, and rabbitfish, Siganus guttatus, after implantation of pelleted LHRH analogue

Abstract Captive Lates calcarifer broodstock at Tigbauan, Iloilo (Philippines) were implanted with cholesterol-based pellets of the LHRH analogue D-Trp6-desGly10-LHRH ethylamide or D-hArg(Et2)6,Pro9-NHet-LHRH at doses between 9.0 and 23.5 μg/kg body weight. In May, one of ten LHRH-treated females released partially hydrated ova into the tank 4 days after implantation. In July, at least one (and probably four) of five LHRH-treated females spawned in the tank 2 days after implantation; 2.6 million hatchlings were collected. In August, both LHRH-treated females spawned in the tank 2 days after implantation; 978 000 hatchlings were collected. None of the sham-operated control fish spawned in any of the experiments. Captive Siganus guttatus broodstock implanted with silastic-based pellets of the LHRH analogue D-Nal (2)6 LHRH spawned 1–2 days earlier than sham-operated controls.

Spontaneous maturation and spawning of milkfish in floating net cages

Abstract Milkfish ( Chanos chanos Forsskal) reared from wild-caught fry and from hatchery-bred fry matured at 3.5–5.5 years (2.3–4.9 kg). Maturation and spawning of the hatcherybred fish marks the first time the milkfish life-cycle has been completed in captivity. Milkfish at various stages of gonadal development were obtained in July–October 1980 and March–June 1981 derived from wild-caught fry, and in February–June 1983 from the hatchery-bred fish. The fish were held in floating net cages 9 m and 10 m diameter by 3 m deep, located in 7 m deep water off Igang, Guimaras Island, Philippines. Annual ranges of temperature and salinity were 25–33°C and 25–38 ppt, respectively. The fish were fed commercial feed pellet (42% protein) at 1.5–2% of body weight twice daily. Sexual maturation occurred during the natural breeding season of wild milkfish in the nearby waters. Gonadosomatic index (GSI) of mature males was 0.32–3.95 (wild-caught, 0.32–3.95; hatchery-bred, 1.71–3.85). For mature females it was 1.24–8.12 (wildcaught, 1.56–7.62; hatchery-bred, 1.24–8.12). Two spawnings were recorded in August 1980 and eight in May–July 1981 from the broodstock derived from wild-caught fry, with 342–6293 eggs collected from each spawning, while 14 spawnings were observed in May–June 1983 from the hatchery-bred fish, with 770–114 000 eggs collected. The time of spawning was between 23.00 and 02.00 h. Fertilization rate was 55–99% for the broodstock from wild-caught fry and 47–100% for the hatchery-bred fish. Hatch rate varied from 9 to 80%. Factors affecting spontaneous maturation, spawning and rematuration are discussed. Although slight improvements in egg collection were obtained, further innovations in egg collecting techniques will have to be developed. The results indicate the potential for hatchery production of milkfish fry from captive broodstock and for restocking of waters deprived of naturally occurring fry.

Larviculture of marine species in Southeast Asia: current research and industry prospects

Abstract The increased requirement for food fish, the lucrative market for expensive seafood, and the need to conserve marine resources, have motivated the rapid pace of larviculture research in Southeast Asia. Various research and academic institutions in Southeast Asia such as the Southeast Asian Fisheries Development Center Aquaculture Department (SEAFDEC AQD) are carrying out research on commercially important marine species including 10 fish, 6 crustacean, and 7 mollusk species. Since fry availability is a major constraint in the development of culture systems, a major research thrust of SEAFDEC AQD is the development of commercially viable technologies for breeding and seed production of commercially important marine fish and crustaceans such as milkfish, groupers, snappers and mud crabs, in addition to the production of fry and juveniles of endangered and depleted species such as the sea horse and the tropical abalone for stock enhancement and sea ranching. Although hatchery production of milkfish and sea bass are now commercially viable enterprises, research is being pursued to improve fry quality through feed supplementation and to lower production cost by using alternative live or artificial feeds. Larviculture techniques are being developed for technically demanding species such as groupers and snappers. The recent success in larviculture of the mud crab Scylla serrata is expected to stimulate the growth of the mud crab industry in the region. Similarly, encouraging developments in the breeding and larviculture of the sea horse and mollusks such as the tropical abalone will provide the necessary support to carry out future stock enhancement and sea ranching programs for these species.

Induced spawning of maturing milkfish (Chanos chanos Forsskal) with gonadotropin-releasing hormone (GnRH) analogues administered in various ways☆

Abstract The response of mature female captive milkfish to mammalian and salmon gonadotropin-releasing hormone analogues (mGnRH-A and sGnRH-A) was investigated. Prior to spawning, six groups of three females received (1) 10–16 μg mGnRH-A from an osmotic pump implanted intraperitoneally (IP); (2) 100 μg mGnRH-A from a cholesterol/cellulose pellet implanted IP; (3) 10 μg/kg mGnRH-A as an intramuscular (IM) injection; (4) 10–16 μg sGnRH-A from an osmotic pump implanted IP; (5) 100 μg sGnRH-A from a cholesterol/cellulose pellet implanted IP, and (6) a cholesterol/cellulose pellet without analogue implanted IP. The most effective treatment was 100 μg sGnRH-A/fish given in a cholesterol/cellulose pellet; all ( 3 3 ) of the fish spawned. However, mGnRH-A was more effective ( 2 3 ) compared with sGnRH-A ( 1 3 ) if osmotic pumps were used to administer GnRH-A. If the dose and method of administration were not considered, then the salmon and mammalian GnRH analogues were equally effective (62–67%) for induction of ovulation and natural spawning in milkfish. Gonads of control fish regressed. At the doses tested, injections or pellet implantations were more effective compared with osmotic pumps. All pellet-implanted and injected females responded to treatment and 75% ( 6 8 ) spawned; half ( 3 6 ) of the pump-implanted females spawned. Spawning occurred from 18 to 36 h after treatment.

Induced spawning of maturing milkfish (Chanos chanos) using human chorionic gonadotropin and mammalian and salmon gonadotropin releasing hormone analogues

Abstract The response of maturing female milkfish to D-Ala6-des Gly10 mammalian GnRH ethylamide (mGnRH-A), D-Arg6-des Gly10 salmon GnRH ethylamide (sGnRH-A) and human chorionic gonadotropin (hCG) was investigated. The GnRH analogues and hCG were equally effective when administered by intramuscular injection at doses of 10 μg/kg and 100 μg GnRH-A/fish or 1000 IU hCG/fish. All of the females injected with HCG and 87.5% ( 7 8 ) of females injected with GnRH-A spawned. Pellet implantation of the GnRH analogues, however, was less effective based on 100 μg of pellet per fish, which provided from 20 to 36 μg of analogue per kg fish. Fish implanted with mGnRH-A or sGnRH-A showed responses which varied from oocyte hydration to spawning. Only 3 7 implanted with mGnRH-A and 1 7 implanted with sGnRH-A spawned; in the latter group, the average egg diameter was 11–17% smaller at the time of treatment compared with the other treated groups. Except for one, all fish with egg diameters above 0.65 mm had hydrated/ovulated oocytes or spawned. Females which spawned had egg diameters above 0.71 mm.

A collecting gear for naturally-spawned milkfish (Chanos chanos Forsskal) eggs in circular floating net cages

Abstract A collecting gear for naturally-spawned milkfish ( Chanos chanos Forsskal) eggs in circular floating net cages is described. The gear has been shown to be effective in collecting large numbers of eggs. The collecting gear can be adopted for other broodstock fish species held in circular floating net cages.

Induced gonadal maturation and rematuration in milkfish: Limited success with chronic administration of testosterone and gonadotropin-releasing hormone analogues (GnRH-A)

Abstract Nine experiments were conducted to investigate the influence of chronic administration of testosterone (T) and gonadotropin-releasing hormone (GnRH) analogues on first maturation of 4- to 6-year-old fish and rematuration of 6- to over 9-year-old spent/regressed fish. Implantation of T or T in combination with luteinizing hormone-releasing hormone analogue (LHRH-A) had no marked effect on maturation rate of 4-year-old milkfish. The percentage of maturing fish was low and similar to controls in Experiment 1 (T, 31–35%; control, 35%) and Experiment 3 (T, 13%; T plus LHRH-A, 28%; control, 22.2%). Most of the 4-year-old maturing fish were males; maturing females were obtained only from the T-implanted groups in Experiment 1. In Experiment 3, T-implanted maturing females were able to retain yolky eggs whereas maturing control females did not, indicating that testosterone may have enhanced vitellogenesis and maintained the integrity of vitellogenic oocytes. Tank-reared maturing 4-year-old females, about half the size of older first maturing females, were induced to spawn. This is the first case of maturation and spawning of 4-year-old milkfish reared in tanks. As in Experiments 1 and 3, the percentage maturation of spent fish in Experiments 7 and 8 was similar for T-implanted and controls. On the other hand, the 4-year-old immature fish in Experiments 2 and 4, the 5- and 6-year-old immature fish in Experiments 5 and 6, and the spent 6-year-old fish in Experiment 9 were immature or regressed throughout. The factors which may have influenced the results of these experiments include age and reproductive history of the fish, timing of hormone implantation, experimental and holding conditions, and stress.

An improved method for collecting naturally spawned milkfish eggs from floating cages

Abstract Natural spawnings of captive milkfish ( Chanos chanos Forsskal) held in floating cages were observed in 1980, 1981, 1983 and 1985. Frequency of spawnings increased from two in 1980 to 41 in 1985. Various collectors and collection methods were tried with only slight improvements in number of eggs collected. Although the number of eggs collected per spawning increased from 900 in 1980 to a maximum of 769 000 in 1985, the numbers were not sufficient for mass-scale fry production. The most urgent problem was egg predators inside the floating cages during the spawning season. This paper presents an improved method of egg collection using fine-mesh net cages (“hapa” nets, 1 mm mesh) which effectively prevented entry of egg predators. Before “hapa” nets were installed the number of eggs collected ranged from 3300 to 668 000. From 330 000 to 2 942 000 eggs were collected by using “hapa” net cages. With the new method mass-scale production of milkfish fry can be achieved.

Hormonal changes accompanying sexual maturation in captive milkfish (Chanos chanos Forsskal).

Steroid hormone profiles accompanying sexual maturation in captive milkfish are described. There were no significant differences in levels of serum estradiol 17-β (E2) and testosterone (T) between immature male and female fish. Mean E2 levels rose from 0.54±0.11 ng/ml in immature females (Stage 1) to 4.53±1.16 ng/ml in vitellogenic females (Stage 5), while T levels increased from 2.06±0.28 ng/ml to 38.4±9.26 ng/ml. E2 and T levels were positively correlated to GSI and oocyte diameter. In males, serum T levels increased from 2.5±0.40 ng/ml in immature males to 27.73±5.02 ng/ml in spermiating males. A significantly higher T level was found in males with thick and scantly milt (spermiation index, SPI, 2) compared to males with scanty milt (SPI, 1) or males with copious, fluid milt (SPI, 3).Serum levels of E2 and T, and the GSI in females rose significantly during the breeding season (April–June 1983). The levels of both steroids dropped below 1 ng/ml in spent females sampled in succeeding months. In immature males, T levels ranged from 1.11 ng/ml to 2.78 ng/ml and rose significantly to 21.52±8.38 ng/ml during the breeding season when GSI peaked. Serum T levels dropped to around 10 ng/ml in the succeeding months when only spent or regressed males were sampled.