Research on marine and freshwater fishes

Most of the fish research at SEAFDEC AQD in 1992-1994 was on milkfish. Studies were conducted on year-round spawning through hormonal or environmental manipulation; optimum lipid and protein levels and ration size for captive broodstock; and the influence of spawner age on reproductive performance. The economics of hatchery operations, alone or integrated with broodstock as a commercial enterprise, was assessed. Mass production of larvae was refined with the use of commercial or SEAFDEC-formulated larval diets. Alternative rearing schemes in large tanks and ponds were tried. Hatcheryproduced and wild-caught larvae were compared in terms of growth and production in experimental nursery and grow-out ponds. Supplemental diets for brackishwater grow-out culture were formulated. Studies on broodstock management of grouper Epinephelus spp. included lipid enrichment of the diet and hormonal induction of sex inversion. Seed production techniques were developed but survival rates were low. Grouper culture was found economically feasible in experimental ponds with 'trash' fish as feed. The mangrove red snapper Lutjanus argentimaculatus was successfully induced to spawn with injection of human chorionic gonadotropin. Initial larval rearing trials were successful but survival rates must be improved. Hormonal manipulation of spawning of the Asian sea bass Lates calcarifer allows seed production during most of the year. Photoperiod manipulation leads to maturation of females, but not males, beyond the natural breeding season (April-November). Nursery rearing of 9 mm juveniles is feasible in floating net cages with night lights that attract food zooplankton. The requirements of sea bass for lipid, protein, carbohydrates, and essential amino acids were determined. In the rabbitfish Siganus guttatus, weekly injections of luteinizing hormone releasing hormone analogue (LHRHa) sustains milt production for three weeks. Thyroid hormones injected into broodstocks improved the growth of larvae to day 7. Induced spawning techniques for the Asian catfish Clarias macrocephalus were refined by determining the seasonal responsiveness to LHRHa and pimozide injections and testing for pheromonal induction of spontaneous spawning. The optimum insemination rate was determined and egg hatchability was enhanced by removal of the adhesive coat before incubation. Several practical diets for catfish during grow-out culture were tested against 'trash' fish. The broodstock management for bighead carp Aristichthys nobilis was studied. Cage-reared juveniles from cage-reared broodstock showed the best growth. To improve the reproductive performance, the broodstock diets were supplemented with vitamins A, C, and E. Research on tilapias focused on genetics and strain selection. Several strain testing procedures for Nile tilapia were evaluated in their efficiency to detect economically important strain differences. Reference lines were developed from two existing red tilapia strains to measure and reduce the effects of uncontrolled nongenetic variables in strain evaluation experiments with Nile tilapia. The tolerance of two Nile tilapia strains to heavy metals was similar when gauged by the 24-hour and 96-hour lethal concentration and by fish growth, survival, and reproductive performance. In a separate study, four strains of red tilapia showed generally higher seed production when reared in tanks than in cages. Improvements in the feed and feeding management for Nile tilapia were also studied. Intensive tilapia farming and feeding have led to oxygen depletion and fish kills in Sampaloc Lake. To rehabilitate the lake, it is imperative to reduce the farming area from 30 to 6 hectares; stop the use of commercial feeds; and remove the water hyacinths and other debris. Fish kills in Laguna de Bay have also become serious in recent years, and a review of the occurrences, losses, and possible causes is currently being conducted. Studies on the epizootic ulcerative syndrome of snakeheads in Laguna de Bay have yet to pinpoint the pathogen. Skin lesions in tilapias in several ponds and lakes in the country were found to be due to bacteria

Milkfish, rabbitfish and mullet

This paper reviews studies conducted on milkfish (Chanos chanos), rabbitfish (Siganus guttatus), and mullet (Mugil cephalus) at the SEAFDEC Aquaculture Department from 1968 to 1991. Milkfish studies focused on hormonal induction of off-season gonadal maturation, dietary manipulation of milkfish broodstock to improve egg and larval quality, improvement of larval rearing techniques for mass fry production and technology transfer to the private sector, and search for a low-cost, practical diet for milkfish and a supplemental diet to increase pond production. Preliminary success on alternate feed for larval rearing and spontaneous maturation of milkfish in concrete tanks may help alleviate milkfish fry supply in the future. Studies on rabbitfish centered on improvement of larval survival and search for the optimum diet for growth of rabbitfish fry and juveniles reared in ponds. The difficulty in rearing rabbitfish larvae due to high mortality at first week after hatching hinders the development of the rabbitfish industry. Research involving mullet was solely on the establishment of broodstock for fish propagation

Updates in the Philippines: Where are the captive milkfish breeders?

A map is provided showing the location of milkfish rearing facilities in the Philippines. Most of the 17,443 milkfish broodstocks are located in central Philippines. A table shows details as to the rearing facility (cage, pen, pond, tank), number of broodstocks, and age. There are 13,420 broodstocks in ponds; 2,081 in cages; 842 in tanks, and 1,100 in pens. The youngest is 3 years, the oldest 23 years old

Aquaculture of the mangrove red snapper

Mangrove red snapper (Lutjanus argentimaculatus) is an important marketable species throughout the Indo-Pacific region. It is a euryhaline species; it can tolerate freshwater, brackishwater and marine water. Modular culture is the common system in snapper production in the Philippines. Stocking density is 4,000 fry per cropping; there could be 2 croppings per year. Brief details are given of investment costs and returns for culture in brackishwater pens

Changes in lipid and fatty acid content during early larval development of milkfish (Chanos chanos): influence of broodstock diet

Abstract only.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

Hormonal, environmental, and dietary manipulation of milkfish broodstock to enhance egg production

The insufficient supply of milkfis fry severely limits the expanion of milkfish aquaculture. While natural spamning and hatchery production of milkfish fry have been attained recently, there is sitll a need to incease egg production from available broodstock. A number of studies geared towards this concern are currently conducted at SEAFDEC Aquaculture Department with moderate success. Chronic administration of estradiol-17B and 17A-hydroxy-progesterone to femaleand male milkfish broodstock increased maturation and rematuration rates. Milkfish kept under constant long phtoperiod (16L:8D) appeared to have prolonged gonadal development than thoes of milkfish reared under long to normal to short photoperiod. Ffrmulated diet containing 6% liquid that is feed to milkfish broodstock at a daily ration 4% of total body weight appeared sufficient for maintaning sexual maturation andspawning. Refinements in these areas canensure a better management technique that can provide maximum number of good quality eggs required by hatcheries

Maturation and induced spawning of the mangrove red snapper (Lutjanus argentimaculatus) reared in a floating net cage in the Philippines

Wild-caught mangrove red snapper (Lutjanus argentimaculatus) were reared in a floating net cage at SEAFDEC/AQD's Igang Marine Substation at Guimaras Island, Central Philippines. In 1993, monthly samplings and induced spawning trials were conducted as part of a project on seed production. Gonadal development began in February for males and April for females, reached a peak in September and declined in December. Males and females had ripe gonads for up to 5-6 consecutive months. Spawning occurred in the evening (2000 to 2300 hours), 32-36 hours after a single intramuscular injection of 1,500 IU human chorionic gonadotropin kg-1 body weight (BW). About 0.53-2.14 million eggs were collected per female (2.5-4.4 kg BW) with fertilization rates of 21-97% and hatching rates of 42-80% resulting in 30-85% normal larvae (straight and without deformities). The results strongly suggest the feasibility of breeding mangrove red snapper in floating net cages