Now showing items 1-6 of 6

    • Article

      Advanced broodstock diets for the mangrove red snapper and a potential importance of arachidonic acid in eggs and fry 

      AC Emata, HY Ogata, ES Garibay & H Furuita - Fish Physiology and Biochemistry, 2003 - Springer Verlag
      Mangrove red snapper fed advanced broodstock diets containing squid meal and squid oil exhibited higher hatching rates, cumulative survival and survival activity index than those fed a basal diet or a basal diet supplemented with mixture of antioxidants. On the other hand, fatty acid analyses of ovaries and fry of wild fish and eggs and larvae of broodstock fed raw fish revealed high arachidonic acid (ARA) and docosahexaenoic acid (DHA) levels and relatively lower eicosapentaenoic acid (EPA) levels consequently showing high ARA/EPA and DHA/EPA ratios compared to cold water species. This suggests that ARA may be nutritionally more important for egg and larval development and survival in tropical marine fish and its supplementation in broodstock diets may enhance reproductive performance of mangrove red snapper.
    • Book

      Management of milkfish broodstock 

      AC Emata, CL Marte & LMB Garcia - 1992 - Aquaculture Department, Southeast Asian Fisheries Development Center
      Series: Aquaculture extension manual; No. 20
      The manual on milkfish (Chanos chanos) broodstock management covers the following topics: reproductive biology; sources of broodstock; holding facilities for broodstock; feeding; determination of gonadal development; spawning and egg collection; transport of spawned eggs; determination of percent viable eggs; and determination of hatching rate.
    • Article

      A practical broodstock diet for the mangrove red snapper, Lutjanus argentimaculatus 

      AC Emata & IG Borlongan - Aquaculture, 2003 - Elsevier
      A practical broodstock diet (39% protein, 8.6% lipid) was formulated for the mangrove red snapper as part of a project to ensure consistent production of good quality eggs and larvae through broodstock nutrition. Reproductive performance of mangrove red snapper broodstock fed practical diet (n=14 females) was enhanced in comparison to those fed raw fish (n=12 females). Broodstock fed practical diet had total egg production of 82.34 million from 68 spawns for two spawning seasons while broodstock fed raw fish produced 77.64 million eggs from 66 spawns. Mean percent of egg viability, hatching rates and percent of normal larvae did not vary between the two groups. However, broodstock fed the practical diet had higher mean cumulative survival rate of eggs to normal larvae (40.4%) than that of broodstock fed raw fish (35.2%). Also, survival activity index (4.08) of broodstock fed practical diet was higher than that of broodstock fed raw fish (2.97). The results clearly indicate the improvement of reproductive performance of mangrove red snapper fed practical diet. Further studies should focus on the specific nutrients that can ensure consistent production of high quality eggs and larvae of the mangrove red snapper to support its aquaculture.
    • Article

      Reproductive performance in induced and spontaneous spawning of the mangrove red snapper, Lutjanus argentimaculatus: a potential candidate species for sustainable aquaculture 

      AC Emata - Aquaculture Research, 2003 - Blackwell Publishing
      A reliable breeding technique was developed for the mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775), to help sustain the aquaculture of this immensely popular species in Southeast Asia. Using standardized indices of female maturity (based on mean oocyte diameter of ≥0.40 mm), time of injection (1000–1130) and sex ratio (one female to two males), a single injection of 100 μg kg−1 luteinizing hormone-releasing hormone analogue (LHRHa) (n=16 fish), but not 50 μg kg−1 (n=five fish), successfully induced egg (62.5% success rate) and larval (43.8%) production. Human chorionic gonadotropin (hCG) at 500 IU kg−1 (n=five fish) also failed to induce spawning, but doses of 1000 (n=22 fish) and 1500 IU kg−1 (n=15 fish) gave spawning (77.3% and 80.0% respectively) and hatching success rates (72.7% and 60.0% respectively) that were not significantly different from those of 100 μg kg−1 LHRHa. No spawning was observed in saline-injected controls (n=seven fish). While mean spawning latency, egg diameter, egg production per spawn, percent egg viability, hatching rate, percent of normal larvae and cumulative survival of eggs to normal larvae did not differ significantly among the effective hormones and doses, 1000 IU kg−1 hCG had a higher percentage (76.5%) of total spawns with egg production per spawn in excess of one million than those of 1500 IU kg−1 hCG (50.0%) and 100 μg kg−1 LHRHa (40.0%). Mangrove red snapper spontaneously spawned from March–April to November–December with a peak of egg collection and spawning in May–June. Egg collection per spawn ranged from 0.05 to 6.35 million. Spontaneous spawning of mangrove red snapper exhibited lunar periodicity with spawns mostly occurring 3 days before or after the last quarter and new moon phases and occurred consistently between 02:00 and 04:00 hours. High fecundity and good egg quality, coupled with the ability to respond to induce spawning or natural spawning in captivity, provide a sound basis for improving the sustainability of red snapper aquaculture in Southeast Asia.
    • Conference paper

      Research on marine and freshwater fishes 

      AC Emata - In TU Bagarinao & EEC Flores (Eds.), Towards sustainable aquaculture in Southeast Asia and Japan: Proceedings of the Seminar-Workshop on Aquaculture Development in Southeast Asia, Iloilo City, Philippines, 26-28 July, 1994, 1995 - Aquaculture Department, Southeast Asian Fisheries Development Center
      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.
    • Article

      Salinity tolerance of larvae of the mangrove red snapper (Lutjanus argentimaculatus) during ontogeny 

      CB Estudillo, MN Duray, ET Marasigan & AC Emata - Aquaculture, 2000 - Elsevier
      Salinity tolerance and the effects of salinity on growth, condition factor and chloride cell (CC) densities were evaluated for Lutjanus argentimaculatus larvae during ontogeny. Tolerance of L. argentimaculatus larvae to abrupt changes of salinity from 32 ppt varied with age. Periods to 50% mortality (LT50) were significantly (P<0.05) longer for 0-day-old larvae than for 7-, 14- and 21-day-old larvae. Tolerance of abrupt salinity change increased remarkably, starting on day 28. Although abrupt transfer to test salinities caused substantial mortalities, L. argentimaculatus larvae, regardless of age (0-, 7-, 14-day-old), showed significantly longer LT50 when abruptly transferred to 8 and 16 ppt than for transfers to 24 and 40 ppt (P<0.05). Growth of L. argentimaculatus larvae at 16, 24, 32 (control) and 40 ppt was not significantly different either at the end of the first rearing phase (days 0–21) or second phase of rearing (days 22–50). Survival was significantly lowest at 40 ppt (4.3%) at the end of first phase of rearing (P<0.05). There were no significant differences in survival rates at the end of the second phase of rearing; however, the condition factor (K) of larvae reared at lower salinities was significantly higher than that of fish at 40 ppt (P<0.05). Gill epithelia of 42- and 50-day-old larvae showed increasing density of CC with increasing salinity.