Now showing items 21-28 of 28

    • Book chapter

      Reproductive biology of the Asian seabass, Lates calcarifer 

      EG de Jesus-Ayson & FG Ayson - In DR Jerry (Ed.), Biology and Culture of Asian Seabass Lates Calcarifer, 2014 - CRC Press
    • Article

      Reproductive development of the threatened giant grouper Epinephelus lanceolatus 

      The giant grouper is presumed to follow the reproductive pattern of most Epinephelus species, characterized by protogynous hermaphroditism wherein male maturation is attained through sex reversal of a functional female. This hypothesis, however, has not been verified due to lack of biological data. The present study addresses this gap by investigating the reproductive development of giant groupers from juvenile stage through sexual maturity. Gonad histological analysis of hatchery-bred juvenile giant grouper from Queensland, Australia (0.8–5.2 kg, n = 43) have shown earliest occurrence of primary oocytes (i.e. ovarian differentiation) in 47.8 cm and 2.5 kg fish. Monitoring of sexual maturity by gonadal biopsy was performed in a stock of wild-caught giant groupers (2–52 kg) held in sea cages in the Philippines and Vietnam from 2015 to 2017. Onset of female sexual maturity was at 96.9 ± 1.6 cm and 23.5 ± 1.5 kg in the Philippines, and 103.0 ± 4.1 cm and 33.5 ± 2.5 kg in Vietnam. In both locations, development of primary males was observed wherein fish produced milt (or spermiated) without passing through a functional female phase. The ratio of primary males to females in both locations was about 1:2. Size at maturity of primary males is 86.5 ± 4.8 cm and 17.1 ± 2.1 kg in the Philippines, and 97.3 ± 1.3 cm and 34.3 ± 0.9 kg in Vietnam. To aid in the monitoring of female maturation, we developed a non-invasive method based on immunoassay of vitellogenin in skin mucus and this was shown to be effective in detecting female maturation 9 ± 2 months prior to first observation of oocytes through gonadal biopsy. Our findings suggest that giant grouper is a diandric protogynous hermaphrodite. This study provides novel information on the reproductive biology of giant grouper, an economically important and vulnerable species.
    • Book

      Sea bass hatchery operations. 

      MM Parazo, LMB Garcia, FG Ayson, AC Fermin, JME Almendras, DM Reyes Jr., EM Avila & JD Toledo - 1998 - Aquaculture Department, Southeast Asian Fisheries Development Center
      Series: Aquaculture extension manual; No. 18
      The manual addresses sea bass (Lates calcarifer) fry production in the hatchery. It describes the principles and practical procedures for rearing sea bass - from eggs until metamorphosis - as practiced by the SEAFDEC Aquaculture Department in Tigbauan, Iloilo, Philippines. It is presented under the following main section headings: General principles; biology; Selecting a suitable site; Design - tank systems, seawater supply system, freshwater supply system, aeration system, other facilities; Broodstock - source of breeders, breeding techniques; Egg collection, transport and hatching; Larval rearing - stocking density, feed types and feeding management, water management size-grading of larvae; Harvest and transport of fry; and, Propagation of larval food - Chorella, Brachionus, Artemia, Moina.
    • Book

      Seed production of rabbitfish Siganus guttatus 

      FG Ayson, OS Reyes & EGT de Jesus-Ayson - 2014 - Aquaculture Department, Southeast Asian Fisheries Development Center
      Series: Aquaculture extension manual; No. 59
      This manual is mainly intended to serve as a practical guide to fishfarmers and other stakeholders interested to venture in operating a rabbitfish hatchery. It details site selection, hatchery design & layout, and protocols in broodstock management, spawning, larval rearing, and harvest & transport. It has also a section on natural food production for rabbitfish larvae.
    • Article

      Survival of young rabbitfish (Siganus guttatus Bloch) under simulated transport conditions 

      FG Ayson, MM Parazo & DM Reyes Jr. - Journal of Applied Ichthyology, 1990 - Blackwell Publishing
      The effect of loading density, transport duration, water temperature, and salinity on survival of young rabbitfish (Siganus guttatus Bloch) under simulated transport conditions was investigated. The rocking motion of transport was simulated by an electric shaker. At ambient temperature and salinity (28°C/32‰S) increasing loadin density and transport duration resulted in decreasin fish survival rates. When both temperature ant salinity (20°C/20‰S) were lowered survival improved sinificantly. Dissolved oxygen, water temperature, and salinity were critical factors affecting survivaf of young rabbitfish during simulated transport. Based on the results, a density of 100 fish/L can be packed for 8 hours of transport and 300 fish/L for 2 hours at 28°C and 32‰, and about 200 fish/L for 4 hours at 20°C and 20‰S.
    • Book chapter

      Sustainable milkfish production in marine fish cages through strong government support and effective public-private partnerships: a case study from Panabo City Mariculture Park in Davao del Norte, Philippines 

      FG Ayson, AM Ventura & EG de Jesus-Ayson - In W Miao & KK Lal (Eds.), Sustainable intensification of aquaculture in the Asia-Pacific region. Documentation of successful practices, 2016 - FAO Regional Office for Asia and the Pacific
      This case study presents the successful practice of sustainable intensification of milkfish aquaculture in marine fish cages under semi-intensive grow-out conditions in the Panabo City Mariculture Park (PCMP) in Davao del Norte, Philippines. Established in 2006, PCMP became operational through the promulgation of a City Ordinance declaring 1 075 hectares of municipal waters in Panabo City as a Mariculture Development Zone/Park. The operations of PCMP were so successful that in just five years it became the third largest among the 63 operational MPs in the Philippines during 2011, with 86 private investors-locators operating a total of 322 units of cages. At present, a total of 372 units of fish cages are operating in the mariculture park (MP). A combination of factors contributed to the successful operation of PCMP, but the success is usually attributed to the effective partnership between the government (both local and national) and the private sector. The Comprehensive MP City Ordinance that governs the PCMP is strictly implemented and includes, among others, the tenurial rights and access to locators. Regulations on distances between cages are strictly enforced and security measures in the total area are jointly undertaken by the government and the locators. The national government, through the Bureau of Fisheries and Aquatic Resources-National Mariculture Center (BFAR-NMC), provides technical support in all aspects from stocking to harvest during the production cycle. BFAR-NMC staff conduct regular periodic sampling of the stocks and compute feeding rates for the stocks which are implemented by the technicians/caretakers. Likewise, BFAR-NMC staff regularly monitor the water quality of the MP and the health status of the stocks. Since it became operational in 2006, the PCMP did not report a single incident of mass fish kill, which indicates that the technical guidelines of MP operations are strictly followed. Workers are trained and organized into groups by BFAR-NMC such as caretakers, cage framers, netters, harvesters, fish processors, and others, and actively participate in discussions related to MP operations to ensure protocols are properly followed. Harvests of stocks are done by skilled workers trained by BFAR-NMC, all done in the “Bagsakan Center” or fish landing area and are well-coordinated. The support facilities in the fish landing area are provided by both the local and national government and the PCMP Producers Association. The operators provide complete data for their operations to BFAR-NMC for record keeping. The strong partnership between the national government through BFAR-NMC, the local government unit, the investors, as well as the acceptance and support from the community for the PCMP is the hallmark of its success.
    • magazineArticle

      Sustaining environmental integrity in the midst of intensified aquaculture development 

      FG Ayson, T Azuma, T Shibuno, BO Acosta & VT Sulit - Fish for the People, 2015 - SEAFDEC Secretariat
      The escalating aquaculture production from Southeast Asia during the past decades seems inevitable notwithstanding its significant contribution to economic growth and guaranteed food security of the countries in the region. Despite its good prospects, the region’s aquaculture sector is being confronted with various issues that should be addressed to enable it to develop sustainably and contribute unceasingly to poverty alleviation in the region. Responsible aquaculture has been practiced in the region as means of easing the crisis in capture fisheries; however, this has to be matched with effective approaches that address concerns on the fishery resources that are deteriorating. Resource enhancement of economically important aquatic species has been considered as one of the effective approaches that would help protect and restore the aquatic resource habitats and stocks, the latter connotes stock enhancement. As could be gleaned from the current scenario of fisheries in the Southeast Asian region, the recurring over-exploitation of common natural resources has affected the livelihoods of fishers and coastal communities. The imbalanced extraction of natural aquatic resources and natural recruitment has worsened through the years and if left unabated could result in the extinction of many of the region’s endemic aquatic species. It is for such consequences that the Aquaculture Department of the Southeast Asian Fisheries Development Center, while intensifying its efforts in developing sustainable aquaculture, is also promoting resource enhancement as these two approaches are expected to enhance the region’s fishery resources and food security in view of their perfect roles in improving the productivity of aquatic stocks and status of the natural habitats. Nonetheless, aquaculture techniques have always been used to facilitate the stock enhancement of commercially important, threatened and endangered aquatic species. The National Oceanic and Atmospheric Administration of the USA defines stock enhancement as “restoration aquaculture” or the release of hatchery-bred juveniles of fish and shellfish to the wild, and considers this approach as a management tool to recover depleted stocks due to overfishing and habitat loss. The Food and Agriculture Organization of the United Nations has demonstrated that stock enhancement is a type of culture based fisheries since part of the life cycle of certain aquatic species is being controlled in hatcheries before the seeds or juveniles are transplanted or released into open waters — freshwater or brackishwater or marine environments — and allowed to propagate or grow on natural foods until reaching harvestable size.
    • Article

      Thyroxine injection of female rabbitfish (Siganus guttatus) broodstock: changes in thyroid hormone levels in plasma, eggs, and yolk-sac larvae, and its effect on larval growth and survival 

      FG Ayson & TJ Lam - Aquaculture, 1993 - Elsevier
      The thyroid hormone levels in female rabbitfish, Siganus guttatus, plasma, eggs, and yolk-sac larvae were measured before and after thyroxine (T4) injection in female spawners at doses of 1, 10, and 100 μg T4/g body weight (BW) fish. T4 and triiodothyronine (T3) levels in maternal plasma, eggs, and yolk-sac larvae were elevated following T4 administration. Apparently, there is conversion of T4 into T3 in the broodfish which suggests the presence of the enzyme, 5′-monodeiodinase, in rabbitfish. T4 and T3 in maternal circulation were easily transferred into the oocytes and subsequently into the larvae. Larvae from spawners treated with 10 and 100 μg T4/g BW tended to be longer and showed sornewhat better survival compared to the control and those injected with 1 μg T4/g BW 7 days after hatching. These findings suggest that thyroid hormones may play an important role during early larval development of rabbitfish.