Is small-hold tropical aquaculture in a genetic plunge towards extinction?
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Tropical shrimp aquaculture is in a disease-induced crisis of lost production. The response to this crisis currently focuses on microbiology and pathology, quarantine, and transboundary transfer of shrimp. The crisis also involves an interaction between shrimp genetics and various human interests including protection of intellectual property. Breeders of high-quality strains generally employ (and are encouraged to employ) some form of breeder lock that generates inbreeding when broodstocks are copied . Smaller hatcheries sell these copied, inbred shrimp to farmers, who thereby increase the likelihood of losing their crops to disease. The joint behavior of breeders, hatcheries and farmers causes inbreeding to accumulate in tropical regions. The depressive effect of inbreeding on disease resistance is exceptionally strong in shrimp, as shown in a re-analysis of published field and experimental data. Inbreeding increases the severity and frequency of disease through a variety of mechanisms. We have relatively few, marker-based estimates of accumulated inbreeding in any non-pedigreed shrimp aquaculture system. Simulation shows, however, that locked post larvae (PLs) can be distinguished from copies in broodstocks and farm ponds, given appropriate analysis of genetic markers. Culture of stocks certified to be free of specified pathogens (specific pathogen free or SPF stocks) is strongly recommended and only SPF stocks can now be legally imported into most jurisdictions. These recommendations are appropriate, beneficial and necessary. But insofar as they increase the commercial value of proprietary genetic strains, such regulations may also increase the likelihood of copying, and thus inbreeding at farm level and ever-increasing susceptibility to disease and climate stress (Doyle, 2014a). The intellectual property value of disease-resistant strains will be extremely high and intellectual property rights are fundamental to science-based economic innovation. Breeders will, and must, continue to protect their genetic improvement programs with genetic locks, especially in regions where judicial sanctions are ineffective. The regulatory objective should be to encourage biosecurity and genetic progress while discouraging copying and consequent inbreeding. The current consensus that inbreeding is unimportant may therefore be out of date. Inbreeding may be amplifying the severity of diseases (including the major current threats: white spot syndrome virus or WSSV, infectious hypodermal and hematopoietic necrosis virus or IHHNV and early mortality syndrome or EMS (acute hepatopancreatic necrosis disease or AHPND). Continuing to ignore the interaction between inbreeding and disease may become a fatal error for tropical shrimp aquaculture.
Doyle, R. W. (2015). Is small-hold tropical aquaculture in a genetic plunge towards extinction? In M. R. R. Romana-Eguia, F. D. Parado-Estepa, N. D. Salayo, & M. J. H. Lebata-Ramos (Eds.), Resource Enhancement and Sustainable Aquaculture Practices in Southeast Asia: Challenges in Responsible Production of Aquatic Species: Proceedings of the International Workshop on Resource Enhancement and Sustainable Aquaculture Practices in Southeast Asia 2014 (RESA) (pp. 3-18). Tigbauan, Iloilo, Philippines: Aquaculture Dept., Southeast Asian Fisheries Development Center.
PublisherAquaculture Department, Southeast Asian Fisheries Development Center
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Conference paperR Chou - In F Lacanilao, RM Coloso & GF Quinitio (Eds.), Seminar-Workshop on Aquaculture Development in Southeast Asia and Prospects for Seafarming and Searanching; 19-23 August 1991; Iloilo City, Philippines., 1994 - SEAFDEC Aquaculture DepartmentAquaculture production in Singapore is mainly from Seafarming and is about 2% of total fish consumed. At present, there are 79 licensed floating fish farms located in the East and West Johor Straits that culture popular species like sea bass (Lates calcarifer) and estuarine grouper (Epinephelus tauvina). Aquaculture development is geared towards the establishment of highly intensive fish farms such as land-based systems in agrotechnology parks, smaller brackishwater pond systems, and large-scale floating systems in designated sea areas. Research and development on improvement of farming techniques are on-going.Freshwater aquaculture is focused on ornamental fish production. This is a high value trade with yearly growth of 11 % in 1986-1990. Development of intensive farming systems, improvements in water quality management, disease control, and quarantine are considered important. Research concentrates on breeding and genetics.
Conference paperM Shariff - 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 - SEAFDEC Aquaculture DepartmentHealth management strategies are very important in aquaculture. In Asia, health management practices are broadly similar for the various aquatic species that are cultured. These focus mainly on maintaining the good health of the organisms throughout the life cycle. Good health management is based on an understanding of the interactions between the environment (water), the host, and the pathogens. In an ideal system, the three factors are balanced to offset a disease process. This balance is difficult to maintain in an intensive culture system and significant mortalities usually result. The outbreak of disease is thus related to poor health management. This paper deals with the health management practices applicable to the hatchery and grow-out stages of shrimp and fishes cultured in the tropics.
Conference paperAC 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 - SEAFDEC Aquaculture DepartmentMost 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.