Development in Marine Finfish Culture

C.W. Laidley. R.J. Shields. A.C. Ostrowski

The Oceanic Institute

Marine Finfish Program

41-202 Kalanianaole Hwy.

Waimanalo, HI 96795

claidley@oceanicinstitute.org

Abstract

The aquaculture potential of finfish species inhabiting the warm pelagic waters of the tropical and subtropical Pacific ocean have only recently become a target for aquaculture development in the US. Although a basic understanding of the biology and physiology of these high value species lags well behind that of most cultured fish, the vast untapped potential of these aquatic resources makes them an attractive avenue for aquaculture development. Previous experience with established culture species in combination with modern biotechnology using molecular tools will lead to a rapid development of aquaculture practices, and provide new approaches to resolving existing challenges. These tools can be applied to all stages of culture technology including reproduction, genetic selection, larval rearing, and animal health.

Key Words: Marine finfish, reproduction, genetic selection, larval first feeding, disease

Introduction

The Oceanic Institute is currently undertaking the development and transfer of biotechnology for ten species of warm-water marine finfish for aquaculture and stock enhancement purposes. Although the development of new aquaculture species has classically been a long and tedious process engaging the research activities of many researcher groups at multiple locations, previous experience gained with current cultured species, combined with modern biotechnological approaches could greatly accelerate these developments. Such approaches are just beginning to be used in the US and are well established in Japan.

Through our experience in culturing multiple species at the Oceanic Institute, we have identified several critical "bottlenecks" that are relevant to broad groups of cultured finfish species. These bottlenecks include disease diagnosis and treatment, reproductive dysfunctions, poor or variable growth, and poor larval survival. Although the potential of modern biotechnology is far too broad to review here, we will provide several examples in which modern approaches can be applied to help resolve specific bottlenecks.

Disease Diagnosis and Treatment

The captive culture of any organism results in some degree of chronic stress due to the highly artificial nature of the culture system and the inability of animals to effect compensatory changes. In addition to compromised growth and reproduction, chronic stress lowers an organism’s resistance to disease and often leads to infection by opportunistic pathogens. There is a need to apply molecular approaches to develop a better understanding of immune system function, develop new cost-effective diagnostic tools that can be transferred between species, and develop new therapeutic techniques to enhance resistance or provide treatment upon detection of disease outbreaks. Alternative approaches including the development of disease resistant culture strains and commissioning of bio-secure systems will also require the development of similar technologies.

Reproductive Dysfunction

An essential cornerstone to industry success is the development of controlled reproduction technology providing a reliable seedstock supply. Despite good survival and excellent growth rates, broodstock of many species do not reproduce, or produce inferior gametes under the conditions of captive culture. The cost of reproductive dysfunction is huge due to the considerable investment in capturing and maintaining broodstock animals. Added to this is the subsequent dependence of hatchery, nursery, and growout or stock enhancement operations on a reliable seedstock supply. Although the application of hormonal induction protocols using mammalian hormones have in some cases provided a means to generate seedstock supply on demand, these treatments have rarely been optimized for the target species, often produce inferior quality gametes, and compromise the health of valuable broodstock.

Although there has been considerable investment in foundational research in reproductive physiology and endocrinology for a number of intensively cultured finfish species, there have been remarkably little application of these tools to questions relating to applied finfish culture. The more recent molecular techniques developed to study mammalian reproductive physiology, and recently applied to salmon and several other commonly cultured finfish species, could greatly facilitate studies on reproductive function in warm-water marine species. Molecular probes using highly conserved sequence regions can be used to follow gene expression of reproductive hormones (GnRH, GtH-I and II) or their receptors in new species. Further, molecular approaches can expedite reproductive hormone assay development as a tool to elucidate the underlying physiological changes accompanying reproductive function and dysfunction leading to improved gamete quality and a more reliable seedstock supply.

Genetics and Growth

Although many marine fish species exhibit exceptional growth under conditions of captive culture, growout is still the most costly phase of culture operations and therefore has the greatest potential monetary gain from application of modern biotechnical approaches. Like other areas of agriculture, significant improvements can be gained through genetic selection for improved growth or increased disease resistance. Animal domestication and selection for desirable traits predates the advent molecular genetics by thousands of years. Modern approaches offer efficient tools to identify and quantify genetic variability, whether the objective is to select desirable culture traits or maintain stock diversity. In particular, the application of microsatellite markers to quantify population variability and identify heredity provides a rapid and cost-effective tool to aid selection programs.

Associated with the development of desirable strains is a need to develop effective reproductive sterilization protocols to prevent wild-species contamination from onshore culture or accidental offshore releases. Although a number of chemical, physical, and genetic approaches have been developed, none are cost-effective or sufficiently reliable and, thus, new approaches are needed to understand sex determination and the control of sexual development.

Larval Mortality

The culture of many of the pelagic spawning marine finfish species is limited by the small size and environmentally sensitive nature of newly hatched larvae. Problems arising from inappropriate nutritional composition of prey or incomplete prey digestion are critical for larvae during the transition from endogenous to exogenous feeding. Furthermore, mass mortalities of larvae have frequently been attributed to adverse microbial conditions encountered under intensive culture conditions.

Molecular approaches provide opportunities to characterize gastrointestinal development that are complementary to currently used microscopic and biochemical techniques. PCR-based assay can facilitate the detection of fish-specific digestive enzyme expression during larval development, to aid implementation of species appropriate larval diets. PCR amplification may also be utilized to profile both environmental and gastrointestinal microflora, in order to elucidate the interactions between bacteria and larvae during early life history stages.

Recommendations

Short term (1-3 years) Collaborate with existing biotechnology/molecular research groups to apply and evaluate existing techniques from human medicine and agriculture toward critical issues in aquaculture.

Mid term (4-7 yrs) Develop on-site capabilities to incorporate successful biotechnologies into aquaculture research programs for evaluation of end use applications. Particular emphasis on molecular markers and diagnostic tools.

Long term (8-10 yrs) Technology transfer of relevant technology to commercial operations with emphasis on the development of diagnostic kits and commercialization of new technologies.

Acknowledgements

We wish to acknowledge the support of the U.S. Department of Agriculture and the National Oceanographic and Atmospheric Administration for their continued support.