A rising tide - Biotechnology: A Resourceful Gene

IT is only a decade since marine biotechnology was first recognized as an area of great potential. In that short span of time astonishing progress has been made.

Some of the most striking advances have been in the aquaculture industry, where direct genetic manipulation using recombinant DNA techniques has made it possible to develop an entirely new approach to fish farming. This is important because of the significant expansion of aquaculture in recent years. According to some estimates aquaculture may be supplying 25 per cent of world seafood consumption by the end of the century.

Fish are highly amenable to genetic manipulation because their eggs are large and can therefore be injected with DNA constructs. Major research efforts in genetic manipulation have been directed towards enhancing the growth and production of fish with superior resistance to cold temperatures. With the spread of intensive fish farming and the concomitant increased risk of disease, the development of disease-resistant fish has also become an increasingly important objective.

Goldfish with a human gene

The first successful growth hormone experiment using fish was the transfer into a goldfish of the human growth hormone gene, yielding offspring significantly larger than untreated fish. Since then, several vertebrate genes have been introduced into fish species, including Atlantic salmon.

Of more practical significance has been the achievement of growth enhancement using fish growth hormone. In several experiments, fish injected with growth hormone reached double the weight increment of untreated fish over a sixty-day period. However, as growth hormone is not easy to administer to fish, research is now focusing on generating transgenic fish. Up to 1990, thirteen transgenic fish species had been reported, including transgenic variants of commercial varieties such as the Atlantic salmon, channel catfish, carp and tilapia. Research is now underway to determine the physiological, nutritional and environmental factors that maximize the performance of transgenic fish. Major problems of safety and environmental impact must also be solved before large-scale, commercial production of transgenic fish will be permitted.

Antifreeze for salmon

Genetic manipulation of Atlantic salmon has been carried out to try and increase the resistance of this species to cold. Many marine fish that live in cold water produce proteins which act as an "antifreeze" and protect them by inhibiting the formation of ice crystals in their serum. Atlantic salmon lack genes for the production of these proteins and therefore cannot survive in icy waters. However, genes coding for antifreeze proteins have now been transferred to Atlantic salmon, and the expression of adequate concentrations of these proteins in their blood could extend the range of environments where this fish can be grown.

Shellfish are also amenable to genetic manipulation, especially for enhancing their rate of growth and their size. It has been shown that bovine growth hormone can enhance the growth rates of California red abalone, and similar results have been reported for the application of biosynthetic rainbow trout growth hormone to young oysters.

Unlike fish and shellfish, anthropoids such as lobsters shed their exoskeletons during growth by means of a moulting process that is under hormonal control. Thus, regulation of moulting by the hormone-secreting endocrine gland may improve growth efficiency in the lobster. However, knowledge of the molecular genetics of marine crustaceans such as shrimp, lobster and prawns must be expanded before commercial production of these species will be efficient and reliable. Growth, development, and disease resistance have yet to be controlled.

One factor on which the successful exploitation of a fish or shellfish species in aquaculture depends is the ability to obtain consistent, controlled reproduction as economically as possible. It has been shown that water temperature and the period of daily illumination the fish receive can be manipulated sufficiently to improve spawning. Fortunately, some important advances have been made recently in the use of hormone treatment to control reproduction of fish species that are important in aquaculture.

The farming of marine macroalgae--sea-weed--has been practised for several centuries in Asian countries, particularly Japan, and products derived from them have been widely used as sources of medicine and food. Macro- and microalgae yield a wide range of products, including food additives and supplements, culture media, pesticides, plant growth regulators and antibacterial, anti-cancer and antiviral agents.

Seaweed for medicine and food

Microalgae have proved useful for large-scale production of fatty acids which may help to reduce the risk of coronary vascular disease. The green microalga Dunaliella salina is grown in large-scale, intensive culture in California to produce beta-carotene, a substance associated with the prevention of cancer. It has also been suggested that oceanic farming of marine algae could reduce global carbon dioxide levels.

The application of biotechnology to the cultivation of marine algae presents an opportunity for countries near rivers and the ocean, especially developing countries with extensive coastal regions. This potential is most likely to be realized by the formation of partnerships with industrialized countries. However, to achieve success, an understanding of molecular genetics and an application of the techniques of modern molecular biology will be required. Although molecular techniques have not yet been widely applied to achieve strain enhancement or the production of transgenic plants and algae of commercial importance, this approach is now being adopted in several laboratories in the United States, Asia and Europe.

Marine organisms are sources of a very wide range of natural products that have biomedical, biotechnological, agricultural and industrial applications. Chitin is one such product that has made it to market in a variety of forms--as poultices to heal wounds, extenders, and emulsifiers for photography--yet still remains a focus of extensive study. If and when the genes for chitin synthesis are cloned, the production of this compound will increase immeasurably since a stable source can then be obtained.

In the past decade, more than 1,000 new compounds, natural products, and other discoveries relating to the molecular genetics of fish and shellfish growth, metabolism and reproduction have been recorded. Promising new antibiotics, anti-cancer therapeutic agents, improved aquaculture stocks and food additives have either been discovered or are in the development stage. Where once only a few pioneers toiled in their laboratories, there are now major new centres of biotechnology research and development in Norway, Japan, the United States and elsewhere.

RITA COLWELL, of the United States, is President of the University of Maryland Biotechnology Institute. Adviser to several public bodies, national and international, she is a member of the Executive Board of the International Council of Scientific Unions and of the Scientific Advisory Committee of the United Nations University's Biotechnology in Latin America and the Caribbean programme. She is the author or editor of 16 books, author or co-author of several hundred papers and articles and produced an award-winning documentary, Invisible Seas, on marine microbiology.

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