Science / Medicine : Making Waves in the Aquatic Gene Pool : Genetics: Manipulations produce bigger fish, oysters that are tasty year-round and bacteria that discourage barnacles from sticking to vessels.

Fish that grow up to four times normal size, oysters that are tasty year-round and mutant bacteria that discourage barnacles from adhering to hulls.

These and other organisms owe their existence to the manipulation of their genetic material. Research under way with aquatic life promises to revolutionize the aquaculture industry and greatly improve the fuel efficiency of ships.

Because of the potential for economic rewards, much of the work has focused on the improvement of fish and shellfish species already domesticated for pen farms and hatcheries. Much of the new aquaculture work is aimed at enhancing growth rate, improving cold tolerance and directing energy away from reproduction and into meat production.

This has already begun to pay off in decreased operating costs for an industry that is booming. In 1987 alone, Americans bought 7 billion pounds of domestically harvested fish products and imported 9 billion more. Due to advances in genetic engineering, fish farms may soon produce much of this catch cheaper and faster.

The movement began essentially in 1984 in Asia, which accounts for 84% of the world’s aquaculture production. Chinese biologist Zu Yan Zhu transferred human growth hormones into silver goldfish. These transgenic (having genes from another species) fish grew twice as large as their unaltered siblings.

The following year, Zhu transferred bovine growth hormones into loach, a variety of carp pen-farmed in Asia for human consumption, and produced fish quadruple the size of normal loach. Now at the University of Maryland, Zhu continues his work with transgenic fish, pooling his results with those of Dennis Powers of Stanford University and Thomas Chen of the University of Maryland.

In 1986, Powers and Chen, collaborating with Rex Dunham of Auburn University, successfully inserted a rainbow trout gene that regulates growth into carp, thereby creating a new variety that grows to as much as twice the size of normal carp. Transgenic males were then crossed with normal females to yield offspring that inherited the growth gene and grew to more than 50% larger than unaltered control fish.

Dunham has received approval from the U.S. Department of Agriculture to release nine transgenic carp into holding ponds on the Auburn campus to test the fish’s viability outside the lab. Though carp are of limited commercial value in this country, they are useful experimental subjects since males reach maturity in only one year.

For Dunham, catfish are of “primary interest,” given the South’s $4OO-million-a-year catfish industry. Though catfish take as long as four years to mature, the growth gene has already been injected into the fish. Powers said, “There’s ample evidence we’ve got transgenic catfish.” Work has also begun on brackish-water and saltwater species, including striped bass and salmon. In addition, the researchers are preparing to cross transgenic male carp with transgenic females.

Tedious microsurgical methods are used to pierce fish eggs and inject a solution containing the gene into them. The field of transgenic animals is astir, however, due to the recent success of an Italian biologist in transferring foreign genes to mouse eggs by far simpler and less expensive methods that involve incubating mouse sperm cells in a solution containing the genes to be transferred.

While Powers and his colleagues engineer larger fish, biochemist Choy Hew of the University of Toronto has transferred a gene that enhances cold tolerance, from flounder into salmon.

To date, Hew has produced four salmon that contain the flounder gene, and one of the engineered males has been mated with a normal female. “We have every confidence that the gene will carry through to the offspring,” Hew said.

If Hew’s predictions hold true, the implications for the Atlantic salmon industry, especially in New Brunswick, Denmark and Finland, are immense. Enhanced cold tolerance could enable pen-farming to take place in regions that are currently too cold for it.

Improving farm fish is also of keen interest to geneticist Gary Thorgaard and immunologist Sandra Ristow of Washington State University. Sales of Washington-produced aquaculture products topped $25 million in 1987, with salmon production accounting for 42% of those sales.

Working with rainbow trout, Thorgaard has made endrogenic (all-paternal) trout, which contain no genetic material from the female, by irradiating and thereby inactivating eggs into which sperm are introduced. Using genetic markers, researchers have identified offspring that are identical to their parents.

Identical fish could be used in medical studies at greatly reduced costs since mice require 10 to 20 generations to establish genetically identical animals, whereas trout require only two.

Through chemical, heat and pressure-shock treatments of chromosomal material, Thorgaard is also working on developing trout and salmon triploids, fish with an extra set of chromosomes. Triploids have a higher survival rate than diploids (normal individuals with two sets of chromosomes), and because they are sterile, triploids do not expend energy in the production of gonads and so produce more edible body weight faster.

French scientists have induced triploidy in black scallops, and Japanese researchers have done likewise in abalone. Much of the work in this country has focused on oysters, the taste and texture of which significantly decline during the summer months due to gonad production. These reproductive organs can make up close to 80% of the oyster’s body weight during spawning season and are sour, tough and virtually inedible.

Triploid oysters, on the other hand, can be enjoyed in any season. Presently, Westcott Bay Sea Farms in Friday Harbor, Wash., is producing triploid oysters for summertime dining in Seattle restaurants.

There are other problems associated with conventional oyster breeding. Even in protected hatcheries, unaltered oyster larvae sometimes experience as high as 99% mortality rates. University of Maryland scientists Rita Colwell and Ron Weiner have been looking at the mechanisms that make larvae stop floating around and settle to a surface--a requirement before they can undergo metamorphosis and become spat (young oysters).

Colwell and Weiner discovered a new bacterium that secretes material that provides a settling area for the larvae. In laboratory tests, induced bacteria films have resulted in a tenfold increase in overall spat set, when compared to untreated controls.

Weiner and his colleagues have cloned the gene responsible for the synthesis of an enzyme that makes the useful secretions. By manipulating these genes, the researchers are working on making unattractive setting surfaces more attractive. Plastic and cement, for example, are not natural adhesion surfaces but are preferred by hatcheries for a number of reasons.

The adhesion properties of bacteria are also of interest to ecologist Madilyn Fletcher of Maryland’s Center of Marine Biotechnology. Fletcher hypothesized that bacteria may provide a film on which barnacles on the hulls of ships can adhere.

Currently, toxic paints are applied to ships to discourage the growth of algae and barnacles. These paints, however, can have adverse effects on the marine environment. Last year, for example, alarmingly high levels of tributyltin, a chemical used in these paints, was found in mussels along the Southern California coast.

In an effort to diminish the use of these paints, Fletcher has engineered several bacteria mutants and is studying the mechanisms by which barnacles adhere to ships. The results of such work could yield billions of dollars in reduced fuel costs for vessels now encumbered with barnacles.

Other research in aquatic genetics includes gene transformation in marine algae with the goal of enhancing photosynthesis, the cloning of an insulin-like gene in abalone and the development of DNA probes for the detection of water-borne diseases affecting fish and humans.

As aquaculture expert James McVay of the National Sea Grant College Program, a branch of the U.S. Commerce Department, said, “As more species become domesticated, we’re going to see more work in manipulating them to increase productivity and improve their disease resistance. It’s just the next logical step.”