‘Sex-reversed’ salmon a valuable goal

Press, 10 July 1985, Page 35

‘Sex-reversed’ salmon a valuable goal

Sex may not be out of the question, but it is certainly out of the ordinary for several hundred salmon at a New Zealand Marine Farms, Ltd, site in the Marlborough Sounds. The three-year-old fish appear no different from thousands of other quinnat salmon in the company’s sea cages, except that they may be “sex-reversed.” Unique to New Zealand seas, the salmon are part of a New Zealand Marine Farms research and development programme aimed at improving methods of raising sea-farmed salmon to full maturity.

The company’s chief executive, Dr Paul O’Connor, said the salmon farm-

ing industry has much to gain if the experiment is successful. “A major economic factor in farming salmon is that a large proportion of male fish become sexually mature after two years,” he said. “Unfortunately, the energy normally used for growth with these sexually precocious fish is diverted to the development of their reproductive organs and the result is a small, earlymaturing fish.” The precocious males can be harvested and marketed as pan-sized salmon of about one to I.skg, Dr O'Connor said. But the sale price is not nearly as good as large, full-grown salmon

which command premium prices. “The big question is how to avoid or significantly reduce the number of precocious males, thereby lowering production costs and increasing operating efficiency.

“Overseas trout farmers, for example, are breeding and raising sex-reversed trout which grow to enormous size, but no-one as yet has been able to achieve the same results with quinnat salmon. “NZ Marine Farms has undertaken . a complex breeding programme that includes sex-reversal of female fish to give them male sexual characteristics. “When this broodstock

produces the next generation, we expect to have predominantly female fish. Thus we reduce the incidence of precocious males.” By introducing sexreversed fish into breeding programmes, a high percentage of female salmon could be maintained from year to year, Dr O’Connor said. If NZ Marine Farms can achieve this goal it will give the New Zealand salmon farming industry an advantage over all competitors. “There are big financial rewards for companies that can grow larger numbers of salmon to adulthood and meet the demand for premium full-sized fish on world markets,” he said.