the fish and time consuming for the operator. To improve on this, scientists developed a single-injection technique in which the hormones are embedded in a matrix of large molecules; the hormones are released slowly from the matrix over a long period of time leading up to spawning. This method is now used in farming striped bass and other fish.

In some operations, ironically, fish farmers risk losing much of their marketable stock because their fish mature too soon. If fish come into breeding condition at too young an age, they increase operating costs and may be too small to sell profitably. Precocious maturation of salmon was a big problem for salmon farmers in British Columbia until technologies for controlling reproduction turned things around. Using both hormonal and genetic controls, researchers developed techniques for sterilizing fish and developing strains in which few or no males were produced. Approximately 80 percent of the chinook salmon currently cultured in British Columbia are all-female strains. Sterilizing those grown for market prevents them from maturing, giving operators better control over marketing time and product size.

The dense populations, genetic uniformity, and stress found on commercial fish farms make them a paradise for bacteria and viruses. Where large commercial aquaculture operations grow and spread, so, too, do many infectious diseases. The threat of disease may, in fact, be the biggest factor limiting the development of aquaculture worldwide. Many millions of dollars are at risk in