Fish of a different breed 



For years, scientists manipulated 

 the genetics of plants — corn, tomatoes, 

 cucumbers — to develop hybrids. This 

 manipulation allowed farmers to get 

 more and better food to the American 

 table faster. 



Now UNC Sea Grant scientists are 

 applying genetic manipulation to fish. 

 The striped bass. Howard Kerby and 

 Mel Huish, zoologists at N.C. State 

 University, are crossing striped bass 

 with white bass or white perch to 

 develop a hybrid. 



Today this type of genetic manipu- 

 lation is loftily called biotechnology. 

 But its aim is more down-to-earth — to 

 produce hardier, faster growing 

 hybrids that can be raised commer- 

 cially in culture conditions. 



Kerby and Huish chose to work with 

 the striped bass because of its declining 

 natural stocks. Commercial and 

 recreational fishermen have long 

 sought the striped bass for its highly 

 prized meat. But as stocks declined, 

 the fish became harder to find. To save 

 the fishery, resource managers in 

 states along the East Coast have 

 begun limiting commercial catches. 

 (Such a regulation was being con- 

 sidered by the N.C. Marine Fisheries 

 Commission when Coastwatch went 

 to press.) 



A substitute was needed to fill the 

 commercial demand for the striped 

 bass and to remove pressure on the un- 

 stable natural population. The hybrid 

 answers both these needs, offering 

 culturists an opportunity to produce a 

 high quality, high-priced fish. 



But Kerby and Huish's work goes 

 beyond just crossing striped bass with 

 white perch and white bass. They are 

 genetically manipulating the fish to 

 improve the production potential of 

 the hybrid and to develop a 

 domesticated hybrid brood stock. The 

 development of a brood stock would 

 alleviate the need to collect scarce wild 

 fish and would streamline the produc- 

 tion of hybrids for culturists. 



At a recent striped bass workshop 

 sponsored by UNC Sea Grant, Kerby 

 put his genetic knowledge on display. 

 Female striped bass taken from the 

 wild during the spawning season were 



injected with hormones to induce 

 ovulation. Twelve hours after the fish 

 were injected, Kerby began sampling 

 the eggs to predict when they would 

 ripen. Upon ripening, the eggs were 

 manually squeezed from the females. 

 Likewise, sperm were squeezed from 

 white bass males. 



Kerby produced gynogenetic diploid 

 and triploid hybrids. What does this 

 mean, you ask? Well, it's all in the 

 chromosomes. 



A diploid is any fish with a normal 

 number of chromosomes. Like humans, 

 most fish have 48 chromosomes. 



To produce gynogenetic diploids — 

 essentially clones — Kerby irradiates 

 the sperm from the male fish to 

 destroy its chromosomes. After the 

 sperm fertilizes the females' eggs, the 

 eggs are heat- or cold-shocked or 

 chemically treated to retain an extra 

 set of chromosomes the female usually 

 ejects. The fish still ends up with 48 

 chromosomes, but they are all con- 

 tributed by the female, making the fish 

 a virtual clone of its mother. 



Using this process, Kerby can cross 

 striped bass with white bass or white 

 perch to produce hybrids, then clone 



Photo by Dou^ Yoder 



Howard Kerby tests the water for dissolved oxygen 



