ROCKFISH REPLACEMENTS 



toward making the hybrid the food 

 fish of tomorrow with ease. 



It was relatively simple to cross- 

 fertilize the eggs and produce the 

 hybrid larvae. Then Sea Grant re- 

 searchers at NCSU found that hybrid 

 stripers could be successfully raised in 

 ponds. And researchers soon learned 

 how to inject the striped bass and 

 white bass with hormones that caused 

 them to spawn. 



What wasn't easy was always 

 getting a ready supply of viable eggs. 

 Often the female stripers harvested 

 from the wild were not far enough 

 along in the maturation cycle to 



successfully use available hormones to 

 force them to spawn healthy eggs. 



To comply with state regulations 

 governing the catch of striped bass, the 

 mother stripers had to be caught at the 

 mouth of rivers such as the Roanoke 

 and the Pasquotank, miles away from 



their spawning grounds and days to 

 weeks away from completing their 

 spawning cycle. 



Occasionally, researchers lucked 

 upon a "ripe" female striped bass 

 ready for spawning that produced 

 healthy eggs receptive to white bass 

 sperm. But the success rate was far 

 below what was needed to sustain a 

 growing, thriving aquaculture 

 industry, and the technology didn't 

 allow for a domesticated broodstock. 



Scientists, including Hodson, 

 realized the research needed to take a 

 few steps back before hybrid bass 

 aquaculture could step forward. 



Researchers needed to completely 

 understand striped bass and white 

 bass physiology and most impor- 

 tantly, their reproductive cycles, if 

 the hybrid was going to make a 

 splash on the aquaculture scene. 

 That's why Hodson sought the 



help of Sullivan, a fish gynecologist 

 and a new faculty member at NCSU. 

 Together, the two wrote their first Sea 

 Grant proposal in 1987 for a research 

 project aimed at unlocking the secrets 

 of striped bass physiology. 



The project received funding. 

 Sullivan began his detailed laboratory 

 work at the university while Hodson 

 tested the team's theories and findings 

 in an actual aquaculture setting at the 

 NCSU Aquaculture Research Center in 

 Aurora. 



"First, we did a detailed character- 

 ization of the striped bass," Sullivan 

 says. "We looked at what hormones 

 were present, the actions of these 

 hormones and how to measure them. 

 We developed early pregnancy tests for 

 striped bass females and subjected the 

 fish to ultrasounds and biopsies." 



Striped bass females, like all 

 female fish, make their egg yolks in the 

 liver, and this egg production occurs 

 over a 10-month period. By taking 

 blood samples, Sullivan could deter- 

 mine if a female striper was sexually 

 mature and capable of producing eggs 

 for the next spawning season. 



Then came the larger question of 

 how to force the striper mothers to 

 release eggs, specifically healthy ones 

 capable of hatching larvae. The answer 

 came in the use of a new synthetically 

 produced hormone, GnRHa. 



The hormone is combined with 

 cellulose and cholesterol to form a 

 pellet that can be injected under the 

 skin of a female striped bass. The 

 hormone affects the striper's brain, 

 causing it to release another hormone, 

 called gonadotropin, that sets the fish's 

 reproductive maturation process in 

 motion at an accelerated rate. The 

 hormone works similarly on male 



Continued 



COASTWATCH 15 



