FISHERY BULLETIN: VOL. 69. NO. 1 



maintained on long photoperiods (16 hr of light) 

 remained in spawning condition for 2 months 

 (at 22° C) or 3 months (at 14° C) beyond the 

 normal season. 



6. At 14° C, injection of mature fish with 

 salmon pituitary, carp pituitary, chorionic go- 

 nadotropin from human pregnancy urine 

 (HCG), and deoxycorticosterone acetate (DO- 

 CA) caused increases in gonad size over sham- 

 injected or uninjected fish. 



7. A single injection of 1 mg (acetone dried) 

 salmon pituitary, 50 lU of gonadotropin from 

 pregnant mare serum (PMS) or 50 lU of HCG 

 induced spawning in mature croakers (50-100 g) 

 with gonad index values about 5 "^.'f . Fish with 

 gonad index values below about 5 ^r did not re- 

 spond to otherwise adequate hormone doses. 

 Hormone-spawned fish could be spawned a sec- 

 ond or third time at 1- to 2-month intervals. 



8. Eggs could be stripped from the fish an 

 average of 30.4 hr following injection. This 

 latent period consisted of a slow hydration phase 

 of water uptake followed by a rapid ovulation 

 phase which released eggs from the follicles in- 

 to the ovarian lumen. 



9. The eggs remained viable only for 1 to 2 hr 

 following ovulation, unless they were stripped 

 from the fish and stored in moist chambers. 

 Each female produced 700 to 1000 eggs per gram 

 of wet body weight. 



10. Sperm are viable for less than 30 sec after 

 dispersion in water. 



11. Low dosages (0.1 mg) of salmon pituitary 

 were insufficient to cause hydration, while very 

 high dosages (5 mg) caused hydration but, evi- 

 dently, inhibited ovulation. High dosages (100 

 lU) of HCG caused fish to overhydrate and 

 eventually die without having ovulated. 



12. Carp pituitary caused hydration but was 

 inadequate for ovulation. Deoxycorticosterone 

 acetate and oxytocin, given alone, had little or 

 no effect on the fish. 



13. Fish did not respond to single hormone in- 

 jections if the water temperature was at or be- 

 low 17° C. One day of acclimation to a higher 

 temperature was sufficient to prepare fish from 

 cold water for spawning. 



14. A few larvae hatched from eggs obtained 



by hormone-induced spawning were reared 

 through metamorphosis; thus, the entire life 

 cycle of the gulf croaker can be completed under 

 laboratory conditions. 



ACKNOWLEDGMENTS 



Many people contributed to the total success 

 of this project, a cooperative effort made pos- 

 sible by Alex Calhoun, Chief of Inland Fisher- 

 ies, California Department of Fish and Game, 

 and Reuben Lasker, Program Director for Be- 

 havior and Physiologj', National Marine Fish- 

 eries Service Fishery-Oceanography Center, La 

 Jolla. Their interest made possible the funds 

 and facilities for this study, supported by Fed- 

 eral Aid to Fish Restoration Funds, Dingell- 

 Johnson Project California F-24-R, "Salton Sea 

 Investigations." 



Robert F. Elwell, Senior Research Supervisor, 

 IFB, Sacramento, saved me from many admin- 

 istrative details and provided aid and encour- 

 agement at critical points in time. Fred Murin, 

 Salton City, was my able field assistant and com- 

 panion; and David Crear, now at the University 

 of Hawaii, was of inestimable value in our lab- 

 oratory ventures. Robert C. May. Scripps In- 

 stitution of Oceanography, La Jolla, contributed 

 much of his time to the successful completion 

 of the study. 



Technical assistance was provided by Charles 

 F. Wright and Bert D. Kitchens, National Ma- 

 rine Fisheries Service Fishery-Oceanography 

 Center, La Jolla, who built the fish-holding facil- 

 ities and maintained the critical seawater sup- 

 ply. W. H. Jochimsen and D. R. Von Allmen, 

 Nimbus Fish Hatchery, Rancho Cordova, ar- 

 ranged for me to collect salmon pituitaries. Da- 

 vid Powell, Curator of Fishes, Sea World-San 

 Diego, taught me how to transport and care 

 for fish, and Vince Catania, California Deiiart- 

 ment of Fish and Game at Antioch, showed me 

 how to capture Salton Sea fishes. To each of 

 these persons I extend my gratitude for their 

 help, interest, and ideas. 



I also thank the many other members of the 

 California Fish and Game Department and in- 

 terested Salton Sea sportsmen and merchants 



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