HAYDOCK: GONAD MATURATION OF GULF CROAKER 



the California Department of Fish and Game 

 transplanted a variety of fishes from the Gulf 

 of California with the intent of establishing 

 a productive sport fishery. The present fishery 

 stems from the descendants of a total original 

 introduction of 57 gulf croaker, 67 sargo, Anis- 

 otremus davidsoni, and 100 to 200 orangemouth 

 corvina, Cynoscion xanthulus, transplanted to 

 Salton Sea in 1951-52 (Walker, 1961; Whitney, 

 1967). The fishes thrived and developed large 

 populations in the simple, man-made ecosystem, 

 but increasing salinity now threatens the con- 

 tinuing existence of the famous fishery. 



The Salton Sea Investigations was a joint Fed- 

 eral-State pi-oject whose overall goal was to pre- 

 dict a target salinity at which a water quality 

 control project could be aimed that would not 

 be detrimental to the present highly esteemed 

 fishery. Engineering studies had suggested a 

 method by which the salinity of the Salton Sea 

 could be controlled, but the maximum permis- 

 sible salinity levels still had to be established 

 on the basis of biological information. Other 

 sciaenid species live in the Gulf of Mexico in a 

 wide range of salinities up to 75 ^r, but it is 

 considered unlikely that spawning occurs in ex- 

 tremely high salinities or that the larvae could 

 tolerate such osmotic stress (Gunter, 1967; 

 Hedgpeth, 1959). 



To attain our goal in the short time available, 

 we have developed all of the necessary tech- 

 niques for spawning Salton Sea fishes under 

 controlled laboratory conditions. These tech- 

 niques have proved successful for obtaining 

 viable spawn for the necessary salinity tolerance 

 studies of both croaker and sargo.' I had ori- 

 ginally assumed that the close relationship of 

 gulf croaker to corvina, both of the family 

 Sciaenidae, would make it possible to apply 

 croaker spawning techniques directly to the cor- 

 vina. However, the carnivorous nature of cor- 

 vina and the general difliculty of handling this 

 powerful fish in the laboratory demanded special 

 feeding and holding techniques and precluded 



successful laboratory spawning. Hormone-in- 

 duced spawning has been achieved in our lab- 

 oratory with other mature marine fishes, includ- 

 ing Eucinostomus sp. (family Gerridae), Geny- 

 ovemus lineatus (Sciaenidae), and sargo (Hae- 

 mulidae). The techniques developed for in- 

 ducing spawning with hormones in gulf croakers 

 may thus have general applicability. 



METHODS 



CAPTURE, TRANSPORT, CARE, AND 

 HANDLING OF FISH 



Two year classes of gulf croakers were cap- 

 tured with a 60-m beach seine in May and Oc- 

 tober 1969. The first sample consisted of ma- 

 ture fish, 1 year old, and the second of young-of- 

 the-year fish which were subsequently matured 

 under controlled photoperiod and temperature 

 conditions in the laboratory. The fish were 

 captured on sandy beaches north of the U.S. 

 Navy Base and north of the Salton Bay Marina, 

 both on the west side of the Salton Sea. A beach 

 seine is the most dependable method for captur- 

 ing large numbers of these fish in good condition, 

 e.Kcept in midsummer and late winter, when 

 fish are unavailable near shore. 



The fish were transported to La Jolla, Calif., 

 in a 500-liter tank equipped with aeration and 

 filtration devices. In transport, and for several 

 subsequent days in the laboratory, the fish were 

 treated with Furacin antibiotic' at an initial con- 

 centration of 250 mg/3.8 liter. Several early 

 failures showed that careful handling, high 

 standards of water quality, and, especially, anti- 

 biotic treatment are all essential to high sur- 

 vival rates of Salton Sea fishes after capture. 



In the laboratory, the fish were held in 2,000- 

 liter rectangular tanks (2 m x 1 m X 1 m deep) 

 supplied continuously from the seawater supply 

 of the Fishery-Oceanography Center in La Jolla. 

 A general description of this extraordinary fa- 

 cility is available (Lasker and Vlymen, 1969). 

 A water temperature of 22 ± 1° C was main- 



' Reuben Lasker and Richard R. Tenaza. 1968. 

 Salton Sea fish larvae investigation progress report: 

 techniques and preliminary experiments on osmotic stress 

 (spring-summer 1968) . Inland Fisheries .Administrative 

 Report No. 68-7, Oct. 1968, (Unpublished). 



' Sharpe and Vejar, Los Angeles, Calif. Use of trade 

 names is merely to facilitate descriptions; no endorse- 

 ment is implied. 



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