GONAD MATURATION AND HORMONE-INDUCED SPAWNING 

 OF THE GULF CROAKER, Bairdiella icistia' 



Irwin Haydock" 



ABSTRACT 



Successful methods of capture, transport, disease treatment, and laboratory maintenance of the gulf 

 croaker, Bairdiella icistia, are described. Gonad maturation was achieved out of season by the use of 

 appropriate controlled photoperiods, temperatures, and abundant feeding. Mature fish or fish brought 

 to maturity in the laboratory were spawned with suitable hormone injections and the time of spawning 

 could be accurately predicted. Eggs obtained from hormone-induced spawning were normal in all re- 

 spects and the larvae were reared through metamorphosis using rotifers and brine shrimp nauplii as 

 food; thus, the life history of this marine fish can, for the first time, be completed under controlled lab- 

 oratory conditions. The techniques developed for croakers may have application to mariculture, biossay 

 of marine pollution, and in more general research on marine fish reproduction. 



Reproduction in fishes which spawn annually 

 is controlled by the interaction of exogenous and 

 endogenous stimuli, particularly the endocrine 

 activity of the pituitary-gonadal axis which is 

 indirectl.v influenced by environmental factors 

 such as day length and temperature. Against 

 this basic background, which determines the 

 gonadal maturation cycle, the actual spawning 

 act is controlled by neurohumeral and neuro- 

 muscular connections activated by rapidly 

 changing environmental parameters and behav- 

 ioral cues (Liley, 1969; Malven, 1970). This 

 basic reproductive pattern and the lacunae in 

 our understanding of it have recently teen re- 

 viewed in detail (Breder and Rosen, 1966; Hoar, 

 1969). 



Much of the work on reproductive physiology 

 of fishes has been done with freshwater species 

 of interest to aquarists (Wickler, 1966) or ex- 

 perimentalists (New, 1966; Hoar, 1969; Liley, 

 1969). There is, however, no reason to suspect 

 that the basic features of reproduction, eluci- 

 dated with freshwater species convenient to 



' This research was supported, in part, by Federal 

 Aid to Fish Restoration Funds, Dingell-Johnson Project 

 California F-24-R, "Salton Sea Investigations." 



" Formerly, California Department of Fish and Game, 

 Inland Fisheries Branch, Sacramento, Calif. ; present ad- 

 dress: Southern California Coastal Water Research 

 Project, 18045 Lindbrook Drive, Los Angeles, Calif. 

 90024. 



Manuscript received September 1970. 



FISHERY BULLETIN: VOL. 69. NO. 1, 1971. 



maintain, will differ significantly from those of 

 marine forms, which require more elaborate 

 facilities for study. 



Because of increasing demand for fish as a 

 source of protein, as well as for sport and for 

 scientific studies on reproductive success of 

 fishes in generally deteriorating natural environ- 

 ments, there are now intensive and extensive 

 efforts to artificially culture commercially val- 

 uable freshwater species (Hickling, 1962; Hora 

 and Pillay, 1962; Bardach, 1968). Recent in- 

 terest has also focused on mariculture, the culti- 

 vation of marine species. Some success has been 

 achieved in Great Britain (plaice and sole — 

 Shelbourne, 1964 and 1970), Japan (bream and 

 yellowtail — Harada, 1970), and in the United 

 States (pompano — Finucane, 1970). However, 

 all such cultures are started either with young 

 fish caught at sea or with eggs spawned in the 

 sea or stripped from mature fish captured during 

 their normal spawning season. The field work 

 necessitated by this method can be costly and 

 unpredictable, drawbacks which are compounded 

 by the difficulty usually experienced in simul- 

 taneously finding running-ripe fish of both sexes, 

 especially females. These pi-oblems are avoided 

 in the culture of salmonids because of the unique 

 determination of the fish to return to the same 

 place to spawn at a fairly predictable time 

 (Leitritz, 1959). The grunion is a striking 



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