FISHERY BULLETIN: VOL. 69, NO. 1 



example of a marine fish showing similar deter- 

 mination (Walker, 1952). 



The necessity of working with the reproduc- 

 tive products of one species only during its 

 normal spawning season is one of the major 

 obstacles faced by experimentalists and fish 

 culturists. Most species of temperate and high 

 latitudes show rather well-defined, short spawn- 

 ing seasons, probably related to the annual cycle 

 of day length, temperature, and associated pro- 

 ductivity. This seasonality generally means 

 that experimental work proceeds at a hectic pace 

 for a short time and then must be dropped or 

 switched to another species available in breed- 

 ing condition. This causes numerous difficulties, 

 delays, and expenses for both research and re- 

 searcher. The answer to this problem is to 

 artificially induce maturation and spawning 

 under controlled laboratory conditions. 



To my knowledge, artificial gonad maturation 

 under controlled conditions of light and temper- 

 ature, hormone-induced spawning, and labora- 

 tory rearing of the fragile larvae through meta- 

 morphosis have not been accomplished for any 

 single marine fish prior to this time. Pompano 

 have been spawned with hormones, but the fer- 

 tilized eggs did not hatch (Finucane, 1970). A 

 euryhaline form, Fundulus heteroclitiis, has been 

 spawned with pituitary extract (Joseph and 

 Saksena, 1966) ; however, only mature fish re- 

 cently obtained from their natural environment 

 were used. 



Protocols for hormone-induced spawning of 

 numerous species of freshwater fishes is well 

 established (Dodd, 1955; Fontenele, 1955; Clem- 

 ens and Sneed, 1962). A useful review of liter- 

 ature on the eflfects of hormones in fishes (Pick- 

 ford and Atz, 1957) has been updated with a 

 comprehensive, annotated bibliography (Atz and 

 Pickford, 1964), and a timely review of various 

 aspects of reproductive physiology of fishes is 

 also available (Hoar and Randall, 1969, 1970). 



Hormone-induced spawning is an accepted 

 part of several commercial fish culture ventures 

 and will be used in many more when techniques 

 become reliably standardized for various spe- 

 cies. Brazilians pioneered the use of hormones 

 in spawning carp, while in Russia, where hydro- 



electric dams block the spawning migrations of 

 sturgeons and salmonids, hormone-induced 

 spawning has been practiced for many years 

 (Atz and Pickford, 1959) . In India, carps spawn 

 naturally in flowing streams but must be in- 

 jected with conspecific pituitaries before they 

 will spawn in ponds (Chaudhuri, 1960; Das and 

 Khan, 1962). Catfish respond to similar treat- 

 ment (Sundararaj and Goswami, 1968). In the 

 United States, several freshwater and anadro- 

 mous species are spawned with hormones (Ball 

 and Bacon, 1954; Clemens and Sneed, 1962; 

 Stevens, 1966). 



My investigation focused on the use of hor- 

 mones in inducing maturation and spawning of 

 the gulf croaker, Bairdiella icistia (Jordan and 

 Gilbert) , both for the specific purpose of obtain- 

 ing eggs for physiological studies of salinity tol- 

 erance and for the more general purpose of 

 studying factors which influence spawning in 

 marine fishes. Once success had been achieved 

 in spawning fish under controlled laboratory 

 conditions, the influences of biological and phys- 

 ical factors on the spawning process were ex- 

 amined in detail. 



THE SALTON SEA FISHERY 



The Salton Sea is a large, saline, inland lake 

 in the lower desert of southern California. The 

 present body of water was formed when the 

 flood waters of the Colorado and Gila Rivers 

 broke through irrigation dikes in 1905 and 

 poured into the then dry Salton Sink. The ir- 

 rigation canals were repaired and the water 

 again brought under control in 1907. Subse- 

 quently, the Salton Sea was declared an agri- 

 cultural sump for the deposition of large quanti- 

 ties of irrigation waste water. This water 

 leached large quantities of salt out of the sur- 

 rounding agricultural land and carried it into 

 the sea. Consequently, over the years the sa- 

 linity gradually increased. Short-term fluctu- 

 ations occurred — reflecting changes in inflow, 

 annual rainfall, surface area, temperature, and 

 evaporation. The salinity of the Salton Sea in 

 1970 is about 37 %o. 



During the period 1950-56, when the salinity 

 of the Salton Sea approximated that of the ocean, 



158 



