The effectiveness of the pituitary preparations 

 was evaluated by monitoring the gonosomatic 

 index (GSI), ovulation, success of egg fertilization, 

 and hatching success. Hormones were prepared on 

 the day of injection, and dosages were established 

 by the weight of each individual fish. A saline solu- 

 tion of isotonic sodium chloride was used as a car- 

 rier. All injections were administered (2-cm'^ 

 syringe, 20 gage 3.85-cm needle) intramuscularly 

 into the back below the dorsal fin. Inserting and 

 withdrawing the needle slowly aided in retaining 

 most of the fluid in the flesh. After injection, the 

 flesh of the fish was massaged to diffuse the fluid 

 into the muscles. 



Sexually mature fish were hand stripped and 

 the eggs fertilized in a polyethylene pan. Several 

 thousand eggs were collected at each spawning, 

 and the sperm of two males was used to fertilize 

 the eggs from each female. Yellowtail flounder are 

 nonsynchronous spawners (Bigelow and 

 Schroeder 1953), and multiple spawnings occur- 

 red among most induced fish. The fecundity of 

 yellowtail flounder increases with age and body 

 length, and an individual female may yield from 

 350,000 to more than 4,000,000 eggs during the 

 spawning season (Pitt 1971). 



The state of ova maturation of the experimental 

 fish was observed at the start and termination of 

 each experiment. Before injecting, a polyethylene 

 cannula was inserted into the oviduct and oocyte 

 samples were orally withdrawn. The oogenesis of 

 oocytes was divided by microscopic observation 

 into three general histological stages: 



Stage I - the primary oocyte stage, oocytes con- 

 tained cytoplasmic vacuoles and mea- 

 sured between 0.1 and 0.25 mm. 



Stage II - the yolk globule stage, cytoplasm of 

 oocytes was filled with dense yolk 

 granules and measured up to 0.6 mm. 



Stage III - ripe stage, hyaline oocytes present 

 and measured 0.75-1.00 mm in size. 



Fertilized eggs were incubated in static, aer- 

 ated, black-sided aquaria that had been inocu- 



lated with the green algae Dunaliella sp. A single 

 application of penicillin (25 international units 

 iIU]/ml) and streptomycin (0.02 mg/ml) at the con- 

 centration of 50 mg/1 was effective in controlling 

 bacterial contamination of the aquaria in almost 

 all cases. 



Three series of experiments were undertaken to 

 determine the effectiveness of the hormone injec- 

 tions (Table 1). The first trial was conducted in 

 winter 1975 to determine if induced spawning 

 would occur at low winter water temperatures. 

 The second and third were conducted in the 

 springs of 1976-77 and coincided with the yellow- 

 tail flounder's natural spawning season. 



Hormone dosage levels of 2, 5, and 10 mg/kg fish 

 and frequency of injecting were dictated by previ- 

 ous successful results obtained with the summer 

 flounder, Paralichthys dentatus, (Smigielski 

 1975a) and winter flounder, Pseudopleuronectes 

 americanus, (Smigielski 1975b). After each trial 

 the female fish were killed and reweighed, the 

 ovaries were examined, and gonosomatic indices 

 were recorded. Prior to receiving hormone injec- 

 tions, all the female test fish in the first trial were 

 in Stage I of oocyte oogenesis, and most females 

 prior to the second and third trials were in Stage 

 II. Males were not injected in the second and third 

 trials because they were sexually ripe. 



Rfsults and Discussion 



First Trial 



In the first trial (Table 1), most females in the 

 group receiving 10 daily injections of 2 mg pitui- 

 tary were refractory with low GSI values (7-13%). 

 One fish hydrated but did not ovulate, and a small 

 number of Stage II ova were found in the ovaries. 

 Hydration is an increase in total body weight. The 

 weight gain is due mostly to water intake and is 

 reflected by higher GSI values as most of the water 

 appears to go into the gonads. Excessive hydration 

 is manifested by grossly bloated fish which in some 

 instances can hydrate to the point of death without 

 ovulating. 



Table l. — Hormone dosages, water temperatures, and number of yellowtail flounder in each trial. 



932 



