FISHERY BULLETIN: VOL. 69, NO. 1 



Table 1. — Total weight, GSI (gonad weight/body weight 

 X 100) and percent water in testis of male Bairdiella 

 icistia injected with various dosages of salmon pituitary. 



Treatment ,^|,^„ ^ jp, ^^^^^ ^ jp, j^^^,^ _^ sp, 



Control; 



0.01 ml/9 67.96 ± 13.38 7.03 ± 1.13 85,2 ± 1.08 5 



sesame oil 



Salmon 



pitu.tory 59.97 ± 11.67 5.25 :t 1.61 86.0 ±1.20 5 



0.005 mg/g 



Salmon 



pituitary 59.34 ± 6:99 5.53 ± 1.74 85.8 ± 1.14 5 



0.01 mg/g 



was not comparable to hydration in females and 

 was not further pursued. Possibly stronger 

 doses of pituitary would give a positive response. 

 The time scale and extent of the seminal hydra- 

 tion and thinning response might be useful in 

 assessing the effect of various hormones and 

 dosage relationships where female fish are at 

 a premium and males would otherwise be in ex- 

 cess. This bioassay technique has been used for 

 salmon pituitary gonadotropin (Yamazaki and 

 Donaldson, 1968a, 1968b). 



were captured in October 1969, placed in 14° C 

 or 22° C water on a 16L or 8L photoperiod, and 

 given an abundance of food (Oregon moist chow 

 and chopped squid). These fish grew to ma- 

 turity in a little less than 4 months at 16L:8D 

 and 22° C (Table 2, group 1) . Similar fish kept 

 on 8L:16D at 14° C did not grow as rapidly as 

 warm-water fish and did not mature under these 

 conditions (compare groups 1 and 2, Table 2, 16- 

 11-70). The lack of maturity was not due to 

 the slower growth rate of the fish kept in cold 

 water, as Salton Sea fish of lower average weight 

 showed higher GSI values at their capture dur- 

 ing the spawning season (Table 2, group 3). 

 Short days, therefore, inhibited the maturation 

 process. These same fish (Table 2, group 2) did 

 mature rapidly, in 2 months, when the water 

 temperature was increased to 22° C along with 

 increased photoperiod. Young fish in their first 

 year do not have as high a percentage of gonad as 

 fish older than 1 year (Table 2, groups 3 and 4) . 

 Mature fish. — A sample of fish more than 1 

 year old, captured in November 1968, 6 months 



GONAD MATURATION (FEMALES) 



Seasonal Maturation Cycle in the Salton Sea 



A series of croaker samples was taken from 

 the Salton Sea at monthly or more frequent 

 intervals during the year. GSI values were less 

 than 2 % from January to mid-March 1969, 

 prior to spawning, and less than 1 "Jr from mid- 

 June to December 1969, following spawning. 

 From mid-March to mid-April, the mean GSI 

 increased rapidly from 2 '}i to 10 ';> and reached 

 a high of 12 % in mid-May (Fig. 1); at this 

 time, individual females were caught with GSI's 

 of more than 17 %. Peak spawning in the 

 Salton Sea was observed in May and early June 

 in 1969. Le.ss frequent sampling and obser- 

 vations confirmed a similar pattern of events 

 in 1970. In the years 19.5.5, 1956, and 19.57, 

 Whitney (1961) found that the peak abundance 

 of croaker eggs and larvae in the Salton Sea fell 

 in middle and late May. 



Laboratory Cycle and Effects of Photoperiod, 

 Water Temperature, and Food 



Immature fish. — Young-of-the-year croakers 



Salton Sea Bairdiella 1968- 



A M J 

 MONTH 



Figure 1. — Seasonal change in GSI of female Bairdiella 

 icistia captured in the Salton Sea. Hori7.ontal line in- 

 dicates the mean GSI value; vertical line indicates 

 range; on either side of the mean, open bar indicates 

 the standard deviation, and closed bar two standard er- 

 rors of the mean of each sample. The number of fish 

 sampled is given in parentheses. Horizontal dashed 

 line indicates 5 % GSI for comparison w-ith laboratory 

 fish (Fig. 2). 



164 



