FISHERY BULLETIN: VOL. 69, NO. 1 



Table 11. — Fertilization and viability of Bairdiella icistia 

 eggs tested over a 4-hr period following first ovulation. 

 Fish was injected with 1 mg salmon pituitary extract 

 at 0930 l-V-70; first eggs expressed with some difficulty 

 at 1530 2-V-70. 



Time of 

 fertilization 



Development 

 to early 

 tailbud 



Hatching 



ovulation was made in the case of one fish which 

 remained ripe for 4 hr (Table 11). To check 

 for viability, eggs were test-fertilized at hourly 

 intervals following the first sign of ovulation, 

 taken as the earliest time when normal eggs 

 could easily be expressed from the fish by gentle 

 pressure applied to the abdomen. Fertilization 

 and early cleavage remained above 90 '^f up to 

 3 hr post-ovulation. By 4 hr the eggs looked 

 crinkled, opaque, and spotty, and less than 5 % 

 could be fertilized. A further measure of via- 

 bility was made by culturing 100 early cleaving 

 eggs from each batch until hatching. A decrease 

 in hatching success was noted in the eggs ob- 

 tained 2 hr after the initial ovulation, and hatch- 

 ing decreased still further in the 3- and 4-hr 

 post-ovulatory samples. It appears that the 

 maximum grace period for egg-taking is about 

 2 hr. In another experiment I studied eggs from 

 a larger sample of 10 fish determining fertil- 

 ization success as a function of time after ovu- 

 lation; the optimum time for taking eggs was 

 1 hr after the fish first showed signs of running 

 ripeness and gave viable eggs. 



Although eggs rapidly deteriorated when kept 

 in the ovary following hormone-induced ovula- 

 tion, it was found that they retained their ability 

 to be fertilized up to several hours after they 

 were placed in a moist storage chamber. Eggs 

 placed in seawater remained fertile for several 

 minutes; in one case, a few cleaving eggs re- 

 sulted from fertilization carried out after the 

 eggs had been in seawater for 30 min. 



Viability of Sperm 



Although eggs kept in seawater remained 

 viable for several minutes, sperm were no longer 

 able to fertilize eggs 30 sec after the sperm mass 

 had been introduced into seawater. It is thus 

 readily apparent that croaker sperm and eggs 

 should be mixed immediately after the sperm 

 is obtained, in order to achieve maximum fertil- 

 ization. Microscopic examination showed that 

 sperm were immediately activated by addition 

 of water and retained motility for a period of 

 1-5 min. In some tests it was apparent that 

 water from the Salton Sea caused greater ac- 

 tivity for a longer time than water taken from 

 the ocean at La Jolla, Calif., but there was great 

 variability between males, and a proper tech- 

 nique of quantifying this relationship awaits 

 further studies. 



Number of Eggs Obtained by Hormone 

 Treatment 



The number of eggs obtained by hormone in- 

 jection varied between 700 and 1,000 per gram 

 of fish wet weight (Table 12). This provided 

 50,000 to 100,000 eggs for experiments from 

 each fish of 50 to 100 g used in this study. 



Table 12. — Number of eggs obtained from hormone-induced spawning of Bairdiella icistia. 



Indicates volues colculoted from meosured parameter and mean number of eggs per gram counted. 



172 



