FISHERY BULLETIN: VOL. 69, NO, 1 



in a little over 1 day following injection under 

 laboratory conditions. In croakers, the total 

 water uptake is reflected primarily in increased 

 gonad weight and may amount to more than a 

 10 % increase in total body weight. A detailed 

 study of the gonadal hydration of carp, Cyprinus 

 carpio, and goldfish, Carasshis aurahis, following 

 injections of carp pituitary extracts showed a 

 similar pattern of water movement into the go- 

 nad with respect to time (Clemens and Grant, 

 1964). These authors measured the increased 

 water content of the gonad following injection 

 and found that, in the case of males, the peak 

 of seminal fluidity was 24 hr after a single ip 

 injection. A similar response was observed 

 with im injection. Goldfish females injected 

 with 10 mg/g carp pituitary extract showed sim- 

 ilar responses, increasing gonad water by up 

 to 7.2 % over carrier-injected controls. Un- 

 fortunately, the changes they describe are in the 

 relative water content of gonads and various 

 other tissues including blood, and no mention 

 is made of any increase in total body weight re- 

 sulting from water taken up from the external 

 medium. 



Hydration under laboratory conditions results 

 in a grossly distorted appearance in females, 

 the abdominal cavity becoming bloated several 

 hours prior to spawning. In the Salton Sea, fe- 

 males appear plump but never grossly enlarged 

 at spawning. It is possible that naturally 

 spawning females hydrate and ovulate fre- 

 quently but in small amounts over the course 

 of the breeding season and that the laboratory 

 fish show the maximum hydration and ovulatory 

 response because of unnatural overstimulation 

 with the injection of salmon pituitary. Use of 

 10 mg carp pituitary and 100 lU HCG caused 

 an equally strong hydration response, but gen- 

 erally this did not culminate in ovulation when 

 these preparations were used alone. A dose 

 threshold for response was indicated by the in- 

 ability of 1 to 5 mg of carp pituitary to cause 

 hydration. With 100 lU HCG, continued hy- 

 dration without ovulation evidently overstressed 

 the fish and led to their eventual death. On 

 the contrary, PMS gave somewhat variable re- 

 sults, but appeared to have less effect on gonad 



hydration while, at the same time, proving to be 

 a potent ovulating agent. Subthreshold doses 

 of salmon pituitary do not appear to cause hy- 

 dration, but a sequence of injections given at 

 daily intervals will eventually lead to ovulation 

 of small quantities of eggs. This may reflect 

 the response of exceptionally ripe eggs which are 

 able to hydrate and ovulate. 



Thresholds of GSI (above 5 %), water tem- 

 perature (between 17° and 22° C), and hormone 

 dose (e.g., 1 mg or more of salmon pituitary 

 for 50- to 100-g fish) exist, and if any one of 

 these factors is below its threshold, hydration 

 does not occur. 



OVULATION 



Ovulation in croakers is a rapid process, 

 taking 1 to 2 hr for completion when induced 

 with hormones in the laboratory. The period 

 between injection and spawning includes the 

 hydration phase and culminates in ovulation at 

 about 30 hr post-injection. Stevens (1966) 

 found a similar 30-hr latent period for fully 

 mature striped bass, Roccus saxatilis. Clemens 

 and Sneed (1962) found a shorter latent period 

 of 15 hr for goldfish. Fontenele (1955) gave 

 injections to several Brazilian fish species at 6- 

 hr intervals. He stated that spawning usually 

 occurred just prior to the 5th injection (i.e., 

 close to 30 hr after the first injection), although 

 in most cases the fish were allowed to spawn 

 naturally in ponds and were not tested by strip- 

 ping. Indian carp are also allowed to spawn 

 naturally in ponds after injection. Chaudhuri 

 (1960) states that spawning may come 6 to 8 

 hr after the first injection of very mature fish; 

 if a second injection is necessary, the total 

 elapsed time may be 14 to 18 hr. It would ap- 

 pear that in most recorded cases (see above 

 and Pickford and Atz, 1957, Table 46) hormone 

 injection will bring about final maturation and 

 spawning within 1 to 2 days if the gonads are 

 fully mature. In only a few cases (e.g., Joseph 

 and Saksena, 1966) have longer series of in- 

 jections been successfully used to produce viable 

 eggs. 



A constant time period for spawning latency 

 was found to hold for croakers used in this 

 study. When GSI, water temperature, and hor- 



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