HAYDCXTK: GONAD MATURATION OF GULF CROAKER 



I 





I I I I I 



I I I I I I I I I I I 



060O 1200 



TIME OF INJECTION tPST) 



Figure 3. — Time of injection (Pacific Standard Time) 

 and time of spawning (hours post-injection) in relation 

 to photoperiod. All injections were 1-3 mg salmon pitui- 

 tary extract and all fish produced viable eggs. Solid 

 black bar indicates dark period; dashed line indicates 

 mean time of spawning. 



five fish were injected with 1 mg salmon at a 

 time corresponding with the beginning of the 

 laboratory dark cycle. All these fish spawned 

 24 hr later, indicating a possible enhancement 

 by the normal diurnal cycle of glandular activity. 

 Natural spawning in the Salton Sea is I'elated 

 to the normal diurnal light cycle, with most 

 spawning occurring in the early evening. 



Factors Affecting Ovulation 



It has already been shown that GSI level, 

 hormone dosage and type of hormone are criti- 

 cal interacting factors which must be considered 

 in any spawning eff'ort. Injection of high levels 

 of salmon (5 mg) may possibly assure a more 

 uniform hydration response (see GSI of Table 

 7), but the nonviable eggs which result speak 

 against using more than the minimal dose found 

 to give consistent results. 



The eflfect of temperature on ovulation per se 

 was not studied. Hydration is effectively 

 blocked at temperatures lower than 17° C, but 

 this effect was reversed after 24 hr acclimation 

 at 22° C. In the cases in which this transfer 

 was carried out, a second injection was given 

 24 hr after transfer, and spawning took place 

 approximately 30 hr later. 



As a matter of practical interest, it was found 

 that fish could be injected and spawned twice 

 (tried, successfully, with two fish) or three times 



(one fish) with a period between spawnings of 

 3 to 4 weeks. This is in contrast to the much 

 longer time required for maturation after fish 

 had slowly resorbed their gonads in photoperiod 

 experiments (Fig. 2). Apparently the rapid 

 emptying of the gonad consequent upon hor- 

 monal injection quickly leads to a renewed cycle 

 of egg maturation. 



The direct and indirect effects of various in- 

 jections on the gonad were assessed by biopsy 

 following spawning or the lack of spawning. 

 These qualitative observations are listed in Table 

 10; no attempt is made to interpret these results, 

 except to point out that fish injected with salmon 

 pituitary extract had gonads most closely re- 

 sembling those of naturally spawning fish. 



Table 10. — Appearance of mature Bairdiella icistia 

 ovaries during natural spawning and 30 hr after various 

 hormone injections, and color reaction of fish to 

 injections. 



1. Sollon Sea fish at spawning 



Gonad color white, light yellow or red-orange. Consistency of 

 ■nature gonad is granular with patches of tronsporent eggs which 

 are close to being ovulated or are lying free in the ovarian lumen. 



2. Salmon pituitary extroct 



Gonad color and consistency very close to naturally spawning fish. 

 Mast eggs ovulated and free in lumen. Fish blanch on injection. 



3. Corp pituitary extract 



Gonad color red-orange; few eggs ovulated. In fish given 5 mg 

 dose, blood clots oppeared to be blocking oviducts near vent. 

 Fish blanch on injection. 



4. PMS 



Gonad whitish, translucent; strikingly different from other prepa- 

 rations. Most eggs ovulated and free in lumen. Possibly, greater 

 degree of ovulotion with less hydration makes gonad appear lighter 

 in color. Fish do not blanch on injection. 



5- HCG 



Eggs either not ovulated or partially ovulated; those not ovulated 

 appear as white patches in the ovary. Many vacuoles and dis- 

 persed oil drops appear in eggs. Fish do not blanch on injection. 



6. Oxytocin 



Ovary was very bloody. Eggs white (not hydroted); different 

 sized eggs (mostly large) apparent in ovarian folds. Fish do not 

 blanch on injection. 



7. DOCA 



Fish showed no observable reaction. 



FERTILIZATION 



Relationship ot Egg Viability to the Time 

 of Ovulation 



Shortly before ovulation, eggs could be 

 squeezed from females by applying strong pres- 

 sure to the abdomen, but eggs obtained in this 

 way still had an investiture of blood vessels and 

 ovarian tissue and could not be fertilized. An 

 analysis of viability in relation to the time after 



171 



