FISHERY BULLETIN: VOL. 73, NO. 1 



2 3 4 



TIME (minutes) 



Figure 3. — Spermatozoan activity in four salinities as a func- 

 tion of time after hydration. The activity levels are described in 

 the text. 



sperm was the same as when hydration was car- 

 ried out underneath a cover slip, indicating that 

 the high concentration of spermatozoa in the lat- 

 ter case did not seriously affect the level or dura- 

 tion of their activity. 



Maturity of Spawning Fish 



Examination of many fish during this project 

 showed that 500 fj.Tn was approximately the max- 

 imum diameter attained by oocytes in bairdiella 

 before gonadal hydration. During hydration, 

 which occurs in the laboratory only after an injec- 

 tion of gonadotropic hormone, the accession of 

 water swells the eggs to 700 iimor more, the size 

 at spawning. Ovarian biopsies showed that the 

 two female fish used to supply eggs in the Series A 

 experiments had oocjd^es as large as 500 jjun before 

 injection. The ooc3d;e size-frequency distributions 

 for the fish used in Series B (Figure 4) also showed 

 maximum diameters of about 500 mn, and there 

 were modes at 420 to 455 /am for the first fish and 

 385 to 455 fim for the second in Series B. 



The much poorer fertilization and hatching suc- 

 cess in Series A (see below) indicates that max- 

 imum oocyte diameter is not necessarily a good 

 index of readiness for spawning. By this method it 

 is impossible to tell whether there is a mode at the 

 large end of the size-frequency distribution, as is 

 characteristic of fish which are ready to spawn. 

 The fish used to supply eggs in Series A were 

 probably captured after the peak of spawning in 

 the Salton Sea and their gonads at that time were 



30 



>- 20 

 O 



z 



UJ 



o 



^ '0 



1 



ii 



_^. 





L 



175 2 10 245 280 315 350 385 420 455 490 

 OOCYTE DIAMETER dim) 



30 r 



>■ 20 

 o 



3 

 a 



liJ 10 



cr 



I 



l« 



M 





I 



175 210 245 280 315 350 385 420 455 490 

 OOCYTE DIAMETER (pm) 



Figure 4. — Oocyte size-frequency distributions, based on 

 ovarian biopsies, from fish used in Series B experiments, a) fish 

 spawned on 25 November 1971, b) fish spawned on 3 December 

 1971. 



probably either partly spent or beginning to be 

 resorbed (see Haydock 1971). It was hoped that 

 subsequent exposure to long days would induce 

 ovarian recrudescence, but instead this treatment 

 over a period of 2.5 mo apparently maintained the 

 gonads at a suboptimal state of maturity or al- 

 lowed them to regress even further (see Haydock 

 1971). A postspawning refractory period (Har- 

 rington 1959; Sehgal and Sundararaj 1970) may 

 exist in bairdiella, but it cannot be very pro- 

 nounced, since not only were eggs obtained from 

 these fish after hormone injections in August and 

 September, but at least 60% of the eggs could be 

 fertilized under optimum conditions (see below). 

 The fish used in Series B had completely regressed 

 gonads when they were first exposed to long days 

 in July 1971. By November 1971 or earlier they 

 had developed ovaries capable of producing a large 

 proportion of viable eggs, showing as much as 90% 

 fertilization. 



Fertilization 



Although fertilization did take place at a salin- 

 ity of 15%o, it was completely blocked at 10%o 

 (Table 2). In order to examine this phenomenon 

 further, unfertilized eggs were placed in 10%o 

 water for various periods of time and then trans- 



6 



