FISHERY BULLETIN: VOL. 73, NO. 1 



Neither total nor viable hatching success differed 

 significantly between the two groups. Therefore, 

 acclimation of spawning fish to a low salinity did 

 not affect the salinity tolerance of the eggs in any 

 detectable way. Effects of acclimation salinity on 

 egg size and buoyancy will be discussed elsewhere 

 (May in preparation). 



DISCUSSION 



Fertilization and early development in Bair- 

 diella icistia are stenothermal and stenohaline 

 processes. The approximate limits for successful 

 development, from fertilization to yolk exhaus- 

 tion, are 20° to 28°C and 15 to 40%o, although a 

 certain interaction of the two factors is apparent, 

 development being more successful at the higher 

 salinities when the temperature is relatively low, 

 and at the higher temperatures when the salinity 

 is relatively low. The limits within which success- 

 ful reproduction can take place are defined by the 

 most sensitive stages and events in development. 

 The lower limit of salinity for bairdiella reproduc- 

 tion is defined by fertilization, since eggs cannot 

 be fertilized at 10%o or below, even though eggs 

 fertilized at a higher salinity will develop at 10%o . 

 However, the lowest salinity at which eggs remain 

 buoyant may in some cases determine the lower 

 salinity threshold for successful reproduction 

 (May 1972). The upper salinity limit, and both the 

 upper and the lower limits of temperature, are 

 defined by the abilities of the embryos to develop. 

 Fertilization is successful at 18°C but develop- 

 ment is not; likewise, fertilization does take place 

 at 30°C, and at salinities of 45%o and above, but 

 the hatching of viable larvae is greatly curtailed. 



Fertilization in bairdiella is more limited by 

 salinity than temperature over the ranges 

 studied. The complete block to fertilization which 

 occurs at 10%o may be related to an inability of 

 spermatozoa to function properly at this salinity. 

 Although the egg itself seems to be unharmed by 

 water of IC/oo, at this salinity spermatozoa never 

 attain the high intensity of activity that they do at 

 higher salinities. At 15%o, where spermatozoan 

 activity is more intense than at 10%o but less 

 intense than at higher salinities, fertilization oc- 

 curs but is poorer than at higher salinities. Fairly 

 high salinities seem to aid fertilization: the calcu- 

 lated optimum salinities for fertilization were 

 higher than the optima for hatching in both Series 

 A and Series B. It is possible that low calcium 

 levels at low salinities inhibit the activity of 



18 



spermatozoa (Yanagimachi and Kanoh 1953). In 

 general, the greater the intensity of spermatozoan 

 activity, the shorter is the overall duration of ac- 

 tivity (Figure 3). Thus a shortlived but extremely 

 high level of spermatozoan activity may be neces- 

 sary for fertilization in bairdiella, perhaps be- 

 cause penetration of the micropyle requires a con- 

 siderable expenditure of energy on the part of the 

 spermatozoa. This implies that the actual process 

 of fertilization takes place during the first few 

 seconds after hydration of the sperm, when sper- 

 matozoan activity is maximal. Haydock ( 1971) re- 

 ports that bairdiella spermatozoa are no longer 

 able to fertilize eggs 30 s after sperm hydration. 

 In such a situation, experimental technique could 

 have a marked influence on the success of artificial 

 fertilization, since a delay of a few seconds be- 

 tween hydration of the sperm and contact of the 

 sperm with eggs could significantly reduce the 

 percentage of eggs which become fertilized. A 

 technical problem of this sort may explain the 

 puzzling differences in fertilization success be- 

 tween eggs from Fishes II and III, acclimated to 

 150/00 (Table 10). 



Several previous investigations of salinity ef- 

 fects on spermatozoan activity in other fishes pro- 

 vide interesting contrasts with the present 

 results. Ellis and Jones (1939) found that sper- 

 matozoa of Atlantic salmon, Salmo salar, a fish 

 which spawns in fresh water, were active for over 

 180 min in seawater diluted to 15 and 20% and 

 that the duration of activity dropped off sharply 

 above and below these salinities. Working with 

 the longjaw mudsucker, Gillichthys mirabilis, 

 Weisel (1948) observed that spermatozoa showed 

 only feeble activity in seawater diluted to 17-24%, 

 but activity was intense in 25% seawater and 

 above; the duration of spermatozoan activity was 

 maximal (over 50 h!) in 25% seawater and de- 

 creased at higher salinities, as it did in the case of 

 bairdiella. Yamamoto (1951) found that sper- 

 matozoa of the flounder, Limanda schrenki, were 

 active in normal seawater and in seawater diluted 

 to 50%, but showed no activity (and no fertilizing 

 capability) in 25% seawater. Hines and Yashouv 

 (1971), on the contrary, found that mullet, Mugil 

 capita, spermatozoa exhibited a gradual increase 

 in duration of activity with increasing salinity up 

 to the salinity of normal seawater, rather than a 

 threshold. Dushkina (1973) reported that sper- 

 matozoa of Pacific herring, Clupea harengus 

 pallasi, were most active at higher salinities 

 (17-23"/oo), but remained active longest at the 



