MAY: EFFECTS ON BAIRDIELLA ICISTIA 



from a short photoperiod to a 16L:8D photo period 

 between 25 June and 10 July 1971. Half of these 

 fish were transferred gradually to 15%o and al- 

 lowed to mature in that salinity as described 

 below, while the other half were kept in sea water 

 (approximately 33%o) and used to supply eggs for 

 the Series B experiments. Prior to these spawn- 

 ings, ovarian biopsies were taken and oocjrte size- 

 frequency distributions determined to assure that 

 the fish were fully mature. 



Acclimation of Spawning Fish 

 to Low Salinity 



These fish came from the same collection as 

 those used to supply eggs in the Series B experi- 

 ments and were brought to maturity simultane- 

 ously with them. The salinity was lowered to 

 15%o over a period of 8 days by mixing seawater 

 with an increasing proportion of fresh water. The 

 day length was then increased from 9 to 16 h in 

 30-min increments, and the temperature was 

 raised from 16° to 22°C over the same period (Fig- 

 ure 2). The tap water had been dechlorinated by 

 passage through a commercial charcoal filter, and 

 the mixed tap water and seawater flowed through 

 the fish tank at 1 ,000 liters per hour (the same flow 

 rate was maintained in the tank receiving 

 straight seawater). Salinity was monitored daily 

 in the seawater and low-salinity tanks. Variations 

 were relatively slight during the period of gonadal 

 maturation, monthly means ranging from 32.7 



3 16 



I 



uj 10 



35 



30 



15 - 



, • • '^^ — TemperQtu 





Sahnity- 



° o o 



-I 1 I I I I L. 



J i I \ L 



24 O 

 - 22 lij 

 20 3 



18 2 



U 

 16 Q- 



2 



8 10 12 14 16 18 20 22 24 26 28 30 2 4 6 8 10 12 14 

 ^ JUNE 'I JULY 1 



Figure 2. — Day length, temperature, and salinity during tran- 

 sition period, when fish were transferred to low-salinity water, 

 warm temperatures, and long days. 



to 33.3%o in the seawater tank and from 15.2 to 

 15.7°/oo in the low-salinity tank. 



Female fish living at 15%o were injected with 

 PMS on 25 October, 8 November, and 16 

 November 1971. Eggs were fertilized (with sperm 

 from males also acclimated to 15"/oo) and incu- 

 bated as described above, at salinities of 10, 15, 

 20, 30, 40, 45, and 50%o. The temperature was 

 24.0°±0.2°C in all experiments with eggs from 

 fish acclimated to low salinity. Hatched larvae 

 were kept in 400-ml beakers at their original 

 salinity to determine the percentage surviving 

 to yolk exhaustion. The activity of spermatozoa 

 from fish acclimated to 15%o was assessed at 

 various salinities as described above. 



RESULTS 



Spermatozoan Activity 



Bairdiella spermatozoa measured 40 ^m in 

 total length, the head being about 2.5 Mm long. 

 In distilled water and dechlorinated tap water, 

 spermatozoa showed at most only slight move- 

 ment, usually in the form of very slow undulations 

 which lasted at least 10 min. After approximately 

 1 min, the heads of many of these spermatozoa 

 seemed to acquire bright rings, which an oil- 

 immersion lens revealed to be the tail curled 

 around the head, still undulating slowly. 



Bairdiella spermatozoa became activated im- 

 mediately upon contact with seawater (Haydock 

 1971), and the intensity of activity varied with 

 salinity and time after initial contact with water. 

 Spermatozoa were most active at the higher 

 salinities but remained active longest at the lower 

 salinities. At 10 and 15%o, a small smount of ac- 

 tivity remained even as long as 10 min after 

 hydration, but at 10%o spermatozoa seldom 

 showed activity above level 3 and at 15%o they 

 only rarely and briefly attained level 5 (Figure 3). 

 At 25%o all activity ceased by 4 min after hydra- 

 tion, and at 35%o no activity was usually seen 

 after 3 min. At 45 and 55"/oo, activity had com- 

 pletely stopped by 1.5 min after hydration. On 

 rare occasions, at salinities between 15 and 55%o, 

 slow undulations of some spermatozoa were ob- 

 served after other movements had ceased. No dif- 

 ference was noted between spermatozoan activity 

 in seawater and in Salton Sea water, nor between 

 the activity of spermatozoa from fish acclimated to 

 a salinity of 15%o and from those kept at 33%o. 

 Spermatozoan activity in dilute suspensions of 



