MAY: EFFECTS ON BAIRDIELLA ICISTIA 



Table 2. — Percentage fertilization at various combinations of 

 temperature and salinity in Series A and B. 



Temperature 



(°C) 



Salinity 



(°/oo) 



Percentage fertilization 



Table 4. — Survival and hatching of fertilized eggs transferred 

 from 20''/oo to 10%o at various stages. Eggs were incubated in 

 20-ml petri dishes. The stages are described in Table 6. 



Series A 



Series B 



18 



21 



24 



27 



30 



10 

 20 

 30 

 40 

 50 



15 

 25 

 35 

 45 

 55 



10 

 20 

 30 

 40 

 50 



15 

 25 

 35 

 45 

 55 



10 

 20 

 30 

 40 

 50 





 14.5 

 48.5 

 24.4 

 14.8 



13.4 

 43.5 

 35.8 

 38.8 

 1.9 







63.1 



43.2 



7.4 



5.7 



33.7 

 52.6 

 60.1 

 16.8 

 





 48.7 

 15.3 



2.7 









 28.9 

 81.6 

 87.5 

 41.6 



18.4 



69.9 

 49.4 

 59.9 

 52.5 





 62.3 

 87.8 

 81.3 

 50.8 



30.3 

 77.2 

 76.7 

 82.0 

 67.4 





 74.6 

 89.8 

 68.7 

 23.1 



ferred to 20%o and immediately exposed to sperm. 

 The results (Table 3) showed that 10%o water did 

 not render the eggs infertile: even after 20 min at 

 10%o, a large proportion of the eggs could be fer- 

 tilized at 20%o and develop to hatching, although 

 there was no fertilization in controls kept at 10%o . 

 It was also found that eggs fertilized at 20%o could 

 be transferred to 10%o and develop to hatching 

 (Table 4). Thus the actual process of fertilization 

 was somehow blocked at 10%o. 



In Series A, fertilization was much more sensi- 

 tive to high salinities and there seemed to be a 

 greater temperature-salinity interaction than in 

 Series B, with fertilization being more successful 

 at high salinities when the temperature was low 

 (Table 2). In Series B, at salinities above 10%o, 



Table 3. — Effect of exposure to IC/oo water for various periods of 

 time on fertilizability of bairdiella eggs at 20''/oo . At each time 

 interval, between 200 and 400 eggs were transferred from 10 to 

 20''/oo, exposed to sperm, and later examined for fertilization. 

 Thirty fertilized eggs from each group were followed until hatch- 

 ing. 



fertilization was in nearly all cases over 50% , the 

 few exceptions being at low temperature/low sa- 

 linity and high temperature/high salinity com- 

 binations. A maximum of 89.8% fertihzation was 

 observed at 30°C-30%o in Series B. The thermal 

 limits for fertilization in Series B were evidently 

 beyond the range tested (18°-30°C). 



Normal Development 



It will be helpful to outline the normal pattern of 

 development of bairdiella eggs before discussing 

 alterations in this pattern induced by various 

 combinations of temperature and salinity. Newly 

 spawned bairdiella eggs are approximately 725 

 jum in diameter and contain an oil globule with a 

 diameter of about 18 pm. Occasionally there are 

 two or three smaller oil globules instead of a single 

 one. Like most pelagic eggs, bairdiella eggs float 

 with the animal pole downward. The development 

 o^Bairdiella icistia eggs (Table 5, Figure 5) follows 

 the pattern typical for small pelagic fish eggs and 

 is not greatly different from that of 5. chrysura as 

 described by Kuntz (1915). Ahlstrom's numerical 

 designation of developmental stages (Ahlstrom 

 1943) has been adopted here (Table 5), although 

 some slight modifications of his scheme were 

 necessary, and some of the stages have been 

 broken down into substages. The times required to 

 reach certain stages are listed (Table 5) for eggs at 

 33%o at 25°C, based on observations made during 

 a preliminary experiment in 1970. The newly 

 hatched larvae are approximately 1.7 mm in 

 length (snout to tip of notochord) and in ordinary 

 seawater float upside down near the surface of the 

 water. 



Incubation Time 



The time between fertilization and hatching 

 varied with temperature and with salinity, and 

 the patterns of hatching determined from the sup- 

 plementary containers in Series B are shown in 



