MAY: EFFECTS ON BAIRDIELLA ICISTIA 



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 OOCYTE DIAMETER (;jm) 



Figure 14. — Oocyte size-frequency distributions, based on 

 ovarian biopsies, from fish acclimated to IS^/oo. 



Table 10. — Fertilization success for eggs obtained from fish ac- 

 climated to 15%o. 



Salinity 

 (°/oo) 



Percentage fertilization 



10 

 15 

 20 

 30 

 40 

 45 

 50 



Table 11. — Percentage total and viable hatch of fertilized eggs 

 at various salinities for eggs from fish acclimated to 15''/oo. For 

 each fish, there were two replicate groups of eggs at each salin- 

 ity. 



Salinity 



Fish I 



Fish I 



Fish I 



there a significant difference between sexes 

 within each group (Mann- Whitney U test; Siegel 

 1956). 



The fish with poorly developed ovaries (Fish I) 

 became listless and swam in a disoriented manner 

 after the hormone injection; 5 days after spawn- 

 ing, it still spent most of its time resting on its side 

 on the bottom of the tank. At this point the fish 

 was sacrificed and dissected, revealing some large, 

 hydrated eggs with coalesced yolk, 665-735 A^m in 

 diameter, along with many unhydrated eggs still 

 in their follicles, measuring 350 jum in diameter. 

 Eggs obtained from the hormone-induced spawn- 

 ing of this fish showed low fertility, significant 

 numbers being fertilized only at 15 and 20%o, 

 with a maximum of 24.2% fertilized at 20"/oo 

 (Table 10). The hatching success of fertilized eggs 

 was also poor, with a maximum total hatch of 

 44.2% at 20%o (Table 11). A few embryos and 

 larvae produced by this fish displayed various de- 

 grees of cyclopia, a deformity rarely seen in other 

 batches of eggs. 



As expected, the two ripe fish produced much 

 better eggs, with maximum fertilization percent- 



ages of almost 90% (Table 10). Eggs from Fish II 

 had a lower optimum salinity than those from 

 Fish III and were more sensitive to high salinities 

 (Table 10). No fertilization took place at 10%o, as 

 was the case with eggs from fish living at 33%o. 



Hatching at 15, 20, and 30%o was better in eggs 

 from Fish III than in those from Fish II, despite the 

 better fertilization success of the latter at 15 and 

 200/00 (Table 11). Hatching at 40, 45, and 50%o 

 was comparable in the two batches of eggs. Eggs 

 from Fish II hatched more successfully at 15 and 

 20%o than at 30%o, whereas those from Fish III 

 hatched equally well at 15, 20, and 30%o. The 

 incidence of postmature unhatched eggs was simi- 

 lar to that in eggs from Series A and Series B, with 

 most appearing at 15 and 20%o, few at 30%o, and 

 very few or none above 30%o. 



The hatching success at various salinities (20, 

 30, 40, and 50%o) of the best batch of eggs from 

 fish living at 15%o (i.e., from Fish III) was com- 

 pared with that of the best batch of eggs from fish 

 at 33%o (Series B) at the same temperature (24°C) 

 and salinities, by ANOVA (an arcsin-square root 

 transformation was applied to the percentages). 



17 



