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SALINITY (%o) 



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Figure 13. — Summary of the effects of temperature and salinity 

 on early development of bairdiella. Closed circles identify treat- 

 ment combinations utilized in the experiments, and the numbers 

 in squares beside them give the mean values for viable hatch in 

 Series B. The cross marks the estimated position of maximum 

 viable hatch. 



FISHERY BULLETIN: VOL. 73, NO. 1 



significance of interaction by existing statistical 

 techniques. 



Acclimation of Spawning Fish 

 to Low Salinity 



On 20 October 1971 it was discovered that only 

 4 of the 26 fish acclimated to 15%o seawater were 

 females, whereas 15 of the 26 fish at 33%o were 

 females. The random assignment offish to the two 

 tanks had somehow resulted in a great disparity 

 in their sex ratios. Two of the four female fish from 

 15%o biopsied on 20 October 1971 had well- 

 developed ovaries, showing that gonadal matura- 

 tion can take place in a salinity of 15%o. The two 

 well-developed females, as well as one of the 

 poorly developed ones, were spawned with hor- 

 mone injections; the oocyte size-frequency dis- 

 tributions from biopsies of the three fish shortly 

 before injection are shown in Figure 14. 



Table 8. — Multiple regression equations for percentage fertilization, total hatch, and 

 viable hatch, as functions of temperature and salinity. Y = arcsin (percentage) '^,X = 

 temperature (C),X2 = salinity C/oo). 



order equations are useful in that they allow com- 

 putation of optimal conditions (Box 1956). The 

 resulting values (Table 9) show a thermal op- 

 timum at about 24°C for total and viable hatch in 

 both series, and optima of 23° and 25°C for fertili- 

 zation in Series A and Series B, respectively. The 

 calculated salinity optimum for fertilization was 

 considerably higher in Series B than in Series A 

 (36 vs. 31%o), but in both series the optimal 

 salinities for hatching were below those for fertili- 

 zation, ranging from 26 to 29%o. The optimal re- 

 sponses estimated at these points from the equa- 

 tions (Table 9) are below the maximal values ac- 

 tually recorded (cf Tables 2 and 7), another indi- 

 cation of the lack of fit of the second order polyno- 

 mial. The calculated positions of the optima, how- 

 ever, are the best available estimates of the true 

 optima. These experiments were designed primar- 

 ily to cover wide ranges of the two factors under 

 consideration, and the arrangement of treatments 

 unfortunately does not allow testing of the 



Table 9. — Optimum temperatures and salinities for fertiliza- 

 tion, total hatch, and viable hatch, estimated from the regression 

 equations (Table 8). Also listed are the optimum percentage 

 fertilization, total hatch, and viable hatch, calculated from the 

 regression equations at the estimated temperature and salinity 

 optima. 



The freezing point depression of blood serum 

 from fish acclimated to 15%o, determined by the 

 melting point method of Gross (1954), was 0.64 ± 

 0.066°C (mean± SD, n = 12 fish), and that offish 

 from 33«/oo was 0.63 ± 0.076°C (n = 12 fish). The 

 two groups did not differ significantly, nor was 



16 



