FISHERY BULLETIN: VOL. 77, NO. 4 



Age =B (S - 1). 



(1) 



The results (Table 7; Figure 1) showed that agt 

 stage relations were nearly perfectly linear as a 

 function of incubation temperature, and the re- 

 gressions were highly significant (Table 7). 

 Analysis of variance of the regression coefficients 

 showed that development rates were highly sig- 

 nificantly different among temperatures iFiS, 57) 

 = 1,405.0;P<0.001). (Regression coefficients (fi's) 

 of Table 7 represent the "stage" development rate 

 (units: hours/stage) of embryogensis in B. tyran- 

 nus and are only meaningful when used in context 

 with the embryo staging classification in Table 1 . ) 

 The linear relationship between the logrithm of 

 the stage development rate ofB. tyrannus (B ) and 

 temperature (7' in degrees Celsius) (Figure 2) is 

 expressed by the following: 



logio 



B 



1.923 - 0.059 T. 



(2) 



The temperature coefficient (Qi^) forB. tyran- 

 nus embryonic development from fertilization to 

 hatching at 10° to 25° C determined by Equation 



Table 7. — Linear regression o{ Brevoortia tyrannus embryo age 

 (A) in hours since fertilization on morphological stage of de- 

 velopment (S). 



 = P<0.001. 



2.0-1 



Log B= 1.923-.059 T 



CD 



o 



1.5- 



1.0- 



0.5- 



5 10 15 



TEMPERATURE 



20 



C ) 



Figure 2. — Linear regression of the log^^^ of the "stage" de- 

 velopment rate ofBrevoortia tyrannus embryos (B) on tempera- 

 ture (T). Coefficient of determination = 0.96; SE regression 

 coefficient = 0.0084. 



(2) is 3.89. The relation between the logarithm of 

 the embryonic development rate of fish and tem- 

 perature, though, is not necessarily linear (Kinne 

 and Kinne 1962; Fonds et al. 1974), and, therefore, 

 best predictions of stage development rates of B. 

 tyrannus embryos (fi) incubated at constant tem- 

 perature (T in degrees Celsius) are obtained from 

 the explicit empirical equation: 



logj„ fi = -0.193 + 17.193 7^ 



+ 34.090 r' - 461.276 T 



(3) 



DISCUSSION 



The B. tyrannus embryo rearing experiments 

 were mainly designed to determine effects of tem- 

 perature and salinity on development rate; how- 

 ever, the results also have a bearing on tempera- 

 ture and salinity effects on embryonic survival. 



Wide salinity tolerances have been reported for 

 many marine fish embryos (Holliday 1969). Bre- 

 voortia tyrannus embryos have a salinity toler- 

 ance range >10-30%o, and they are, therefore, 

 euryhaline by Kinne's (1964) criteria. Atlantic 

 menhaden embryos have been collected in water 

 with salinity as low as 18.15%" (Wheatland 1956), 

 but according to Reintjes (1967) most spawning 

 occurs ". . . in the ocean or in inshore waters with 

 salinities similar to those of the ocean." It would 

 appear, therefore, that B. tyrannus embryos can 

 tolerate low salinity conditions not normally en- 

 countered in nature. 



Details of the salinity-development rate rela- 

 tion are species dependent, and they may be com- 

 plicated by the influence of salinity on dissolved 

 oxygen (Kinne and Kinne 1962; Forrester and Al- 

 derdice 1966), and the hatching process (Kinne 

 and Kinne 1962; Alderdice and Velsen 1971); but, 

 within limits, salinity effects on embryonic de- 

 velopment rates tend to be small or insignificant 

 for most marine fishes studied (e.g., McMynn and 

 Hoar 1953; Alderdice and Forrester 1968, 1971a, 

 b). Slight but apparently significant positive 

 relations between embryonic development rate 

 and salinity have been reported in some oceanic 

 species (Forrester and Alderdice 1966; Laurence 

 and Rogers 1976). Embryos of oceanic species are 

 probably more sensitive to low salinity and 

 changes in salinity than estuarine species. In the 

 experiments presented in this paper, salinity be- 

 tween 10 and 30"/cio had no noticeable effect on the 

 embryonic development rate of B. tyrannus. 



946 



