FERRARO: EMBRYONIC DEVELOPMENT OF ATLANTIC MENHADEN 



Brevoortia tyrannus embryo mortality w£is high 

 at the 10° C incubation temperature. In a prehmi- 

 nary laboratory experiment, naturally fertilized 

 B. tyrannus embryos at the blastodisc stage of 

 development (stage 2) from field plankton collec- 

 tions ( 14.7° C, 24%!)) failed to develop beyond stage 

 4 when the incubation temperature was lowered to 

 6°± 1° C. The lowest temperatures at which Atlan- 

 tic menhaden embryos have been collected in the 

 field generally range between 10° and 13° C 

 (Perlmutter 1939; Wheatland 1956; Richards 

 1959; Herman 1963), but they have been reported 

 in water as low as 7.7° C (Mundy^). The available 

 information, therefore, indicates that while 

 spawning rarely occurs in water <10° C, the low 

 lethal temperature of B. tyrannus embryos is 

 probably about 7° C. 



The temperature range in the experiments 

 (10°-25° C) was not sufficiently wide to determine 

 the upper temperature tolerance of S. tyrannus 

 embryos, which survived equally well at 15°, 20°, 

 and 25° C . There are no references in the literature 

 of Atlantic menhaden embryos in nature in water 

 >25° C. 



A number of investigators have noted that high 

 fish embryo mortalities tend to occur during gas- 

 trulation and just prior to or during hatching 

 (McMynn and Hoar 1953; Alderdice and Forrester 

 1971a; Laurence and Rogers 1976; and others). 

 High mortalities of B. tyrannus embryos occurred 

 only during gastrulation. 



Generally there is a linear or slightly cur- 

 vilinear relationship between the logarithm of the 

 development rate offish embryos and temperature 

 (see Blaxter 1969, fig. 4; Williams 1975; and 

 others). The embryonic development rate of B. 

 tyrannus followed this general rule (Figure 2). 



Brevoortia tyrannus embryo age-stage relations 

 at each of the four incubation temperatures were 

 nearly perfectly linear (Figure 1; Table 7). These 

 results imply a) the durations of the stages (Table 

 1) are approximately equal, b) the effect of the four 

 incubation temperatures on rate of development of 

 B. tyrannus embryos was relatively the same in all 

 stages, and c) the stages of development can be 



*Mundy,B.C. 1974. Order Clujwiformes Family Clupeidae 

 Brevoortia tyrannus (Latrobel, Atlantic menhaden. In H. M. 

 Austin (editor). Preoperational ecological monitoring program of 

 the marine environs at the Long Island Lighting Company 

 (LILCO) nuclear power generating facility, Shoreham, Long Is- 

 land, N.Y., vol. 2, sect. 5, p. 15-20. Contract SR-72-32. LILCO 

 Community Relations, 250 Old Country Road, Mineola, NY 

 11501. 



used to estimate the age of embryos if the incuba- 

 tion temperature is known and constant. 



A simple method of predicting the age of a B. 

 tyrannus embryo at any stage of development from 

 Table 1, incubated at any constamt temperature 

 (degrees Celsius) is to solve Equations (3) and (1), 

 in succession for B and age. At low temperatures 

 precision of the age estimate decreases because 

 duration of stages increases. At temperatures in 

 which menhaden commonly spawn (15°-20° C), 

 this method yields an estimate of embryo age with 

 an average expected error from stage duration of 

 between 1.3 and 2.3 h (average error = 'A x stage 

 development rate). 



Kuntz and Radcliffe (1917) and Hettler (1970) 

 gave the incubation time of fi. tyrannus embryos, 

 but Kuntz and Radcliffe did not specify the incuba- 

 tion temperature. Hettler (1970) observed hatch- 

 ing within 66-74 h at an average incubation tem- 

 perature of about 15.5° C (range 11.5°-19.5° C). 

 The embryo age calculated for stage 9 at 15.5° C 

 from the age prediction equations is 68.8 h, which 

 compares well with Hettler's observation. 



Other methods have been developed which es- 

 timate age of fish embryos. Simpson (1959) and 

 Brown and Hassler (1973) constructed nomo- 

 graphs recording the influence of temperature on 

 durations of embryonic stages of Pleuronectes 

 platessa and Morone saxatilis, respectively. 

 Ahlstrom (1943) and Talbot (1977) used regres- 

 sion analysis to describe the relationship between 

 temperature and durations offish egg stages, but 

 their methods require calculating separate re- 

 gressions for each development stage and temper- 

 ature and does not allow interpolation of develop- 

 ment rates between temperatures. Zweifel and 

 Lasker ( 1976) applied the Laird-Gompertz growth 

 equation to incubation times and embryonic 

 growth (extrapolated from early posthatch 

 growth) offish embryos. The Laird-Gompertz equa- 

 tion appears to give good predictions of fish em- 

 bryo growth, but its computation requires solving 

 a multiparameter equation by iteration for each 

 incubation temperature. The fish embryo age es- 

 timation method described in this paper is simple 

 and has broader practical applications than the 

 methods above. Together Equations (3) and (1) 

 accurately describe the age-stage-temperature re- 

 lations of B. tyrannus embryos at easily identi- 

 fiable stages, during the entire embryonic de- 

 velopment, and over a wide range of temperatures. 

 Embryo age prediction equations can be calcu- 

 lated for other species in the manner described 



947 



