HETTLER: DESCRIPTION OF Ol'LF MENHADEN 



DESCRIPTION 



Embryos 



Gulf menhaden eggs were spherical, and had an 

 unsculptured chorion, a faintly segmented yolk, and a 

 single oil droplet. Living eggs were buoyant in 

 salinities >26%o. Twenty-seven percent had both an 

 outer and inner chorionic membrane. This has not 

 been reported in wild-caught Brevoortia eggs. This 

 inner chorion was not an artifact of preservation, 

 since live eggs also contained a double chorion, but 

 may have been a result of induced ovulation by HCG 

 and carp pituitary. Dimensions of preserved and live 

 eggs were the same as maximum sizes given by 

 Houde and Fore (1973) for gulf menhaden eggs taken 

 in plankton collections (Table 1). At its widest point 

 the perivitelline space was 24-28% of the egg 

 diameter. Eggs produced during December 1982 by 

 another spawning group of gulf menhaden were 

 smaller than gulf menhaden eggs produced the year 



TABLEl. Mean diameter (mm) of j-cull menhaden, Hrevnnrtia pa- 

 tronus, eggs. Numbers in parentheses are equal to one standard 

 de\ iation oi the mean. 



Eggs 



Total 

 diameter 



Inner chorion 



diameter (if 



present) 



Yolk 



diameter 



(along axis) 



Oil droplet 

 diameter 



Preserved 100 1.29(0.04) 

 Live 100 1.30(0.05) 



1.23 (0.04) 

 1.25 (0.03) 



0.95 10.05) 

 97 (0.04) 



0.20(0.02) 

 0.19 (0.01) 



before; total diameter was 1.18-1.22 mm; the yolk 

 diameter was 0.66-0.79 mm; the oil droplet was 0.16 

 mm. The adults producing these eggs were smaller 

 (17.8 cm mean length, 90 g mean weight) than the 

 spawners that produced the larger eggs (20 cm, 135 

 g) (Table 1). Small adult size may be responsible for 

 the small eggs as well as the reduced fecundity. Only 

 a few hundred fertilized eggs were collected from the 

 December 1982 group of 20 fish. 



Advanced embryos had 30-40 small melanophores 

 on each side along the dorsal surface from the pos- 

 terior end of the head to the notochord tip (Fig. 1 A). 



1 mm 



V^frA 



FIGURE 1.— Early stages oiBrevoortia patronus. A. Embryo 40 h after fertilization. B. 2.6 mm larva, 5 min after hatching, e. 3.5 mm larva, 1 d 



after hatching. D. 3.9 mm larva, 2 d after hatching. 



87 



