BIOLOGY AND NATURAL HISTORY 99 



The most extensive and complete investigation on the spawning of men- 

 haden has been done in Long Island waters by Perlmutter. 



He places the spawning time from May to October with the height in May. 

 The season is prolonged and spawning apparently very prolific, Perlmutter 

 found that the eggs of the menhaden represented a large proportion of the 

 total egg catch of all species collected in 1938. Perlmutter established a wide 

 latitude in both temperature and salinity conditions. He found spawning 

 freely taking place between 55° and 80° F., and a salinity from 84 to 100 

 per cent sea water. Since the incubation period is short (Bigelow and Welsh, 

 1925), there must be a high tolerance to temperature and salinities or a 

 great mortality must result. Since Perlmutter found both larvae and eggs 

 under the reported conditions, it may be concluded that the tolerance is high. 



According to Bigelow and Welsh (1925) sexual maturity is attained in 

 the season following the third winter. The sexes are not distinguishable by 

 external characteristics (Hildebrand and Schroeder, 1928). In one specimen 

 reported (Goode, 1884), 150,000 eggs were found. Hardcastle (unpublished 

 manuscript) has found over 41 per cent of the mature and immature males 

 to be infested with a gonadal parasite, Eimeria brevoortia. In some cases 100 

 per cent of the mature males have the parasite. Hardcastle does not indicate 

 whether or not sterility results. 



EMBRYOLOGY. The eggs are buoyant, highly transparent and 1.4 to 1.6 mm. 

 in diameter. The perivitelline space is very large, resembling the shad and 

 European pilchard eggs. The yolk sphere is approximately 0.9 mm. in diam- 

 eter and contains a transparent oil globule 0.12 to 0.14 mm. in diameter. The 

 egg membrane is thin and horny (Kuntz and Radcliffe, 191 7). 



Welsh found by experiment that the incubation period does not exceed 48 

 hours (Bigelow and Welsh, 1925). The newly hatched larvae are approxi- 

 mately 4.5 mm. long and slender with yolk sac attached. The pigmentation 

 is less than before hatching, and small black chromatophores appear on 

 dorsal aspect of the body and on ventral aspect posterior to vent. 



Four days after hatching, the larva is 5.7 mm. in length. In the 9 mm. fish 

 the dorsal and ventral fins begin to differentiate and the posterior gut has 

 become distinctly convoluted. At 23 mm. all fins are well differentiated, but 

 the body is still slender, and at 33 mm. scales appear. The fish remains 

 slender. At 41 mm. most of the characteristics of the adult have appeared. 

 The body proportion has been acquired and the shoulder blotch is distinct 

 (Kuntz and Radcliffe, 191 7; Bigelow and Welsh, 1925). 



In the young larval and fry stages the menhaden are very similar to the 

 herring and almost indistinguishable, but according to Bigelow and Welsh 

 (1925), the differentiation of appendages and similarity to the adult occurs 

 at a much smaller stage in the menhaden, a menhaden of 20 mm. length in 

 this respect being far more advanced than a herring at 35 mm. 



