3 o Memoir Sears Foundation for Marine Research 



Among the large species, accurate determination of the sex in specimens smaller than 

 30 inches is difficult and often requires the use of a magnifier. 



All of the species are oviparous and spawn in fresh water, and there is no adap- 

 tation for the care of eggs or young. The eggs are large, at least 2.5 mm in diameter, 

 demersal and adhesive (prior to water-hardening), and their number varies with the 

 species and with the size of fish; in large specimens they exceed several million, as 

 in the case of the 2,707-pound female reported by Berg (above), which yielded an 

 estimated 7.7 million eggs weighing 542 pounds. More details are given in the ac- 

 counts of the respective species. 



In all Acipenseridae*^ the ripening gonads^* have a characteristic appearance, 

 being thick and elongate and extending along each side of the air bladder near the 

 dorsal surface of the body cavity. The immature gonads in both sexes are covered on 

 the underside by a large mass of yellow fat which apparently plays a role of energy 

 storage for the ripening gonads; in those close to spawning it is almost entirely absorbed. 

 The fully mature ovaries are very large and make up io-20°/o of the total weight of 

 the fish. As the ripe eggs become dark,^^ the whole ovary darkens. Mature testes 

 are pale yellow to whitish. 



It is a common observation that, even in the spring during the spawning season, 

 large individuals with immature ovaries are found among fully mature females. This 

 may be explained by the fact that the fish, after the first spawning, may spawn only 

 at intervals of two or even three years. 



Studies of gonad maturation in A. nudiventris from the Aral Sea found that 

 there are two distinct "waves" in the ripening process (75: 581-584). Fish ascend 

 the Syr Darya River for spawning around the end of July, when they have rather 

 well developed gonads. Soon the advanced sex cells are absorbed. After about two 

 weeks, during the second "wave," the maturation of gonads starts again and is nearly 

 complete by mid-October. During the winter the maturing fish hibernate in the river 

 and spawn the following April or May. However, the material at Trusov's disposal 

 was rather limited (160 gonads) and was collected during four dififerent years (1941, 

 1946-1948). 



Habits and Food. Sturgeons are sluggish but strong. During the summer they often 

 leap from four to six feet above the water. There are many known cases of Sturgeons 

 jumping into a passing boat. About 70 years ago Ryder mentioned such a case for 

 A. oxyrhynchus near Delaware City, and on August 14, 1951, the Quebec newspaper 

 Le Soleil (p. 20) reported that a 35-pound A.fulvescens jumped into a small rowboat 

 on the Ottawa River, near Pembroke, Ontario. 



The small protractile mouth preceded by four sensitive barbels in the middle of 

 the lower surface of the head may be considered an adaptation for bottom feeding. 



13. The same phenomenon has been reported for Polyodon as well {46: 1 16-124). 



14. For further details on the ripening of eastern American Sturgeons, see Ryder (65: 268-273). 



15. Nikitin [56: 76) gives practical suggestions for the recognition of eggs from different species of Sturgeon made 

 into caviar. The eggs may be distinguished by size, color, and particularly by the tint of their germinal disc 

 ("eye" of the egg). 



