Table 9. — Effect of estrone injections on the occurrence of 

 the HM factor in the serum of male English sole 



' Reriproral dilution. 



2 No control bleeding. 



The production of the HM factor in the serum of 

 male English sole after estrogenic stimulations and 

 the natural occurrence of the factor in male halibut 

 during the spawning season indicate that males 

 should be included in investigations of the HM 

 factor. The natural occurrence of the factor in 

 males may have a number of causes. Although the 

 testes of the HM-positive male halibut appeared 

 normal, the presence of the factor may have been 

 due to low-level secretions of estrogenic hormones. 

 Hermaphoditism has been reported in a diverse 

 range of tcleosts, including clupeids (Fowler, 1912), 

 salmonids (Ross, Yasutake, and White, 1963), silur- 

 oids (Singh and Sathyaneson, 1961), cyprinodonts 

 (Chidester, 1917), centrachids (James, 1946), and 

 scombroids (Uchida, 1961). A further possibility 

 is the stimulation by estrogenic hormones of exoge- 

 nous origin through ingestion of mature females of 

 smaller species of flatfish or possibly fish from other 

 families. Estrogenic hormones are effective when 

 administrated orally to mammals and presumably 

 could be similarly effective in fish. 



BIOLOGICAL IMPLICATIONS OF THE 

 PRESENCE OF THE HM FACTOR 



The English sole has been demonstrated to have a 

 qualitative seasonal ^■ariation of the HM factor. 

 The factor occurs first during the spawning season, 

 at least as early as the second year in some individ- 

 uals. After the spawning season through at least 

 midsummer, fewer and fewer individuals retain the 

 factor in the serum. As a new spawning season 

 approaches, the factor gradually reappears. 



Both the disappearance and the reappearance of 

 the factor are more pronounced with increase of 

 body length and ovarian mass. This relation may 

 be the result of resorption of residual vitellin 



retained with the ovary, since the large ovaries 

 retain a greater volume of unspawned ova. 



A ciualitati\-e seasonal variation was not found in 

 mature halibut, but we lack samples taken later 

 than June. Thompson (1915) reported a continuous 

 development of the ova which are to mature in the 

 succeeding generation in the spent halibut ovary; 

 vitellin synthesis may be a perennial process in the 

 mature female halibut. The detection of serum 

 vitellin in postspawning Atlantic salmon (Salmo 

 salar) by Fine and Drilhon (1964) suggests its peren- 

 nial occurrence in this species. 



The presence of the HM factor during spawning 

 season in immature females of both species indicates 

 that such an occurrence may be widespread among 

 the Pleuronectidae. Incomplete maturation pre- 

 ceding initial spawning in the Pleuronectidae has 

 been reported previously. Thompson (1915) stated 

 that contemporary investigators had found some 

 ova in immature pleuronectid females which ap- 

 peared ready to ripen but which failed to do so 

 because the ovary, as a whole, was not yet ready. 

 Franz (1910) reported finding this condition most 

 marked in plaice during the last winter preceding 

 initial spawning. 



PRACTICAL APPLICATIONS OF THE 

 HM FACTOR 



As a practi<'al procedure, the determination of 

 the HM factor appears to have its greatest potential 

 value in the larger pleuronectid species. In large 

 species such as halibut or starry flounder, the sex 

 cannot be determined at sight, except in ripe indi- 

 viduals. Small samples of blood taken at the time 

 of tagging could yield information on sex and matur- 

 ity without endangering the fish. Repeated bleed- 

 ings of four starry flounders kept in captivity did 

 not appear to endanger these fish. Routine prac- 

 tical applications to smaller species seem less likely. 

 The sexes of smaller flatfish species, such as English 

 sole, are generally evident by external examination; 

 and bleeding English sole, where required in this 

 study, caused high mortality. Evisceration of the 

 commercial halibut catch at sea does not preclude 

 practical application, since analysis of kidney- 

 fragment fluids can be made after the catch arrives 

 in port. On the other hand, smaller species are 

 brought to port in the round and sex information 

 can be obtained directly. Smaller species, however, 

 are frequently more readily available in greater 



SERUM FACTOR IN MATURITY 



55 



