numbers; they are valuable for clarification of gen- 

 eral principles wliicli may be applied to other species 

 as well. 



SEPARATION OF MATURE FEMALES 

 FROM OTHER HM-POSITIVE INDIVIDUALS 



Separation of HM-positive males and immature 

 females from mature females appears possible by 

 quantitative means. The HM serum levels of ma- 

 ture female halibut taken during the spawning season 

 had titers above 200, whereas the titers of HM- 

 positive males and immature females, which were 

 found only at this time, were less than 2. 



An extension of the single diffusion ciuautitation, 

 as used in this study, may be applied where routine 

 ciuantitation is required. From figure 2 it can be 

 observed that the diameter of the precipitin ring 

 decreases regularly as the HM concentration de- 

 creases. A measurement of the diameter of the 

 precipitin ring formed by the undiluted fish serum 

 could give the approximate titer. 



AREAS FOR FURTHER INVESTIGATION 



Several areas for further study are evident. More 

 freiiuent and larger samples are desirable. As indi- 

 cated above, routine quantitation may l)e necessary 

 during the spawning season, and a knowledge of the 

 quantitative seasonal fluctuation of the HM factor 

 in a given species would be useful. Perhaps the 

 relative HM concentration can be related to such 

 factors as age, weight, or fecundity. More exten- 

 sive histological examinations of the ovary would 

 help, and a similar examination of the pituitary 

 gland may establish more fundamental criteria for 

 the occurrence of the factor. A biochemical assay 

 might indicate that the composition of the factor in 

 fishes is related to analogous components in other 

 vertebrates. 



THE BROADENING APPLICATION OF 

 SEROLOGY IN FISHERY RESEARCH 



Serological techniques have had increasing appli- 

 cation in fishery problems during recent years. This 

 research has been directed mainly toward racial 

 studies of serum antigens or red blood cell antigens. 

 Manj- of the current approaches to serological in- 

 vestigations of populations were discussed in a sym- 



posium moderated by Cushing (1902), and the sub- 

 ject has been reviewed recently by Marr and Sprague 

 (19t)3) and Cushing (H»(i4). 



Antigenic differences at species level have also 

 been investigated. Ridgway and Klontz (unpul)- 

 lishod data) and SindermaiHi (li)(i2) have found 

 distinct species-specific antigenic characteristics in 

 red blood cells and serum of species of Pacific salmon 

 and .Vtlantic cluijciods, lespectively. Ridgway (1903) 

 reported species-specific antigens in muscle tissue of 

 certain tuna species, in addition to species-s[)ecific 

 lilood serum components. This finding olTers a jios- 

 sible serological means of distinguishing larva^ of 

 these species. 



We hope that this study will help broaden the 

 interest in ai)plication of serological methods to 

 other areas of fishery biology. Recause components 

 similar to the HM factor have been detected in a 

 diverse range of teleosts, a similar approach presum- 

 ably could be used throughout this class of verte- 

 brates. We feel that this a|)proach can be a valuable 

 supplement to in\'estigating maturity in fish, though 

 perhaps not universally applicable. 



SUMMARY 



A serological investigation of a serum vitellin 

 factor in mature and maturing female flatfish was 

 made on English sole and Pacific halibut. Immuno- 

 diffusion techniques with antisera prepared in rab- 

 bits stimulated with egg vitellin extracted from 

 starry flounder eggs were u.sed to detect the factor. 

 In English sole the factor's occurrence was compared 

 with age, length, gonad weight, and gono-somatic 

 ratio. A qualitative sea.sonal variation was found; 

 individuals with heavier ovaries during the summer 

 were more likely to retain the factor in the scrum. 

 The presence of the factor in female halibut was 

 compared with length, age, and maturity. A ([uali- 

 tative seasonal variation in mature halibut could not 

 be studied because no samples were available tluring 

 the summer or autumn. The factor was found in 

 some immature females of both species during their 

 spawning seasons. Production of the factor in male 

 English sole by injections of estrogenic hormones 

 associates synthesis of the factor in females with 

 production of estrogen. Determination of the factor 

 appears to have potential value as a supplement to 

 other means of investigating maturity, particularly 

 in large species. 



56 



U.S. FISH AND WILDLIFE SKUVICE 



