A SEROLOGICALLY DETECTED SERUM FACTOR ASSOCIATED WITH 

 MATURITY IN ENGLISH SOLE, PAROPHRYS VETULUS, AND PACIFIC 

 HALIBUT, HIPPOGLOSSUS STENOLEPIS ' 



By Fred M. Utter and George J. RIDGWAY^ Chemists 

 Bureau of Commercial Fisheries Biological Laboratory, Seattle, Washington 98102 



ABSTRACT 



An antigenic serum component in maturing female 

 pleuronectids was detected by immunodiffusion tech- 

 niques. Its presence was related to age, length, and 

 maturity in English sole {Parophrys vetulus) and Pacific 

 halibut (Hippo^lossus stenolepis). The factor had a 

 qualitative seasonal variation for English sole; the 

 highest incidence was during the spawning season and 

 the lowest at midsummer. The factor was detected in 

 all mature female halibut sampled, but complete sea- 



sonal data are lacking for this species because samples 

 were not available in summer and fall. The factor was 

 detected in the serum of some immature females of 

 both species during the spawning season. Evidence as- 

 sociating the synthesis of this factor with the produc- 

 tion of estrogenic hormones was obtained when estradiol 

 was injected into male English sole and induced them 

 to produce the factor. 



Maturity studies are an important aspect of bio- 

 logical investigations of fish. Knowledge of age 

 and size at maturity, fecundity, and duration and 

 frequency of spawning is generally required in the 

 management of a species. As a result of the impor- 

 tance of information on maturity, a wealth of litera- 

 ture exists on the subject covering a broad range of 

 fish species. Most maturity investigations have 

 been concerned with development of ovaries rather 

 than testes because of the importance of egg produc- 

 tion in population dynamics. 



Biological studies of maturity of the Pleuronec- 

 tidae (flounders) are representative of the variety 

 of approaches for fish generally. Pleuronectid ova- 

 ries may be easily classified as developing or imma- 

 ture by macroscopic inspection during the intervals 

 before and after (and including) the spawning season. 

 Harry (1959) used this method to study time of 



' This material was included in a thesis submitted by Mr. Utter in partial 

 fulfillment of the requirements for the M.S. degree from the Graduate 

 School of the University of WashinRton 



' Assistant Laboratory Director, Biological Laboratory, West Boothbay 

 Harbor, Maine. 



Not« — Approved for publication Sejitember 21, 1965. 



spawning, length at maturity, and fecundity in 

 three species of flounders. Use of a maturity scale, 

 devised by Heincke (1898) for North Sea herring 

 investigations, allows more quantitative estimates 

 of annual ovarian variations. To calculate the 

 spawning season of the Dover sole (Microstomus 

 pacijicus) Hagerman (1952) used a typical modifi- 

 cation of Heincke's scale, based on grossly discernible 

 criteria such as size, transparency, and presence of 

 macroscopic ova. More precise information can be 

 gained by examining the interior of the ovary. By 

 microscopic study of egg diameter and the develop- 

 ment of ova, Thompson (1915) determined the 

 presence of egg stocks for more than one season in 

 the Pacific halibut (Hippoglossus stenolepis) and 

 found an extended spawning interval for individual 

 females. Through histological methods, Franz 

 (1910) identified four distinct developmental stages 

 and established a firmer understanding of the ma- 

 turity process than could be done solely by e.xternal 

 observations of the ovary in plaice (Pletironedes 

 platessa). 



Characteristic changes in the blood of certain 



FISHERY bulletin: VOL. 60, NO. 1 



47 



