HOSIE and HORTON: BIOLOGY OF REX SOLE 



each fish and stored in 10% Formalin. 7 Estimates 

 of fecundity were obtained gravimetrically, 

 following the method described by Harry (1959). 



To obtain fish for tagging, short tows of about 15 

 min were made in March and June 1970 off 

 northern Oregon near the mouth of the Columbia 

 River. Any rex sole caught were held for 15-60 min 

 in a tank containing running seawater. Fish in 

 good condition were tagged and released. Petersen 

 disc (vinyl) tags, 16 mm in diameter, were at- 

 tached by a stainless steel pin inserted through 

 the musculature about Vz inch below the midbase 

 of the dorsal fin. Fishermen were advised of the 

 tagging program, and a $0.75 reward was offered 

 by the FCO for each tagged rex sole returned. 



Electrophoresis was used to investigate stock 

 identification of rex sole. A preliminary electro- 

 phoretic examination was conducted using muscle 

 tissue of 145 rex sole collected in April 1973 in 

 three nearly equal samples taken off northern, 

 central, and southern Oregon. Tissue extraction 

 and starch gel electrophoresis procedures followed 

 the methods of Johnson et al. (1972). Tests were 

 conducted for polymorphisms in muscle protein 

 and the five enzyme systems: aspartate 

 aminotransferase (AAT) A-I and A-II; lactic 

 dehydrogenase (LDH); peptidase A-I and A-II; 

 phosphoglucomutase (PGM); and tetrazolium 

 oxidase (TO). 



RESULTS AND DISCUSSION 



Length-Weight Relationships 



Length and weight were closely correlated, with 



7 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



the derived coefficient of determination (r 2 ) vary- 

 ing from 0.9902 to 0.9988 for males and from 

 0.9872 to 0.9966 for females (Table 2). These 

 coefficients of determination varied little by 

 season, possibly because of the extended spawning 

 period (Villadolid 1927) in the first half of the year. 

 Based on data in Table 2, we calculated mean 

 weights by season at representative lengths. For 

 both sexes weight increase was greatest in the 

 third quarter, average in the second quarter, and 

 slowest in the first and fourth quarters (Table 3). 

 Among mature fish, about 30 cm TL and larger, 

 females generally were slightly heavier than 

 males of the same length (Figure 1). A total of 950 

 males and 1,121 females were included in the 

 length-weight data analyzed. 



Age and Growth 



Validity of the Aging Technique 



Opaque or hyaline zones occur on the margin of 

 rex sole otoliths. These zones mark the respective 

 periods of rapid or slow growth. Examination of 

 265 otoliths from rex sole <27 cm TL collected off 

 northern Oregon from September 1969 through 

 July 1970 revealed that hyaline edges were first 

 observed in September (Figure 2). No hyaline 

 edges were present the previous June or July. In 

 the fall the percentage of otoliths with a hyaline 

 zone on their edge began to increase. By January 

 the majority of otoliths had a hyaline zone on their 

 edge. The percentage rapidly increased and 

 peaked in March when 92.3% had hyaline zone 

 margins. Conversely, opaque zones on edges were 

 at their lowest in March, gradually increasing 

 until June or July when all otoliths had opaque 

 edges. 



TABLE 2. — Length-weight relationship (log 10 W = log 10 a + b logL) by quarterly period for male and 

 female rex sole collected off central and northern Oregon, 1969-72. ' 



'Regression analysis conducted on 1 1- to 36-cm males and 1 1- to 51 -cm females. 



53 



