190 



Fishery Bulletin 92(1), 1994 



Figure 1 



Location of trawling grounds in the study area, Hecate Strait, British 

 Columbia, Canada. 



to the nearest 5 p, or with a projection microscope 

 calibrated to the nearest 4 u. Three hundred oocytes 

 were measured from at least one fish for every cm 

 length interval for each sample (Table 1). Measure- 

 ment of 300 oocytes per fish was necessary to pro- 

 vide complete information on the size composition 

 of developing oocytes. Only oocytes that had been 

 sectioned through the nucleus, close to the center of 

 the oocyte, were measured. Mean diameter was es- 

 timated as the mean of the minimum and maximum 

 diameters for each oocyte (Foucher and Beamish, 

 1980). For smaller oocytes (10-20 p), precision of the 

 measurement was lower because of distortion of the 

 oocyte by surrounding maturing oocytes (Dunn, 

 1970). A description of the histological stage of oo- 



cyte development (Fargo and Sex- 

 ton, 1991 4 ) was also recorded. 



We were unable to obtain oocyte 

 measurements from ovaries col- 

 lected from ripe fish in October 

 and November 1990. These 

 samples were taken from com- 

 mercial vessels at ports of land- 

 ing. Ovaries from these samples 

 had combinations of hydrated and 

 non-hydrated oocytes with many 

 burst cells. These fish had been 

 held in chilled seawater for sev- 

 eral days prior to sampling, prob- 

 ably exacerbating the state of hy- 

 drated oocytes and causing them 

 to burst. Since oocyte diameter 

 data for these samples would 

 have been biased (because most 

 measurable oocytes would not 

 have reached the hydrated state) 

 the slides from these samples 

 were used only to assess the his- 

 tological stage of the oocytes. This 

 problem did not occur with the 

 November 1987 sample collected 

 at sea on a research vessel. 



Prior to statistical testing of the 

 data, we tested oocyte size distri- 

 butions for normality using the 

 Shapiro-Wilk test. We applied two 

 sample £-tests to test for differ- 

 ences in the mean diameter of 

 previtellogenic and vitellogenic 

 oocytes between months within 

 years and among years. We used 

 linear regression to investigate 

 the relation 1) between fish 

 length and mean oocyte diameter 

 within months and 2) between 



fish length and mean oocyte diameter at the time of 



spawning. 



Results 



Oocyte development 



Ovaries were examined from 174 fish (Table 1) 

 caught at five locations in Hecate Strait (Fig. 1). The 

 sampling period encompassed seven different 

 months over three years. Descriptions and micro- 



4 Fargo, J., and T. Sexton. 1991. A quide to the ovarian histol- 

 ogy of English sole iParophrys vetulus). Can. MS. Rep. Fish. 

 Aquat. Sci. 2133, 19 p. 



