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Fishery Bulletin 90(2). 1992 



classification as a basis for the comparison of oocyte 

 and embryonic development between populations, 

 reproductive years, and other species of Sebastes. Such 

 data may be used to monitor reproductive development 

 during a particular year. In addition, descriptions of 

 oocyte and embryonic development provide a basis to 

 compare the impacts of environmental fluctuations and 

 physiological responses with the production of viable 

 offspring. An understanding of environmental and 

 physiological interactions influencing reproductive suc- 

 cess could provide valuable contributions to the under- 

 standing of recruitment dynamics and allow for more 

 efficient resource management. 



Materials and methods 



Specimens were collected from Cordell Bank (38°00'N, 

 123°25'W), a seamount 20 miles west of Pt. Reyes, at 

 monthly intervals. Adult female yellowtail rockfish 

 were captured by hook-and-line at depths of 50-150 m, 

 from May 1985 through April 1986. No samples were 

 obtained in June 1985 due to inclement weather. Mean 

 age and size of samples for each month are shown in 

 Table 1. 



Fish were held on ice and transported to the labora- 

 tory where pieces of ovaries ("^^4 x 4 x 6 mm) were dis- 

 sected and fixed in 10% neutral buffered formalin. 

 Routine paraffin embedding followed the guidelines of 

 Humason (1967). Samples were sectioned at 6^ thick- 

 ness with a rotary microtome. Mounted sections were 

 stained in hematoxylin and counterstained in eosin 

 (H&E). 



Cell measurements were made using a video coor- 

 dinate digitizer (Model 582 AVCD, H.E. Inc., Las 

 Vegas, NV) on cells sectioned through the nucleus. 

 Oocytes were measured and staged randomly. Mean 

 cell diameters were determined from a subsample of 

 10-20 cells for each stage. All cell diameters reported 

 are from fixed tissues. 



In each monthly sample, the first 200-400 cells en- 

 countered were counted and staged. Percent frequen- 

 cy distributions of the various oocyte stages were 

 calculated by dividing the total number of a particular 

 stage by the total number of oocytes observed, ex- 

 pressed as a percentage. Because the probability of an 

 individual oocyte being sectioned is proportional to its 

 size as well as its abundance, larger oocytes tend to 

 be overestimated and smaller oocytes underestimated 

 (Howell 1983). Nonetheless, frequency distributions do 

 indicate seasonal changes within the ovary. Because 

 of the wide range of cell diameters, overlapping sizes 

 among oocyte stages, and shrinkage due to fixation, 

 criteria for staging oocytes was based on histological 

 appearances and cell structure. 



Although ovaries in varying stages of postfertiliza- 

 tion development were observed, monthly collection of 

 ovaries was inadequate for a detailed study of rapid 

 embryonic development. Therefore, additional samples 

 of embryonic stages were collected by catheterization 

 from female yellowtail rockfish held in captivity. Ten 

 adult female yellowtail rockfish captured after copula- 

 tion were catheterized weekly for 6 weeks while being 

 maintained in a flow-through, sand-filtered (to 10f.<) sea- 

 water system. Photoperiod was ambient. The mean 

 temperature and salinity (10.4°C and 34.7"/oo) for the 

 2-month holding period (January and February) were 

 well within the range of parameters at the sampling 

 site. 



