Sparks, A. K., J. Hibbits, and J. C. Fegley. 



1982. Observations on the histopathology of a systemic ciliate 

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 Summers, F. M., and G. W. Kidder. 



1936. Tkxonomic and cytological studies on the ciliates asso- 

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 Arch. Protistenkd. 86:379-403. 



Phyllis T. Johnson 



Northeast Fisheries Center Oxford Laboratory 

 National Marine Fisheries Service, NOAA 

 Oxford, MD 21654 



FECUNDITY OF THE PACIFIC HAKE, 



MERLUCCIUS PRODUCTUS, 

 SPAWNING IN CANADIAN WATERS 



Previous studies on the fecundity of Pacific hake, 

 Merluccius productus, have been concentrated on the 

 coastal stock in Baja California (MacGregor 1966, 

 1971; Ermakov et al. 1974), although large-scale 

 spawning events have been recorded as far north as 

 lat. 38°N, near San Francisco, CA (Stepanenko 

 1980). The present work was undertaken in conjunc- 

 tion with ichthyoplankton surveys, aimed at esti- 

 mating the released egg production and spawning 

 biomass of the Pacific hake stock resident in the 

 Strait of Georgia, a semi-closed marine basin in 

 British Columbia (Thomson 1981). The spawning 

 season extends from February through June, peaks 

 in early April, and is 90% complete by mid-May 

 (Mason et al. 1984). 



In comparison with the coastal stock of some 1-2 

 million metric tons (t) (Bailey et al. 1982), this in- 

 shore stock, of about 140,000 t, is subject to modest 

 annual exploitation (1-500 t) and resides in a semi- 

 estuarine environment on the known northernmost 

 edge of the reproductive range. The coastal stock 

 undertakes a northward feeding migration after the 

 spring spawning and reaches the southwest coast of 

 Vancouver Island by late summer (Bailey et al. 1982). 

 There is no evidence of intermingling between these 

 two stocks, based on their distributional patterns. 

 The inshore stocks in the Strait of Georgia and Puget 

 Sound may undergo some exchange, possibly due to 

 surface transport of larvae produced in the central 

 Strait of Georgia (Mason et al. 1984). The Puget 

 Sound and coastal stocks have been identified as 

 genetically distinct by Utter and Hodgins (1971), 

 but the two inshore stocks in Puget Sound and 



the Strait of Georgia have not been similarly com- 

 pared. 



Histological analysis has indicated that only one 

 mode of oocytes developes in Georgia Strait hake. 

 However, like the Baja, California form and hake 

 species elsewhere, some Strait of Georgia hake show 

 evidence of ovarian resorption following spawning 

 (Foucher and Beamish 1980). The quantitative sig- 

 nificance of resorption relative to individual and 

 stock fecundities, or to their potential physiological 

 and environmental correlates have not yet been ex- 

 amined. This report considers the "apparent fecun- 

 dity" as an annual expression of reproductive poten- 

 tial applicable to the stock in the Strait of Georgia, 

 determines that fecundity, and concludes that 

 ovarian resorption is of minor consequence in the 

 stock. 



Materials and Methods 



The ovaries of 97 Pacific hake females 39-82 cm 

 FL were collected during late February and early 

 March of 1980 and 1981, 71 of which were collected 

 in 1981 (McFarlane et al. 1983). Unspawned females 

 were selected in maturity stages R 2 and R (Foucher 

 and Beamish 1977) when the ovary is yellow and 

 opaque, has prominent blood vessels, and fills one- 

 third to one-half of the coelomic cavity. No ovaries 

 contained translucent oocytes which signify immi- 

 nent spawning. Fresh ovaries were preserved in 10% 

 formaldehyde solution. In the laboratory, the pre- 

 served ovaries were transferred to modified (Simp- 

 son 1951) Gilson's fluid for several months to allow 

 breakdown of connective tissue 



Ovaries were then washed thoroughly in cold water 

 over a series of stainless steel screens of 40 jum and 

 larger aperture, and gently broken up by hand when 

 necessary to separate the hardened eggs from the 

 ovarian tissue The mesh size of the finest screen was 

 determined by the difficulty encountered in separ- 

 ating oocytes <40 ^m diameter from ovarian tissue 

 The cleaned eggs were then stored in 5% formal- 

 dehyde solution in preparation for analysis. 



Eggs from a single ovary were transferred to a 

 20 L glass reservoir filled to either 10 or 15 L. While 

 the reservoir was being stirred vigorously with a 

 wooden paddle in a rotating figure-eight pattern, a 

 second worker extracted 50 1-2 mL volumetric sub- 

 samples using Stempel pipettes and transferred 

 them to petri dishes. Under the dissecting micro- 

 scope at 50 x magnification, all eggs in five subsam- 

 ples were sized and counted in 20 /urn intervals of 

 oocyte diameter. These results were then combined 

 to construct oocyte size-frequency histograms and 



FISHERY BULLETIN: VOL. 84, NO. 1, 1986. 



209 



