40 



Fishery Bulletin 97(1), 1999 



sagittal otoliths were extracted for ageing purposes 

 and stored dry in coin envelopes. 



Fish age classes were determined by counting pre- 

 sumed annual growth increments in otolith sections. 

 For temperate-water fish, which generally exhibit 

 seasonal growth patterns, one year of growth is de- 

 fined by one opaque and one hyaline zone termed 

 the "annulus" (Pentilla et al., 1988). Sagittal otoliths 

 have been used for age determination in the major- 

 ity of commercially important gadids (Andrade and 

 Smith, 1988; Dery 1988; Pentilla, 1988) including £. 

 cimbrius (Cohen et al, 1990). The assumption that 

 increments were annual in E. cimbrius was based 

 on the following: prolonged spawning in the Gulf of 

 Maine (May-October) (Cohen et al, 1990), a pelagic 

 stage (40.0-45.0 mm TL) spanning several months 

 (Bigelow and Schroeder, 1953), time of year sample 

 was taken (August), and presence of a prominent 

 hyaline zone. The otolith of the smallest fish (95 mm 

 TL) in the present study exhibits a prominent hya- 

 line zone and this fish is assumed to have hatched in 

 the previous year. 



One otolith from each pair was embedded in a mix- 

 ture of 1 part carbon powder and 4 parts paraffin 

 wax, then sectioned dorsoventrally through the 



nucleus on an Isomet saw producing a section 203 

 |im thick. Sections were mounted on glass slides with 

 Crystal Bond 509, polished with 3.0-|i and 0.5-|i met- 

 allurgic lapping film, etched for 6 minutes with 5% 

 EDTA, and stained for 3 minutes with 0.1% tolui- 

 dine blue. Otolith sections were viewed under a com- 

 pound microscope at 40x by using transmitted light 

 (Fig. 1). Etching with EDTA provided three-dimen- 

 sional relief to the polished otolith surface, affording 

 the greatest resolution and definition of the hyaline 

 zones (Secor et al., 1992). 



To reduce sample size for age determinations, the 

 length-frequency distribution of £. cimbrius at sta- 

 tion 40 was used to generate a rarefaction curve. 

 Fifty-seven fish were aged by using both left and right 

 sagittal otoliths during one trial under the following 

 treatment effects: low-power dissecting microscope 

 (LD); high-power zoom stereomicroscope (HS); and 

 high-power zoom stereomicroscope after otoliths were 

 etched with EDTA and stained with toluidine blue 

 (EDTA). Nine fish were omitted from the analysis 

 because of the inability to obtain either the left or 

 the right otolith. 



Individual variances of the six trials were plotted 

 in groups of five to generate a rarefaction curve. The 



Figure 1 



Transverse section of a sagittal otolith etched with S'f EDTA and stained with O.Ol'/f toluidine blue photo- 

 graphed under a compound microscope at 40x by using transmitted light. 



