WATANABE ET AL.: GROWTH OF SAURY 



Sagittae were dissected out from fish and left to 

 dry after removing tissues and membranes. We used 

 a dissecting microscope with a polarizing filter to 

 dissect otoliths from small larvae and juveniles. The 

 otoliths were read either by light microscopy (LM) 

 or by scanning electron microscopy (SEM). Otoliths 

 that were to be read by LM were mounted in 

 EUKITT^ after dissection. Otolith radius was 

 measured from the focus to posterior margin and 

 the increments were counted along the same tran- 

 sect using the otolith reading system, which was 

 developed by the Southwest Fisheries Center of 

 the National Marine Fisheries Service, NOAA, and 

 which consists of a light microscope, a video 

 monitor, a micro-computer, and a digitizer (Methot 

 1981). 



For SEM, otoliths were mounted in epoxy or 

 methacrylate resin. The otolith radius was measured 

 from the focus to the posterior margin with an 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



optical comparator. The otoliths were ground 

 oblique to the sagittal plane parallel to the long 

 axis of the otolith in order to have a flat plane 

 through the otolith nucleus. The polished surface 

 was washed in xylene, using an ultrasonic washer, 

 then dried and etched for 50 seconds with 0.2M 

 EDTA-2Na (disodium ethylenediaminetetraacetic 

 acid). The etched surface was coated with palladium 

 platinum and observed under an SEM (JSM-25) at 

 15 kV. 



The three authors of this paper read saury oto- 

 liths independently: the senior author read fish from 

 the western Pacific up to 85 mm by LM, the second 

 author read otoliths from the eastern Pacific by LM, 

 and the third read otoliths from the western Pacific 

 larger than 38 mm by SEM. To confirm that we 

 were all interpreting the same structure as growth 

 rings by SEM and LM, we compared 50 data points 

 read by SEM and 14 points read by LM for west- 

 ern Pacific sauries between 38 and 85 mm. The 

 distribution of increment number versus knob length 

 was the same. We also checked for possible biases 

 for the two readers using LM by having each read 

 the same set of otoliths independently. 



130°W 120°W 



dots indicate sample numbers in Table 1. 



RESULTS 



The nucleus of a Pacific saury sagitta is approx- 

 imately 20 ^m in diameter and is composed of four 

 to six small dense bodies which appear to be assem- 

 blages of calcareous spherules (Fig. 2a). These dense 

 bodies are separated from one another and each is 

 surrounded by a small concentric ring. 



We observed the nucleus areas of otoliths from 

 Pacific sauries collected in the western Pacific in 

 1985 (sample # 15-22) and found that most of 

 them had a distinct ring of about 27 fim in radius. 

 Between the nucleus and this distinct ring, four 

 (or five) indistinct growth rings were detected (Fig. 

 2b). 



We measured knob lengths of 27 larval and juven- 

 ile Pacific sauries before freezing and after thaw- 

 ing, and found that the ratio of these two measure- 

 ments was 0.997. There was virtually no shrinkage 

 by freezing and thawing. Theilacker (1980) found 

 that preservation of larval northern anchovy, 

 Engraulis mordax, in 80% alcohol did not cause 

 additional shrinkage of the body after net treatment. 

 Thus, knob lengths after both 80% alcohol preser- 

 vation and freezing are comparable to each other, 

 and this measurement corresponds to the size after 

 net treatment. Since shrinkage factors by net treat- 

 ment are not known for the saury, lengths are un- 

 corrected for net shrinkage. 



491 



