BOLZ and LOUGH: GROWTH OF LARVAL COD AND HADDOCK 



2 sagittae, 2 lapilli, and, when possible, 2 asterisci 

 were dissected from the larvae and mounted whole 

 on microscope slides with Permount 5 . The growth 

 increments on most of the otoliths were discernible 

 without any further preparation. 



The largest of the otolith pairs, the sagittae, were 

 then viewed under a Zeiss compound microscope 

 with transmitted light. The number of growth 

 increments were counted from the image projected 

 by a drawing tube onto a Zeiss MOP Digital Image 

 Analyzer System. This method was found to be 

 superior to the microscope-television system used in 

 previous studies (Lough et al. 1982) in terms of both 

 increment resolution and the time necessary for 

 repetitive counts. Depending on the size of the 

 otolith, magnifications used ranged from 400X to 

 1,000X. Three counts were made on one of the 2 

 sagittae from each larvae, and those otoliths with a 

 repeatable increment count of >95% were used in 

 the growth analysis. The other sagitta was counted 

 once for comparison. 



The following measurements were made routinely 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



on each sagitta to the nearest micron (Fig. 2): 1) 

 Anterior and posterior radii from the center of the 

 otolith nucleus to the outer edge of the otolith (otolith 

 length); 2) diameter of the sagitta perpendicular to 

 the length (lateral diameter); 3) diameter of the 

 nucleus; 4) diameter of that portion of the otolith 

 deposited prior to yolk-sac absorption as defined by 

 Radtke and Waiwood (1980); and 5) planar surface 

 area of the entire otolith. Diameters and planar sur- 

 face areas of the lapilli and asterisci also were 

 measured. 



In order to distinguish faint increments within and 

 immediately outside of the nuclear check, several 

 otoliths of both cod and haddock larvae were 

 examined by using a scanning electron microscope 

 (SEM). After securing the otoliths to a microscope 

 slide with Clear 2-Ton epoxy, they were ground with 

 1 ju.m diamond polishing compound. The grinding 

 procedure was monitored periodically by viewing the 

 otolith under a compound microscope. Next, the 

 otoliths were etched with 10% HC1 for 5-15 s. The 

 epoxy containing the ground and etched otolith was 

 removed from the slide, attached with double- sided 

 tape to SEM viewing stubs, and sputter- coated with 

 gold-palladium using a Tousimis Samsputter-2A. 



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FIGURE 2.— Larval Atlantic cod and haddock otoliths. 

 Bar of photographs represents 20 /xm. a = anterior, p = 

 posterior, nc = nuclear check, yc = yolk-sac check. A. 

 Sagitta from 31-d-old cod larva, 12.2 mm SL (400X). B. 

 Sagitta from 47-d-old cod larva, 13.3 mm SL (630X). Note 

 poorly defined region enclosed by yolk-sac check followed 

 by increments of increasing thickness towards the edge of 

 the otolith. C. Sagitta and lapillus from 31-d-old haddock 

 larva, 10.7 mmSL(160X). 



829 



