Radtke and Hourigan' Age and growth of Nototheniops nudifrons 



561 



Figure 4 



Relationship of sagittal otolith length to fish standard length (SL) 

 for Nototheniops nudifrons. 



Figure 5 



Relationship of sagittal otolith weight to fish standard length (SL) 

 for Nototheniops nudifrons. 



(Fig. 4), and sagitta weight was related exponentially 

 to fish length (SL) (Fig. 5). Ground, polished, and 

 decalcified sagittae were examined by SEM. A low 

 magnification view of a sagittal otolith (Fig. 6) shows 

 increments occurring concentrically from the center to 

 the edge. Larger incremental patterns, or bands, were 

 observed, but they could not be attributed to any 

 specific environmental cues. Counts of microincre- 

 ments within these bands showed that they were not 

 true annuli. Sagittae exhibited a well-defined central 

 core region or nucleus (Fig. 7a). Within the core region 

 were concentric microincrements separated from the 

 surrounding otolith by a distinct transition zone (Fig. 

 7b). Surrounding the core area were mineral crystals 

 in a protein matrix which formed microincrements (Fig. 

 8a and 8b). Counts of microincrements were made 

 beginning at the core transition zone and ending at the 

 outer edge of the otolith. These microincrements varied 

 in width from about 2 f^m (Fig. 8a) to less than 1 (.(m 

 (Fig. 8b). Differences in increment width may reflect 

 periods of differential growth. 



Validation of the daily nature 

 of microincrements 



The periodicity of growth increment formation was ex- 

 amined using tetracycline- and acetazolamide-marked 

 specimens which were held in tanks at ambient light 

 and temperature regimes after injection. After injec- 



tion of tetracycline or acetazolamide. A'', nudifrons 

 displayed some evidence of short-term stress, including 

 cessation of feeding for 2 or 3 days, but only one mor- 

 tality occurred. Subsequently, the fish survived well in 

 captivity, with 80% of all fish surviving the whole 

 winter. Sagittae of 29 fish injected with tetracycline 

 in February and March 1984 and held 4-34 days under 

 natural daylight photoperiods were examined for post- 

 treatment increments. A discrete fluorescent band was 

 discernible in all specimens, and increments between 

 the band and the margin of the otolith were counted 

 (Table 2). The number of increments averaged 2.5 in- 

 crements less than the number of days after injection. 

 This difference corresponded well to the initial period 

 of stress, and did not change with length of the experi- 

 ment (Median test, 0.2>p>0.1; Siegel 1956). Linear 

 regression analysis (Model I, Sokal and Rohlf 1969) in- 

 dicated that the slope (6 = 1.076, 95% CI of 0.756- 

 1.396) was not significantly different from 1 (Table 2). 

 The 2/-intercept equaled - 3.27 (95% CI of - 7.73-1.19). 

 Sagittae from five fish injected with acetazolamide 

 in April 1985 were examined by SEM. A discrete dis- 

 ruption of increments caused by the interruption of 

 calcium deposition was discernible (Fig. 9). The number 

 of increments from this disruption mark to the otolith 

 margin averaged 9.2 increments less than the number 

 of days after injection (Table 2). Acetazolamide disrupts 

 metabolic processes and its effects can be expected to 

 last longer than the tetracycline's, since the latter does 



