304 
Fishery Bulletin 11 6(3-4) 
Data analysis 
The number of increments deposited in larval oto¬ 
liths in each of the 2 aquaria (i.e., the replications) 
after 7, 14, 22, and 28 days were compared by us¬ 
ing Atests conducted separately for each of the 4 
age groups. Age validation was completed by fitting 
linear regression to increment number-at-age data 
and by analyzing the slope for the difference from 
1 (analysis of covariance [ANCOVA]). Otolith size- 
at-age and otolith size-at-SL data were described 
with best-fit functions to better visualize the pat¬ 
terns observed. Best-fit models for the relationship 
of fish growth to size (in SL) and weight at age are 
also presented. Statistica, vers. 12.0 (TIBCO Soft¬ 
ware, Inc., Palo Alto, CA) software was used for data 
analysis. Differences were considered statistically 
significant at P<0.05 (a=0.05). 
Results 
The final number of otoliths on which increments 
were counted successfully was 78 for sagittae (21% 
and 24% of otoliths were excluded from aquarium 1 
and 2, respectively) and 74 for lapilli (28% and 23% 
of otoliths were excluded from aquarium 1 and 2, 
respectively). 
The mean otolith length at hatching was 58.1 pm 
(SD 4.32) for sagittae (n= 30) and 39.04 pm (SD 4.04) 
for lapilli (n=30). The cores of both ototlith types were 
formed by a large number of primordia (Fig. 1). 
The number of increments deposited in northern 
pike otoliths after 7, 14, 22, and 28 days was not sta¬ 
tistically different for the 2 replications U-test, P>0.05 
for each of the 4 age groups). Therefore, the data from 
A 
40 pm 
Figure 1 
Images of otoliths at time of hatching of larval northern pike 
(Esox lucius) reared in a laboratory in 2015 at the Center of 
Aquaculture and Ecological Engineering, University of Warmia 
and Mazury in Olsztyn, Poland: (A) sagittae and (B) lapilli. 
Three examples are shown for each type of otolith. 
the replications were pooled for further analysis. The 
number of increments on otoliths, both sagittae (n=78) 
and lapilli (n=74), corresponded to the known age of 
the larvae, as was confirmed by fitting linear regres¬ 
sion to the increment number-at-age data (Fig. 2). The 
35 - 
30 - 
35 - 
Sagittae g 30 
Lapilli g 
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. S 20 
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Age (days) Age (days) 
Figure 2 
Number of increments counted from sagittae (n= 78) and lapilli (n= 74) of known- 
age laboratory-reared larval northern pike (Esox lucius). The data are described 
with linear regressions: sagittae, y=0.972x+0.69, coefficient of multiple determina¬ 
tion (R 2 )=0.98, P< 0.001; lapilli, y= Q.977x + 0.53, R 2 = 0.97, PcO.001). The slopes of 
the regressions are not statistically different from one, confirming the daily peri¬ 
odicity of increment formation. 
