Peters and Schmidt: Age and growth of larval and early juvenile Scomberomorus maculatus 
535 
(late stage of increment formation) was plotted 
separately from the mean SMI of otoliths whose 
margin was bordered by an opaque zone (early 
stage of increment formation) (Fig. 5). The ob- 
served separation in the stage of increment for- 
mation would be expected if initiation of incre- 
ment formation occurred between 1613 h and 
2330 h. 
Age and growth 
Otolith radii measurements revealed no signifi- 
cant difference between right and left lapilli 
(paired sample Gtest, P=0.127). The relation 
between SL versus lapillus radius was described 
by the following regression equation: 
SL = -4.78 + 0.68 (Radius) [r 2 =0.99, n=364]. 
No significant difference was found between 
increment counts for left and right lapilli (paired 
Gtest, P=0.190). Therefore, if left and right 
counts differed, the otolith whose increments 
were more clearly defined, or which was in better 
condition, was used to assign an age to the fish. 
Growth in young Spanish mackerel was quite vari- 
able within age classes, particularly in juveniles older 
Table 1 
Mean standardized marginal increment (MSMI), range, standard 
deviation for left (L) and right (R) lapilli, and size range for 
S. maculatus captured from 1613 to 2211 h and 1755 to 2330 h. 
Lapilli with opaque margins are considered separately from lapilli 
with translucent margins. ( n refers to the number of specimens, 
no. refers to the number of right or left lapilli.) Hours are those 
of eastern daylight time. 
Lapilli from fish Lapilli from fish 
collected 1613-2211 h collected 1755-2300 h 
Opaque Translucent Opaque Translucent 
R 
L 
R 
L 
R 
L 
R 
L 
n 
34 
10 
No. 
18 
18 
16 
16 
6 
6 
2 
4 
MSMI 
0.19 
0.22 
0.88 
0.86 
0.25 
0.23 
0.75 
0.75 
SD 
0.05 
0.07 
0.08 
0.15 
0.06 
0.05 
0.07 
0.13 
Range 
Size range 
0.3 
0.2 
0.3 
0.5 
0.1 
0.1 
0.1 
0.3 
(SLMmm) 
17.1-97.0 
22.6- 
-79.0 
than 23 days (Fig. 6). Nonlinear regression analysis 
provided the following growth equation: 
In SL = 6.2 - 55.1/Age. 
Figure 4 
Lapillus of an 18-day-old juvenile Spanish mackerel (18.7 mm SL). Note occurrence of subdaily 
rings as the fish ages. A daily growth increment (d) and a presumed subdaily increment (sd) are 
indicated. 
