Coulson et al.: Biological features of Achoerodus gouldii 
59 
Figure 1 
Sectioned otoliths of the western blue groper ( Achoerodus gouldii) with (A) 3 
and (Bi 52 opaque zones. White dots show the location of each opaque zone 
in (A) and every tenth opaque zone in (B). Scale bars = 0.5 mm. 
TL = 1.19(SL) + 7.93, 
where TL = total length; 
SL = standard length; and 
for which the value of the coef- 
ficient of determination was 0.99 
(PcO.OOl). 
Note that, because the tail of 
A. gouldii is not forked, the TL and 
fork lengths (FL) of this species are 
the same and thus the TL for this 
species can be compared directly 
with the fork lengths recorded for 
other labrid species (e.g., Choat et 
al., 2006). 
Aging methods, 
length and age compositions, 
and growth patterns 
Preliminary examination of the oto- 
liths of a wide size range of A. goul- 
dii before and after sectioning dem- 
onstrated that even the otoliths of 
small fish required sectioning to 
reveal all of their opaque zones. One sagittal otolith 
from each individual was embedded in clear epoxy resin 
and a section of ~0.3 mm thickness was cut transversely 
through the primordium with an Isomet Buehler low- 
speed diamond saw (Buehler Ltd., Lake Bluff, IL). The 
otolith sections were polished with wet and dry carbo- 
rundum paper (grade 1200) and mounted on microscope 
slides with DePeX mounting adhesive (VWR Interna- 
tional Ltd., Poole, England) and a cover slip. Electronic 
images of each section of otolith and of its peripheral 
region (at a higher magnification) were taken with trans- 
mitted light and an Olympus DP70 camera (Olympus 
Optical Co. Ltd., Tokyo, Japan) mounted on an Olympus 
BX51 compound microscope (Olympus Optical Co. Ltd., 
Tokyo, Japan). These images were used for counting 
opaque zones and measuring the distances required for 
marginal increment analysis, respectively. All images 
were examined by using Leica Image Manager 1000 
(Leica Microsystems, Heerbrugg, Switzerland), which 
enabled the well-defined opaque zones (Fig. 1) to be 
marked and automatically counted and the distances 
required for marginal increment analysis to be mea- 
sured precisely. 
Validation that a single opaque zone is formed an- 
nually in the otoliths of A. gouldii was carried out by 
analyzing the trends exhibited throughout the year by 
the marginal increment on the otoliths, i.e., the dis- 
tance between the outer edge of the single or outermost 
opaque zone and the otolith periphery. The marginal 
increment was expressed as the proportion of the dis- 
tance between the primordium and the outer edge of the 
opaque zone, when one such zone was present, or as the 
proportion of the distance between the outer edges of 
the two outermost opaque zones when two or more such 
zones were present. All distances, which were recorded 
to the nearest 0.01 mm, were measured on the anterior 
surface of the otoliths and along the same axis as and 
perpendicular to the opaque zones. 
The opaque zones on the anterior surface in an im- 
age of each sectioned otolith were counted on three 
different occasions. The three counts were the same in 
91.0% of otoliths with <20 opaque zones and 70.4% of 
those with >20 opaque zones. In the case of each otolith 
for which the three counts were not the same, if two of 
those counts were the same, these counts were the ones 
recorded for aging. The numbers of opaque zones in 150 
otoliths from a wide size range of fish were counted by a 
second and experienced otolith reader (S. A. Hesp) and 
compared with those recorded by the senior author. The 
counts of 70 of the 100 otoliths with <20 opaque zones 
were the same and, where there were discrepancies, 
they differed by only 1 in 28 of the otoliths and 2 in the 
other two otoliths. For the 50 otoliths containing >20 
opaque zones, the counts were the same or differed by 
1 in 34 of those otoliths and differed by no more than 
2 in a further seven otoliths. The maximum difference 
in the counts for otoliths with >20 opaque zones was 
4. Following discussions between the two readers, it 
became apparent that the main reason for discrepan- 
cies in counts was due to the first reader, who through 
his extensive experience of examining the otoliths of A. 
gouldii, was able more consistently to detect the first 
zone. The level of agreement between the counts of the 
two readers was therefore high when his experience in 
detecting the first zone was taken into account. 
Each fish was assigned an age based on its date of 
capture, the number of opaque zones in its otoliths, the 
time of year when newly formed opaque zones become 
