122 
Fishery Bulletin 115(1) 
100 
ra 
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o 
80 - 
60 - 
40 
20 - 
0 - 
Males 
Females 
Unknown sex 
Fitted VBGM 
^ • m 
7. •• • 
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0 60 120 180 240 300 360 420 480 540 
Number of presumed daily growth increments 
Figure 4 
The combined (sex and location) von Bertalanffy growth model (VBGM) 
of roosterfish (Nematistius pectoralis) captured in Baja California Sur, 
Mexico, in 2010-2015 and in Golfo Dulce, Costa Rica, 2013-2014. 
value of b is between 2.8 and 3.2, growth 
is considered to be isometric (i.e., growth 
of all body parts is consistent and pro- 
portional throughout development). Based 
on t-test results, estimated b values were 
not significantly different from 3 (Table 1), 
indicating that isometric growth for roost- 
erfish is independent of location and sex. 
Because we did not identify differ- 
ences in the LWR, samples were pooled 
and collectively presented (see Froese, 
2006). A similar b value was reported by 
Gonzalez-Sanson et al. (2014) for rooster- 
fish caught in a coastal lagoon off Barra 
de Navidad, Jalisco, Mexico. However, the 
Gonzalez-Sanson et al. (2014) study was 
based on a limited sample size and size 
range of fish (6=2.92, n=8; 7.5-29.3 cm 
in total length). Values of the exponent 
6 can be influenced by statistical proce- 
dure and sample size (Bolger and Con- 
nolly, 1989), as well as by variations as- 
sociated with size range, maturation, sex, 
and time of year (Cone, 1989). Because 
the spawning dynamics of this species 
(i.e., season and time of year) remain 
unknown and we were unable to obtain 
samples from exceptionally large indi- 
viduals, it is possible that differences in 
LWR exist for larger, mature roosterfish. 
Age and growth 
The sagittal otolith is the preferred hard structure for 
estimating age in fish because deposition occurs con- 
tinuously throughout life, a scenario that enhances age 
estimation when compared with the use of other hard 
structures (Campana and Thorrold, 2001). Otoliths are 
also preferred for age estimation because the struc- 
tures are not lost or shed (as they are with scales) or 
reabsorbed (as with bones and spines) (Ramirez-Perez 
et al., 2011). Sectioned and polished otoliths from in- 
dividuals <57 cm FL provided visible DGIs that were 
readily distinguishable. However, in otoliths from 
larger individuals (>57 cm FL), it was difficult to dif- 
ferentiate between recent outer edge DGIs, thus caus- 
ing increased uncertainty in age estimates. Campana 
(1999) reported that calcium, oxygen, and carbon domi- 
nate the elemental composition of the otolith and that 
these elements form the calcium carbonate matrix of 
the otolith. An excess of calcium carbonate in sagittal 
otoliths may hinder ridge quantification to varying de- 
grees (Hill et al., 1989). 
In cross sections, DGIs were counted from the core to 
the dorsal edge of the otolith. The path of visual counts 
were not always in a straight line from the core to the 
outer edge of a sagitta. The optimal reading path that 
provided the best visual clarity of DGIs typically fol- 
lowed a somewhat circuitous route that shifted from one 
area of the sagitta to another (Uchiyama et al., 1986). 
The precision of age estimates for the 2 readers of 
this study was high (CV=9.02%) and aligns with CV 
values from other studies in which counts of annual 
marks were used (Prince et ah, 1991; DeMartini et ah, 
2007). Campana (2001) proposed that there is no a pri- 
ori value of CV that can be assigned as a target level 
for studies of age because it is highly influenced by 
the species and the nature of the hard structure itself 
In addition, the consistency between readings often de- 
creases as fish age increases because growth marks are 
closer together in older fish (Steward et ah, 2009). 
We found that the precision of DGI counts decreased 
with increasing age (18-548 d) and FL (5.2-86.0 cm). 
Prince et al. (1991) suggested that estimating the age 
of large or old fish by using DGI counts may result in 
an underestimation of age and an overestimation of the 
growth rate. Because it was not possible to count DGIs 
precisely in roosterfish >86 cm FL (1.5 years old), it is 
recommended that otolith DGIs be used only for indi- 
viduals of ages less than 1 year (the age reached at a 
size of approximately 66 cm FL). 
Although it was not possible to detect annual marks 
on the otoliths of roosterfish in our study, a previous 
study had focused on assessing the potential use of 
dorsal spines for aging this species (Chavez-Arellano, 
2016). Chavez-Arellano (2016) analyzed roosterfish be- 
tween 14 and 133 cm FL and found a similar average 
length (70.61 cm FL) for year-1 individuals. However, 
