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Growth, sex ratio, and maturation rate with age in the blackspot tuskfish Choerodon schoenleinii in waters off Okinawa Island, southwestern Japan

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  • Okinawa Marine Fisheries Technology Center

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The growth, sex ratio with age, and age at sexual maturation were determined based on sectioned otoliths in 257 specimens of the blackspot tuskfish Choerodon schoenleinii collected in waters off Ryukyu Island. Opaque rings observed by reflected light in the sectioned otoliths were found to form once a year from January to July. The three growth parameters of the von Bertalanffy growth equation were L∞=68.1 (cm), k=0.263, and t 0=−0.023 (year). The age at which the sex ratio reached 50% by sexual transition was about 6.15years, and the age at which 50% of females were sexually mature was approximately 2years. The oldest specimen among the samples was 17years old. Keywords Choerodon schoenleinii -Otolith-Growth-Sex ratio with age-Okinawa
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ORIGINAL ARTICLE Biology
Growth, sex ratio, and maturation rate with age in the blackspot
tuskfish Choerodon schoenleinii in waters off Okinawa Island,
southwestern Japan
Akihiko Ebisawa Kiyoaki Kanashiro
Toshihiko Kiyan
Received: 21 December 2009 / Accepted: 1 April 2010 / Published online: 15 May 2010
ÓThe Japanese Society of Fisheries Science 2010
Abstract The growth, sex ratio with age, and age at
sexual maturation were determined based on sectioned
otoliths in 257 specimens of the blackspot tuskfish
Choerodon schoenleinii collected in waters off Ryukyu
Island. Opaque rings observed by reflected light in the
sectioned otoliths were found to form once a year from
January to July. The three growth parameters of the von
Bertalanffy growth equation were L
?
=68.1 (cm),
k=0.263, and t
0
=-0.023 (year). The age at which the
sex ratio reached 50% by sexual transition was about
6.15 years, and the age at which 50% of females were
sexually mature was approximately 2 years. The oldest
specimen among the samples was 17 years old.
Keywords Choerodon schoenleinii Otolith Growth
Sex ratio with age Okinawa
Introduction
The blackspot tuskfish Choerodon schoenleinii is a large
labrid species distributed in the tropical western Pacific
region [1]. Because the species is commercially important,
many studies on its settlement area, growth, and feeding
behavior from the larval to juvenile stages [2,3], repro-
ductive cycle, sexual maturation, and sexual transition
based on body size [4] have been carried out in Okinawa,
southwestern Japan. Because of the species’s importance,
stock enhancement is being tried [5]. Studies of home
ranges and diel movement patterns [6], and otolith micro-
structure [7] using hatchery-reared individuals have also
been carried out. According to these studies, the species
exhibits protogynous hermaphroditism in accordance with
changes in body color, like many other labrid species.
Juveniles of the species inhabit sea-grass beds in the
innermost areas of relatively large gulfs. The major habi-
tats of the species in its adult stages are also restricted to
the adjacent regions [8]. The major habitat of the Japanese
species is very similar to that of the species in Australia,
and extensive research into reproductive biology, sexual
transition, growth [9], and habitat portioning [10] have also
been carried out at Shark Bay, a large gulf on the west
coast of Australia, where only recreational fishing of the
speces has been conducted [9].
The species is caught primarily by night spire fishing,
which captures the target after confirmation of the species
and body size. The characteristics of the fishing gear itself
allow only those fish within the size limit of the target
species to be captured. A local rule restricting the capture
of this species [heavier than 1 kg body weight; approxi-
mately 36 cm total length (L
T
)] has been established at the
northern area of Okinawa Island. The annual catch of the
species in Okinawa prefecture in the past two decades has
fluctuated between 20 and 40 mt, however, no decreasing
trend has been observed (Ebisawa, unpublished data). The
peaked body size in catch at about 28 cm L
T
, in areas
where the body-size restrictions have not been introduced,
A. Ebisawa (&)K. Kanashiro T. Kiyan
Okinawa Prefectural Fisheries and Ocean Research Center,
1-3-1 Nishizaki, Itoman, Okinawa 901-0305, Japan
e-mail: ebisawaa@pref.okinawa.lg.jp
Present Address:
K. Kanashiro
Okinawa Prefectural Sea Farming Center,
853-1 Oohama, Motobu, Okinawa 905-0212, Japan
Present Address:
T. Kiyan
456-1 Tomigusuku, Tomigusuku,
Okinawa 901-0241, Japan
123
Fish Sci (2010) 76:577–583
DOI 10.1007/s12562-010-0244-4
seems to be too smaller for the species which attains at
about 70 cm L
T
at the maximum; thus, the stock is deter-
mined to be non-rationally used even decrease in catch is
not observed (Ebisawa, unpublished data).
For stock assessments or to determine the effect of stock
management, analyses based on the age composition in the
catch are necessary, and it is important to carry out growth
studies and to examine the relationship between sexual
maturation/transition and age. The present study reveals the
growth of the species based on sectioned otoliths and
analyzes the relationship between age and sexual matura-
tion/transition, primarily using specimens from the same
source as a previous study [4] with additional specimens
collected thereafter. The results are compared to those of
Shark Bay populations in order to elucidate the biological
profiles of the species under different environments.
Materials and methods
The specimens for this study were 247 individuals among
289 specimens collected from 1986 to 1990 [4], and 35
newly collected specimens gathered from 2000 to 2006.
The major fishing sites of the specimens were Nakagusuku
Bay, Kin Bay, and the Haneji area of Okinawa Island
(Fig. 1). Most of the specimens were purchased from
commercial fishermen conducting night spire fishing. A
pair of otoliths (sagittae) was removed from each individ-
ual after measurement of the total length (L
T
) and body
weight (W
B
), and determination of the sex by the external
appearance of the gonad. The gonad was later prepared for
histological observation in order to determine both the sex
and the stage of ovarian maturation; these results have
already been reported by Ebisawa et al. [4]. Sex ratio (R
S
)
at each age was calculated based on the number of females
in the total, which included female, male, and
hermaphrodite individuals in each same-integer age group.
The rate of ovarian maturity (R
OM
) in each age group was
determined based on the number of mature females among
whole females obtained during the most active spawning
period, which is from February to May [4]. Maturity stages
from early peri-nucleolus to yolk vesicle were defined as
immature, and those from yolk globule to atretic were
defined as mature. The smallest two specimens, otolith
observations of which appear in the ‘Results’ section, are
excluded from these analyses owing to the lack of histo-
logical observations of their gonads.
Preparation and observation of otoliths
Each otolith was embedded in epoxy resin, transversely
sectioned about 450 lm thick with the core included,
mounted on slide glass with a medium (Eukitt; O. Kindler)
and covered with a cover glass. Reflected light observation
with a binocular microscope revealed translucent and
opaque zones alternating around a central opaque area
(Fig. 2a). The opaque zones outside of the central opaque
area were counted as growth rings; the observer was
blinded to the details of the specimen (body size, month
collected, sex). Whether the outermost edge was opaque or
translucent was also determined. Otolith pictures were
recorded at the first observation using a Polaroid PDMC-Ie
with 160091200 pixels and 24-bit color. A second obser-
vation was carried out by the same reader based on the
otolith picture without the reader being provided with the
previous data. When the number of growth rings matched
between the first and second readings, no further readings
were carried out; when the numbers disagreed, two addi-
tional readings from the otolith picture were performed.
When a total of three readings agreed, the number of
growth rings was considered to be determined; if three
concurring readings were not obtained, the otolith was
excluded from later analysis. Measurements of the otolith
Fig. 1 Map of the Okinawa Islands with 200-m depth contour, and
the locations where the specimens were collected
Fig. 2 Sectioned otolith of Choerodon schoenleinii from aa 46.2 cm
L
T
specimen collected January 11, 2002; bthe smallest specimen,
9.2 cm L
T
, collected January 1, 2005; and ca 10.6 cm L
T
specimen
collected May 4, 2005. All magnifications are equal, as shown by the
1-mm scale bar. The innermost four growth rings in aare identified
by a line and a number.eOuter edge of the otolith, D1 point at which
the marginal growth index was obtained
578 Fish Sci (2010) 76:577–583
123
growth ring for the analysis of the marginal growth index
(MGI) were conducted at the second reading from otolith
pictures. MGI was calculated as X0/X1 where X0 is the
distance from the start of the outermost growth ring to the
outer edge of the otolith (distance between lines ‘‘4’’ and
‘e’’ in Fig. 2a) and X1 is the distance from the start of the
inner growth ring to the outer edge of the previous trans-
lucent zone (distance between lines ‘‘3’’ and ‘‘4’’ in
Fig. 2a) at area D1 of the otolith. In case these measure-
ments at the area D1 were difficult, they were carried out at
area D2.
The age of each specimen is given as follows. Birth
month was defined as February, which is the start of the
most active spawning period of the species in the Okinawa
area [4]. The decimal part of the age is the proportion of a
year from the birth month to the month in which the
specimen was collected. Details of the growth ring for-
mation are explained further in the ‘Results’ section, but it
should be noted that the birth month is included in the
period at which growth ring is formed. Thus, the integer
part of the age is given as the number of growth rings
minus one for specimens that had a newly formed growth
ring but that were collected before the birth month (Fig. 3b,
c; dots encircled by solid line) and is given as the number
of growth rings plus one for those that had not yet started to
form new growth rings but were collected after the birth
month (Fig. 3d; dots encircled by broken line). In all other
cases, the integer part of the age is given as the number of
growth rings. Growth parameters in the von Bertalanffy
growth equation were estimated by nonlinear regression
(SPSS for Windows, release 7.5.2, SPSS) in the data sets of
age and L
T
for the specimens.
Results
Period of growth ring formation
Monthly changes in both MGI and the condition of the
otolith edge were as follows. Otoliths with translucent
edges in the single-growth-ring group were obtained con-
tinuously from July to January; their MGI values were the
lowest in July with continual increases thereafter (Fig. 3a).
In the two-ring group, otoliths with a growth ring on their
edges were obtained from January to July, and those with
translucent edges from June to January (Fig. 3b). Increases
in MGI values were continuous from the minimum values
of the otoliths with growth rings at their edges collected in
January to the maximum values of those with translucent
edges collected in December and January, in the two-ring
group. Although monthly changes in groups with three and
more rings were almost identical, earlier emergences of
otoliths with growth rings at their edges collected in
November and in December in the three-ring group were
the exception. Therefore, all otoliths with low MGI values
collected from January to July had a growth ring at their
edge, while the edges of the otoliths collected from August
to October showed a translucent zone. Thus, the growth
ring was determined to be formed annually from about
January to July.
In one of the smallest otoliths (9.2 cm L
T
), which was
obtained in January 2005, about two-thirds of the central
area was opaque (Fig. 2b), and in another specimen
MGI
0
0.1
0.2
0.3
0.4
0.5
0.6 a
0
0.1
0.2
0.3
0.4
0.5
0.6 b
0
0.1
0.2
0.3
0.4
0.5
0.6 c
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
JFMAMJJASON F
d
Fig. 3 Monthly changes in marginal growth index (MGI) in athe
single-growth-ring group; bthe two-ring group; cthe three-ring
group; and da mixed group with four and more growth rings. A solid
circle indicates an otolith with a growth ring at its edge; an open
circle indicates one with a translucent edge. The significance of the
solid and broken encircling lines is explained in the text
Fish Sci (2010) 76:577–583 579
123
(10.6 cm L
T
) obtained in May 2005, half of the central area
was opaque while the outer areas were translucent
(Fig. 2c).
Determination of age and growth parameters
Specimens whose integer ages differ from the number of
growth rings are circled in Fig. 3. Those whose integer age
is the same as the number of growth rings minus one are
circled by a solid line, including 1 specimen with two rings
collected in January (MGI =0.15: Fig. 3b), 11 specimens
with three rings gathered from November to January
(MGI \0.3: Fig. 3c), and 6 specimens with four and more
rings collected in January (MGI \0.3: Fig. 3d). Those
whose integer age is the same as the number of growth
rings plus one are circled by a broken line, including eight
specimens with four or more rings collected between
February and April (MGI [0.4: Fig. 3d). The integer ages
of all other specimens were the same as the number of
growth rings. The three parameters of the von Bertalanffy
growth equation were obtained as follows:
L1¼68:1ðcmÞ;k¼0:263;
t0¼0:023 ðyearÞðr2¼0:86Þ
Increases in body size were obvious up to 6–7 years of age,
but ceased thereafter. Body sizes of males were larger than
those of females in all same-age groups (Fig. 4).
Sex ratio and ovarian maturity rate in each age group
Average L
T
±SD for each age group, sex ratio (R
S
), and
ovarian maturity rate (R
OM
) are shown in Table 1. All
individuals aged 1 and 2 years were female. Hermaphro-
dite and male individuals appeared at 3 years of age and
older. The average L
T
of males was considerably larger
than that of females. R
S
decreased to 50% at 6 years of age,
fluctuated from 0 to 75% between 7 and 11 years of age
probably due to the small sample sizes, and decreased to
0 between 12 and 17 years. The age at which R
S
was 50%
was 6.15 years by fitting the logistic equation in R
S
of each
age class, omitting the extreme values of 0 and 75% of 7
and 11 year olds, respectively. R
OM
was 90% in 2 year
olds, reaching 100% in 3 year olds. R
OM
in 1 year olds was
not obtained because no specimens were obtained during
the most active spawning period from February to May.
Discussion
Opaque zones were found to be formed in otoliths during
the winter period in Choerodon schoenleinii, which is in
contrast to many other species, in which translucent zones
are formed during the winter period [1119]. In a previous
study using oxytetracycline (OTC) marking, in the con-
generic C. rubescens in western Australia, opaque zone
formation was determined to occur during the spring and
summer, based on the location of opaque, translucent, and
OTC marks in the otoliths, though the minute specific
analytical data for this determination were not provided
[20]. Another study found that, in the four species of the
genus Choerodon, including C. schoenleinii in western
Australia, MGI values, measured according to a baseline
defined as the outermost zones of successive opaque edges,
reach minimum in November/December [9], indicating that
translucent zone formation begins in the summer, although
Age
L
T
(cm)
0
20
40
60
80
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
male
female
hermaphrodites
Fig. 4 The von Bertalanffy growth curve fitted to observed total
length (L
T
) and age in Choerodon schoenleinii
Table 1 Average L
T
(cm) ±SD for each sex, sex ratio (R
S
), rate of
ovarian maturity (R
OM
), number of total specimens in each integer
age group (n1), and number of female specimens obtained at the
spawning period (n2)
Age L
T
(cm) R
S
n1 R
OM
n2
Female Hermaphrodites Male
1 25.6 ±3.3 1.00 41
2 32.7 ±4.5 1.00 70 0.91 11
3 41.5 ±6.1 48.0 40.5 0.96 49 1.00 13
4 46.0 ±5.0 53.6 ±3.7 54.0 ±3.1 0.70 37 1.00 12
5 49.9 ±5.3 56.5 ±3.2 57.1 ±3.3 0.73 15 1.00 4
6 53.9 ±5.9 54.7 ±0.3 58.5 ±4.3 0.50 18 1.00 3
7 64.7 59.1 0.00 2
8 55.9 52.7 61.1 ±6.2 0.20 5
9 55.4 64.7 ±3.3 0.25 4 1.00 1
10 64.8 ±8.0 0.00 4
11 55.6 ±2.4 46.7 0.75 4 1.00 2
12 69.2 ±4.8 0.00 3
13 0
14 68.3 ±6.9 0.00 2
15 72.8 0.00 1
16 64.0 0.00 1
17 76.9 0.00 1
580 Fish Sci (2010) 76:577–583
123
the author states that opaque zone formation takes place in
the summer [9]. Opaque zone formation has been con-
firmed to occur during the winter in some Labridae, such as
Thalassoma lunare, which is found in tropical eastern
Australia [21], and during the spring in three species of
Labridae in temperate eastern Australia [22]. Thus, the
opposing periods of opaque zone formation as seen in C.
schoenleinii are not specific to the labrid species.
The first growth ring is determined as the innermost
opaque band outside of the central opaque area in the
present study. In the otoliths of the two smallest specimens
obtained in the present study, a 9.2 cm L
T
specimen
obtained in January shows a translucent zone one-third of
the diameter of the otolith outside of the opaque central
area, and a 10.6 cm L
T
specimen obtained in May has a
translucent zone about half of which is outside the central
area. Accordingly, the central opaque area seems to be
formed until approximately December in specimens of
about 90 mm L
T
. Settled juveniles in the sea-grass bed
grow from about 20 mm L
T
on average in May to about
70 mm L
T
in August, and the larger individuals attain
about 100 mm L
T
by August/September [2]. Therefore, the
smallest specimen in the present study (9.2 cm L
T
,
obtained in January) clearly belongs to the 0 integer age
group, although it would have reached 1 year of age the
following February. The 10.6 cm L
T
specimen obtained in
May has to belong to the 1 integer age group even though
the first growth ring was not confirmed, since it was col-
lected after February, the designated birth month of the
species in the present study. There were no otoliths with a
growth ring at their edges in the 1 integer age group col-
lected from July to January. Thus, the first growth ring
seems to be formed during the relatively short period from
spring to early summer, shortly after the major spawning
period from February to May.
The biological parameters of age in the species of the
Okinawa population (hereafter termed Opop) differed
greatly from those of the Shark Bay population [9] (here-
after termed SBpop). The growth of Opop was significantly
faster than that of SBpop, although the maximum size and
maximum ages in the two populations were approximately
equal (Fig. 5; Table 2). While the body size at which 50%
of females reached ovarian maturity (L
OM50
) was almost
equivalent between two populations, the age of 50%
ovarian maturity (A
OM50
) was younger in Opop due to
differences in growth rate (Table 2). In addition, the great
difference in female sexual maturation between the two
populations has existed. Rate of sexual maturation in
female ranged between 40–60% at 4–8 years of age and
attained 100% at 9 and 10 years of age, although the
sample sizes at the latter two age classes are very small in
the SBpop. Therefore, A
OM50
(3.45) indicated by Fairc-
lough is obtained along with the determination of 50% of
ovarian maturation at 4–8 years of age as fully mature;
thus, about 25% of female sexually mature at 3.45 years of
age. Therefore, the A
OM50
in the SBpop become much
greater if the same criteria of A
OM50
employed in the
present study applied. In contrast, about 90 and 100% of
females at 2 and 3 years old, respectively, were sexually
mature in Opop. The age at which the sex ratio reached
50% (A
RS50
) was lower in Opop, and the number of males
out of the total number of specimens in SBpop was sig-
nificantly smaller. One of the plausible reasons for the
extremely smaller number of males in the SBpop could be
biased sampling, because only a few specimens of larger
body size were collected. However, the age of the youngest
male in the SBpop was 7 years old, whereas it was
LT (cm)
Age
0
10
20
30
40
50
60
70
024681012141618
Opop
SBpop
Fig. 5 Growth curve of Choerodon schoenleinii.Open circles
represent the Okinawa population, solid circles the Shark Bay
population according to Fairclough [9]
Table 2 Comparison of biological parameters in Choerodon
schoenleinii between the Okinawa population (Opop) and Shark Bay
population (SBpop) by Fairclough [9]
Opop SBpop
L
?
68.1 73.4
k0.263 0.111
t
0
-0.023 -0.72
Maximum age 17 16
A
OM50
\2.0 3.45
L
OM50
*24.0 25.3
A
RS50
6.15 10.37
L
RS50
54.6 55.6
L
T
of the smallest male 40.5 52.1
Age of the youngest male 3 7
Number of males in total specimens 47/289 8/575
A
OM50
and L
OM50
age and total length (L
T
) at which 50% of females
are sexually mature; A
RS50
and L
RS50
, age and L
T
at which sex ratio
reaches 50%
Fish Sci (2010) 76:577–583 581
123
extremely younger at 3 years old in Opop (Table 2). The
age of emergence of the youngest male was lower under
higher fishing pressure in comparison with the congeneric
C. venustus experiencing lower fishing pressure in adjacent
regions [23]. On the contrary, in a comparison of the body
size and age of the youngest male between two populations
of the congener C. rubescens—one experiencing low
fishing pressure and higher growth due to high productivity
at the area and the other experiencing higher fishing pres-
sure—the body size of the smallest male was smaller at the
area of higher fishing pressure. However, the age of the
smallest male was older there because of the slower growth
rate. In addition, A
RS50
was younger at the lower fishing
pressure area. These contradictory findings indicate that the
reason for the sexual and maturational differences between
SBpop and Opop can not yet be determined. The reason for
the difference seems to be linked not only to environmental
factors, such as biology, genetics, population density, food
availability, antibiotics, water temperature, and water flow,
but also artificial factors, such as fishing pressure and
methods. If the effect of the artificial factors is not small,
management strategies for the species should be developed
by that take these factors into consideration.
Assuming a normal distribution around the calculated
body size at age using the given mean square obtained
during the estimation of the growth parameters, the per-
centage falling below the size restriction (\36.0 cm L
T
)as
currently enforced at the northern area of the Okinawa
Island is 100% at 1 year, 78% at 2 years, and 22% at
3 years. In hermaphroditic species, size-selective fishing
makes the proportion represented by the second sex sig-
nificantly smaller compared to dioecious species [24,25].
If the size-at-sex-change is flexible, the side effects of size-
selective fishing are small [26,27]. In many labrid species,
a haremic social structure, in which the disappearance of
the male induces the sexual transition of the apex female
into male in the harem, has been reported [2830].
Therefore, if this type of social structure exists in C.
schoenleinii, size-selective fishing of larger individuals
does not necessarily lead to a shortage of males in the
population. The specimens in the present study were
obtained before the introduction of size-selective fishing at
the study site. This size restriction is currently conducted at
Haneji, but not yet at Kin and Nakagusuku. It is therefore
necessary to obtain growth rate, age, and body size of both
sexual maturation and sexual transition, before and after
the introduction of the body-size-restrictive fishing at Kin
and Nakagusuku areas in order to fully elucidate the effects
of size-selective fishing.
Acknowledgments This work was supported in part by the ‘‘Mor-
phometric Survey of Important Fishery Resources in Seas Adjacent to
the Okinawa Islands’’ and ‘‘Research on Biological Characters of
Dominant Species of Coral Reefs around the Okinawa Islands,’’ both
being conducted by the Japan Fisheries Agency. We are grateful to
Mr. W. Noda of the University of the Ryukyu, who kindly provided
small specimens of the species.
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... The limited shift in spatial measures for diversity is also likely to, at least partly, be explained by the long life cycles of many of the demersal species. For example, species caught in higher numbers such as the snapper Chrysophrys auratus, the West Australian Dhufish Glaucosoma hebraicum, Breaksea Cod Epinephelides armatus and Baldchin groper Choerodon rubescens are slow-growing, long-lived species (Hesp et al., 2002;Moore et al., 2007;Ebisawa et al., 2010;Parsons et al., 2014). This would result in more consistent abundances in their natural habitats than shorter-lived species whose densities are more likely to fluctuate across years. ...
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Information on fish species diversity is important to monitor changes and maintain sustainability in multispecies fisheries. However, examination of species diversity often ignores spatial patterns, yet it is influenced by spatially structured ecological processes. Such information is important for identifying areas of high conservation value for individual species, taxonomic groups or the entire ecosystem. In this study, the spatial distribution of West Coast demersal scalefish diversity in Western Australia was characterized based on recreational fishing data collected through two off-site phone-diary surveys. Using multivariate indicator cokriging, the effect of fishing effort and measurement uncertainty was considered in the characterisation. The study found that teleost species from Families Epinephelidae, Glaucosomatidae and Sparidae were the most common, with the relative contribution of 77% and 71% to the total catch in 2011/12 and 2013/14, respectively. In addition, maps of diversity indices showed that high diversity was located at the south-central parts of the study area and increased near the coast with some patchiness at the southern part. Spatial maps can be helpful when site-specific management is aimed at maintaining a certain level of species diversity caught by recreational fishers.
... If two or all three counts were the same, that number was designated as the number of opaque zones on the otolith. The first growth ring was determined to be the innermost opaque band outside of the central opaque area (Ebisawa et al. 2010). The average percent error (APE; Beamish and Fournier 1981) and coefficient of variance (CV; Campana 2001) were calculated to estimate aging precision, as follows: ...
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... Shimose & Tachihara (2005) also demonstrated that the annulus formation of Lutjanus fulviflamma was related to spawning rather than to changes in seasonal water temperature. Similarly, the annulus of Choerodon schoenleinii in the south-western waters of Okinawa, Japan was formed after the end of the spawning season (Akihiko et al., 2010), indicating a possible influence of spawning. The formation of the annulus for P. anomala was between July and August, which coincides with the end of the spawning season (Wang & Chen, 1995;Wang et al., 2015). ...
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Age and growth of the Japanese butterfish Psenopsis anomala in the waters off north-eastern Taiwan–Erratum - Shyh-Bin Wang, Li-Yu Hung, Kwang-Ming Liu
... Shimose & Tachihara (2005) also demonstrated that the annulus formation of Lutjanus fulviflamma was related to spawning rather than to changes in seasonal water temperature. Similarly, the annulus of Choerodon schoenleinii in the south-western waters of Okinawa, Japan was formed after the end of the spawning season (Akihiko et al., 2010), indicating a possible influence of spawning. The formation of the annulus for P. anomala was between July and August, which coincides with the end of the spawning season (Wang & Chen, 1995;Wang et al., 2015). ...
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The catch of Japanese butterfish, Psenopsis anomala in Taiwan is greater than those of any other nation; however, the biology, particularly the age and growth, of this economically important fish species is little known. This study describes the age and growth of P. anomala based on 734 specimens (340 females, 363 males, 31 unsexed) caught by trawl fishery in the north-eastern waters off Taiwan from March 2007 to July 2008. The age of specimens was estimated by counting the growth annuli in sagittal otoliths. The periodicity of annulus deposition on otolith was estimated to be one year with opaque zone deposited between July and August based on marginal increment analysis. The maximum age for both sexes was estimated to be ~4. The female portion of the population was dominated by the 3 ⁺ age class, while the male portion was dominated by the 2+ age class. The parameters of the von Bertalanffy growth function with standard error estimated based on the observed length at age using a non-linear method are as follows: L∞ = 25.47 ± 0.65 cm, k = 0.30 ± 0.03 year ⁻¹ , and t0 = −1.84 ± 0.16 year for females ( n = 350), and L∞ = 22.39 ± 0.45 cm, k = 0.46 ± 0.04 year ⁻¹ , and t0 = −1.38 ± 0.13 year for males ( n = 378). The growth performances of P. anomala reported from different geographic regions were compared, and the potential influences of sample size distribution on the estimated growth parameters were further discussed.
... Steward et al. (2009) mentioned that ring formation in the otoliths of gray angelfish (Pomacanthus arcuatus) occurs during the spawning season. Shimose and Tachihara (2005) and Akihiko et al. (2010) also concluded that ring formation in otoliths is related to the spawning behavior of the blackspot snapper Lutjanus fulviflammus and the blackspot tuskfish Choerodon schoenleinii in the waters off Okinawa Island, Japan. For R. sarba, the spawning season occurs mainly from the end of winter to the spring but varies in different waters. ...
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Age, growth and mortality of the goldlined seabream, Rhabdosargus sarba, were estimated based on 593 and 6516 specimens that were collected in waters off southwestern Taiwan from September 2015 to August 2016, and April 2015 to December 2017, respectively. The body weight (BW) and total length (TL) relationship (all data-pooled) was expressed as: BW= 0.01511 TL3.0346 (r2 = 0.95; n = 593). Growth rings (identified as opaque and translucent zones) were counted on 447 sectioned sagittal otoliths using a microscope under transmitted light and were counted up to 8 (42.0 cm TL) for both sexes. Edge analysis indicated that growth rings in otoliths were deposited once per year, and the opaque zone was formed in December. The von Bertanlanffy growth function (VBGF) best fit the observed length at age data for R. sarba. The growth parameters (± standard error) of VBGF for R. sarba (all data-pooled) were estimated as: L∞ = 53.94 ± 3.71 cm TL, k = 0.217 ± 0.033 yr-1, t0 = -0.182 ± 0.167 yr (n = 447). Total mortality estimated from a length converted catch curve was 0.655 yr-1, age-specific natural mortality and fishing mortality were estimated as 0.789-0.293 yr-1 and 0.109-0.365 yr-1, respectively. The exploitation rate was estimated to be 0.440.
... Choerodon schoenleinii is a large labrid species reaching 1 m in total length (TL) and an age of at least 17 yr. It is distributed throughout the tropical western Pacific region, in waters up to 60 m in depth (Araga 1997, Westneat 2001, Ebisawa et al. 2010. C. schoenleinii is monoandric and exhibits ha re mic protogynous hermaphroditism, sexual size dimorphism with males being larger, and sexual dichromatism (Ebisawa et al. 1995, Fairclough 2005, Sato et al. 2018. ...
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Protogynous fishes are major components of commercial fisheries worldwide. They can compensate for fishing losses of males through socially controlled sex change. If their resiliency, however, is insufficient to compensate for male loss, their reproductive output can decline. Understanding the effects of fishing losses of males on reproductive output of stocks requires a detailed understanding of species-specific physiological constraints on sex change and gametogenesis. The potential impact of fishing losses of males on the reproductive output of the large protogynous species Choerodon schoenleinii was investigated by assessing the seasonality of male fishing pressure using market research. In addition, laboratory experiments imitating male removal from a social group through fishing were used to assess (1) whether females change sex during the spawning season, (2) the period after change that is required for an individual to become a functionally mature male, (3) whether individuals have sufficient capacity to fertilize batches of spawned eggs just after sex change, and (4) the impact of fishing losses of males on reproductive output of a social group. Following removal of males from 8 artificial social groups, only one female changed sex. The inability of most females to change sex during the spawning season and the slow rate of sex change may be closely related to the low natural mortality and long lifespan of this species. The female that changed sex showed low fertilization rates for at least 1 mo after sex change. Males are fished from stocks mainly before and during the spawning season, which will result in a large reduction in reproductive output due to male limitation and lower fertilization rates.
... The blackspot tuskfish, Choerodon schoenleinii (Valenciennes, 1839), is a large labrid species distributed in the tropical western Pacificregion (Westneat,2001).Animportanttargetspeciesforfish-eriesinsouthernJapan,itismainlycaughtbynocturnalspearfishing (Kanashiro,Motonaga,Ebisawa,&Kyan,1990;Ohta,2007;Ebisawa, Kanashiro, & Kiyan, 2010).The species exhibits monandric protogynous hermaphroditism and sexual dimorphism, with the body color changingfromaninitialgreenish-yellowphase(IP:female)toaterminalbluephase(TP:male),inalmostcompleteaccordancewiththesex transition (Ebisawa,Kanashiro,Kiyan,&Motonaga,1995 where L t isTL at age t, and L ∞ , k, and t 0 are the asymptotic length, growth coefficient, and hypothetical age atTL=0, respectively.The growth coefficient of this study was compared with those of previousstudies(Ebisawaetal.,2010).Moreover,theVBGFparametersof ...
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To better understand the plasticity of life history traits in the blackspot tuskfish, Choerodon schoenleinii (Valenciennes, 1839), the characteristics of the population around the Yaeyama Islands (24°N, 124E) were examined and compared to those around Okinawajima Island (26°N, 128E) that had been investigated in a previous study. Age and growth of the Yaeyama population were examined based on 103 specimens collected at fish markets between 2006 and 2016. Specimens included 83 females (25.2–69.0 cm total length [TL]), and 20 males (43.1–71.8 cm TL). Ages determined from sectioned otoliths ranged from 1–9 for females, and 4–15 for males. Values for von Bertalanffy growth functions were Lt = 74.2 {1−exp[−0.23 (t + 0.38)]}, and the growth of the Yaeyama population was significantly faster than that of the previously studied population. Sexual demography of the two populations was compared using body length data on landings measured at the fish markets. In the Yaeyama population, females and males ranged from 24–65 cm TL and 39–75 cm TL, respectively; length at 50% individual sex change size was estimated at 54.7 ± 0.56 cm (±95% C.I.). In contrast, in the Okinawajima population, females and males ranged from 16–65 cm TL and 30–75 cm TL, respectively; meanwhile, 50% sex change size was estimated to be 50.0 ± 0.25 cm. There were thus significant differences in the size at sex change between the two populations. This difference may be related to the difference in population density between the sites.
... Our observation of the otolith edge revealed that opaque zones were formed annually between October and March (Fig. 6). The ring-mark formation appears to be controlled by environmental and physiological factors (Beckman and Wilson, 1995), and the formation has mostly been theorized to be affected by reproductive activity and seasonal water temperature changes in Okinawan marine fishes such as Clupeidae (Uehara et al., 2009), Latidae (Shimose and Tachihara, 2006), Gerreidae (Kanak and Tachihara, 2006a,b), Lutjanidae (Shimose and Nanami, 2014;Shimose and Tachihara, 2005), Sillaginidae (Rahman and Tachihara, 2005), and Labridae (Ebisawa et al., 2010). ...
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The annual reproductivec ycle and sexualityo f Choerodons choenleiniiw ere studied histologically. The major spawning period persisted from February until May, spawning of individuals occurring almost every day during the most active period, being March and April. Relationshipsb etween TL and both Fecundity and batch fecundity were obtained. C. schoenleiniim ature as femalesa t about 24cm TL and exhibit protogynous hermaphroditism with monandric sexuality. Sex transition occurred from 40- 64cm TL, all fish larger than 65cm TL being males. C. schoenleinii s closelys exuallyd ichromatic, the body color changing from an initial greenish-yellowp hase (female) to a terminal blue phase (male), in almost complete accordance with the sex transition.
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Gag, Mycteroperca microlepis, is a large, slow-growing, protogynous grouper that probably makes annual migrations to specific locations to aggregate for spawning. During 1976-82, male gag constituted 19.6% of the sexually mature individuals taken during fishery-dependent and fishery-independent sampling along the southeast coast of the United States. A similar percentage of males was found in the Gulf of Mexico from 1977 to 1980; however, males made up only 1.9% of the population in the Gulf of Mexico during 1992. To assess the current sex ratio of gag along the southeast U.S. coast, an emergency rule was enacted by the Department of Commerce in January 1995 that required commercial vessels from North Carolina to southeast Florida to land gag with gonads intact. Histological examination of 2613 gonads of sexually mature gag collected from 18 January through 18 April 1995 revealed that 5.5% of the gag from the southeast Atlantic were male. There was a weak trend indicating that females reached maturity at a smaller size in 1994-95 than in 1976-82. Very few transitional specimens were collected during the spawning season. Most transitional individuals (79%) were taken during April through June immediately after the 1995 spawning season. Gag in spawning condition were landed during December through mid-May by fishermen working offshore from North Carolina to southeast Florida. In addition, gag in spawning condition were taken during research cruises documenting the occurrence of spawning north of Florida (off South Carolina and Georgia at depths ranging from 49 to 91 m).