MARINE AND FISHERY SCIENCES 36 (1): 17-30 (2023)
ABSTRACT. The red flounder Paralichthys orbignyanus is a large pleuronectiform fish endemic
in coastal waters, coastal lagoons and estuaries in the southwestern Atlantic. Although less abundant
than other Paralichthys spp., its high price makes it a valuable resource for small-scale fishers that
have been intensely fished in the last decades. To study its growth and lifespan in southern Brazil,
we examined thin otolith sections collected for age determinations of both young-of-the-year
(YOY) and older fishes. Opaque bands form mainly in spring and summer, coincident with the
reproductive season. Larger and older males reached 601 mm and eight years, while females
reached 985 mm and 11 years. The assumed daily microincrements counts ranged from 127 to 196
for YOY of 135 to 184 mm TL. The common weight-length equation for grouped sexes was TW♀♂
= 0.000015TL2.93 (mm, g). The von Bertalanffy growth equations were: TL= 1,076(1–e–0.15 (t+0.78));
TL= 652(1–e–0.28 (t+0.48)); and TL♀♂ = 839(1–e–0.20 (t+0.67)). Therefore, P. orbignyanus is a fast-grow-
ing and relatively short-living species for which females attain larger length and older ages than
males, characteristics that have to be taken into account for its stock assessment and management.
Key words: Fisheries, management, microincrements, population dynamics, southwestern Atlantic.
Edad y crecimiento del lenguado Paralichthys orbignyanus (Teleostei: Pleuronectiformes) en el
sur de Brasil
RESUMEN. El lenguado Paralichthys orbignyanus es un pez pleuronectiforme de gran tamaño,
endémico de aguas costeras, lagunas costeras y estuarios del Atlántico Sudoccidental. Aunque
menos abundante que otros Paralichthys spp., su alto precio lo convierte en un recurso valioso para
los pescadores artesanales que los han pescado intensamente en las últimas décadas. Para estudiar
su crecimiento y edad en el sur de Brasil, examinamos secciones delgadas de otolitos para realizar
determinaciones de edades tanto de juveniles menores a un año como de peces más viejos. Las ban-
das opacas se forman principalmente en primavera y verano, coincidiendo con la época reproducti-
va. Los machos más grandes y mayores alcanzaron los 601 mm y los ocho años de edad, mientras
que las hembras alcanzaron los 985 mm y los 11 años. Los recuentos de microincrementos diarios
asumidos oscilaron entre 127 y 196 para los juveniles de 135 a 184 mm TL. La ecuación peso-lon-
gitud para sexos agrupados fue TW♀♂ =0,000015TL2.93 (mm, g). Las ecuaciones de crecimiento de
von Bertalanffy fueron: TL=1.076(1–e–0.15 (t+0.78)); TL=652(1–e–0,28 (t+0,48)); y TL♀♂ =839
(1–e–0.20 (t+0.67)). Por lo tanto, P. orbignyanus es una especie de crecimiento rápido y vida relativa-
mente corta, cuyas hembras alcanzan mayor longitud y edad que los machos, características que
deben tenerse en cuenta para la evaluación y gestión de su población.
Palabras clave: Pesquerías, ordenación, microincrementos, dinámica de población, Atlántico
Received: 8 September 2022
Accepted: 6 October 2022
ISSN 2683-7595 (print)
ISSN 2683-7951 (online)
Journal of the Instituto Nacional de
Investigación y Desarrollo Pesquero
This work is licensed under a Creative
Commons Attribution-
NonCommercial-ShareAlike 4.0
International License
Marine and
Fishery Sciences
Age and growth of the red flounder Paralichthys orbignyanus (Teleostei:
Pleuronectiformes) in southern Brazil
1Laboratório de Recursos Pesqueiros Demersais, Instituto de Oceanografia, Universidade Federal do Rio Grande, Av. Itália km 8,
96203-000 - Rio Grande, Brazil. 2Programa de Pós-graduação em Oceanografia Biológica, Instituto de Oceanografia, Universidade Federal do
Rio Grande, Av. Itália, km 8, 96203-000 - Rio Grande, Brazil. ORCID Manuel Haimovici,
Eidi Kikuchi
The Brazilian or red flounder, Paralichthys
orbignyanus (Valenciennes, 1839), is a medium to
large-sized benthic pleuronectiform fish endemic
to the Warm Temperate southwestern Atlantic bio-
geographic province (Spalding et al. 2007), with a
continuous distribution between Rio de Janeiro
State in Brazil (22° S) and the gulf of San Matías
in Argentina (41° 30' S) (Cousseau and Perrotta
1998; Menezes et al. 2003). It is a euryhaline
species that inhabit shallow coastal marine waters
and estuarine environments (Chao et al. 1985;
Haimovici et al. 1996; Rivera Prisco et al. 2001;
Diaz de Astarloa 2002; Lopez Cazorla 2005).
Paralichthys orbignyanus was commercially
fished in the Patos Lagoon and nearby coastal
waters in southern Brazil, and used by the can-
ning industry of the city of Rio Grande by the late
XIX century (Odebrecht 2003). It is still fished by
small-scale fishers in the region, mainly by dou-
ble rig bottom trawlers but also with bottom gill-
nets (Haimovici and Mendonça 1996; Haimovici
and Cardoso 2017). No reliable specific landing
statistics are available for the red flounder, as it is
rarely discriminated from other flounders (i.e. P.
patagonicus and P. isosceles) in southern Brazil.
However, reported landings of flounders by small
scale fishers in Rio Grande, among which P.
orbignyanus is dominant, decreased from a few
hundred tons in the 1980s to less than 50 t in the
2000s (CEPERG 2012), suggesting its overfish-
ing. This stock reduction perspective scenario
was supported by long-term perceptions of red
flounders catches by small-scale fishers in the
Patos Lagoon (Thykjaer et al. 2019). In addition,
there is an overall trend of overfishing of demer-
sal fishes from the Patos Lagoon and the inner
shelf along southern Brazil, among which the red
flounder is not expected to be an exception
(Haimovici and Cardoso 2017).
Some aspects of the life history of P. orbig-
nyanus in its natural environment have been stud-
ied in southern Brazil. The species has a long
reproductive season between spring and summer
since fully developed intraovarian oocytes and
high gonadosomatic indices were observed
between October and March (Carneiro 1995; Sil-
veira et al. 1995; Robaldo 2003). Experimental
studies showed that eggs only hatch at seawater
salinities; therefore, their spawning is assumed to
occur in coastal marine water, but the small
pelagic larvae rapidly acquire the capacity to
withstand low salinities, allowing them to colo-
nize brackish waters (Sampaio et al. 2007). This
capacity allows them to occupy nursery grounds
in estuaries, coastal lagoons and brackish surf
zone coastal waters, early on in life. In the Patos
Lagoon estuary, juvenile red flounders feed main-
ly on polychaetes, preadults and adults feed main-
ly on small fish, brachyuran crabs, tanaidaceans,
miscidacean, and small penaeid shrimp, while
larger specimens feed both in the estuary and
coastal waters mainly on small fishes and penaeid
shrimp (Carneiro 1995).
Large size P. orbignyanus tolerance to low
salinities and of high commercial value, led to
studies of its potential for aquaculture in Brazil
(Wasielesky et al. 1994; Sampaio and Bianchini
2002) and Argentina (Radonic et al. 2007). Its
individual growth in the environment has been
studied in the southern limit of its distribution, in
the Bahia Blanca region in Argentina, based on
age determinations on scales (Lopez Cazorla
2005) but not in southern Brazil, where the
species is an important component of the estuar-
ine and coastal shallow waters fish communities.
The lack of basic information on population
dynamics of P. orbignyanus led to it being con-
sidered ‘data deficient’ in the IUCN Red List of
Threatened Species (Riestra et al. 2020). In this
study, the growth and longevity of P. orbignyanus
in southern Brazil were estimated to contribute to
filling this gap. For this purpose, ages were deter-
mined based on the interpretation of both
microincrements in the otoliths of young-of-the-
18 MARINE AND FISHERY SCIENCES 36 (1): 17-30 (2023)
year and seasonal bands in the otoliths of
subadults and adults. Otoliths grow along the life
of fishes by the apposition of layers of proteins
and salts that form layers of different optic densi-
ties both on a daily (microincrements) and sea-
sonal (annuli) basis (Morales-Nin 2000; Green et
al. 2009). The combined interpretation of bands
formed in otoliths of juveniles and adults can
contribute to the validation of the periodicity in
the formation of the annuli (Cavole and Haimovi-
ci 2015; Cavole et al. 2018). Life-history param-
eters of age and growth obtained in this study are
expected to be useful in future assessment models
needed to define desirable states for appropriate
fishery management.
Sampling sites
Overall, otoliths of 224 specimens collected
between 1989 and 2000 from small-scale gillnet
fishing in the estuary of the Patos Lagoon and
commercial bottom trawling and research surveys
in coastal waters (<25 m) along southern Brazil
were examined (Figure 1).
Total weight (TW, g) and total length (TL, mm)
measured from the tip of the snout to the mid-
point of the caudal were recorded before the dis-
Figure 1. Estuarine and coastal regions along southern Brazil from where samples of Paralichthys orbignyanus were collected.
section of each specimen. Gonads from each fish
were weighed (g) and examined visually for sex
determination, and sagittae otoliths were extract-
ed and preserved dry for age determination.
Age determinations
Thin transverse sections (0.20-0.30 mm) of
right sagittal otoliths were cut through the nucle-
us and embedded in polyester resin using a low-
speed rotary saw (Buehler-Isomet). All sections
were fixed on glass slides with xylol (dimethyl-
benzene) base mounting media (ENTELAN
Merck®). Sections were examined with transmit-
ted light under a stereoscopic microscope (× 10).
Digital images of otolith sections (Figure 2) were
obtained using a stereoscopic microscope at × 10
objective power on a camera with 2048 ×1536
pixels. Distances between the otolith core and the
end of opaque bands assumed a priori as annuli
(annual bands), were measured with the free soft-
ware ImageJ 1.47 (
On the transverse sections, alternate opaque
and translucent bands were counted independent-
ly by two readers. If counts differed, otoliths were
read again by both readers and discarded from
further analyses if the difference persisted. The
periodicity of the formation of opaque and
translucent bands on the edge of otoliths were
evaluated by counting monthly opaque and
translucent edges. Microincrements counted in
the transverse sections of sagitta otoliths of four
young-of-the-year measuring 135 and 184 were
used to fit the von Bertalanffy growth curve along
the first year of life with the annulus observed for
older fishes. Otoliths were prepared and polished
following the method described by Cavole and
Haimovici (2015). Microincrements were count-
ed between the otolith core and the outer edge of
the otolith along the ventral axis (Figure 3).
Back calculations
To back-calculate the total length at each age,
the procedure proposed by Campana (1990) was
followed, which assumes a linear relationship
between the fish length (L) and the radius of the
otolith length (R) with a fixed intercept (biologi-
cal intercept) for all analyzed individuals. This
procedure assumes that the greatest variation
between R and L of individual fishes occurs in the
slope of the relationship and not in the hypotheti-
cal value of the radius for fishes at zero length, as
shown in several experiments of controlled or
manipulated individual fish growth (Vigliola and
Meekan 2009).
20 MARINE AND FISHERY SCIENCES 36 (1): 17-30 (2023)
Figure 2. Thin transverse section of a six years old and 750 mm female Paralichthys orbignyanus from southern Brazil examined
with transmitted light. Black letters indicate the nucleus (N), the end of each opaque band (Ri) and the border (Rt).
A radius of 0.0789 mm (R0) measured on a sec-
tioned otolith from a juvenile 135 mm total length
(TL0) was considered as the biological intercept.
Back-calculated lengths were obtained according
to the following equation:
TLi=TLc+(RiR0). (TLcTL0) (RcR0) 1
where TLiis the back-calculated length-at-age i;
TLcis the total length of the fish at the time of
capture; Riis the radius of the otolith at a given
age i; and Rcis the total inner radius of the otolith
at the time of capture.
Growth analyses
Growth in length was described by the von
Bertalanffy growth model (VBGM) from back-
calculated mean lengths-at-age for each sex as
TL =(L1ek(tt0))
where TL is the total length-at-age tof the fish
from the tip of the snout to the end of the upper
limb of the tail in a normal position; Lis the
asymptotic length; kis the growth coefficient,
which represents the rate at which the fish length
approaches L; and t0is the theoretical age at
which the fish would have a length of zero. The
fit of the model to the data was performed with a
Bayesian approach (Kinas and Andrade 2010).
Age-length data were assumed to follow a log-
normal distribution: yi= logN(μi, σ2) where yiis
the length distribution, μiis the mean length for
each age class i, and variance σ2. A logarithmic
version of the VBGM was used for computational
convenience as follows:
μi=log(L)+ log(1k(it0))
Seed values for each parameter were constructed
from a non-informative prior with wide distribu-
tion intervals. The probability of log k was con-
sidered to follow a normal distribution with a
mean of zero and variance equal to 0.001 and
restricted to the interval of −5 and 5. The proba-
bility of log Lwas considered to follow a normal
distribution with a mean equal to the logarithm of
the observed maximum L and a variance of 0.001.
The probability of t0was considered to follow a
uniform distribution with a minimum equal to −3
Figure 3. Thin transverse section of a 153 mm juvenile
Paralichthys orbignyanus from southern Brazil with
137 microincrements. White circles indicate some of
the microincrements counted from the core. Scale
black bar is 0.1 mm.
and a maximum equal to zero. The probability of
σ was considered to follow a uniform distribution
with a minimum equal to zero and a maximum
equal to five.
Posterior distributions of parameters were
obtained through the stochastic process of Monte
Carlo Markov chains (MCMC), which provides
an easy and clear way to compare the resulting
parameters by analyzing the overlap between pos-
terior probability distributions. In a single chain,
31,000 iterations were generated with a burn-in of
the first 10,000 values and removal of one of the
two remaining values, resulting in a final sample
with 10,500 values in the posterior distribution of
each parameter (Kinas and Andrade 2010). These
analyses were performed using the OpenBUGS
package and the libraries R2 WinBUGS (Sturtz et
al. 2005) and BRugs (Thomas et al. 2006). All sta-
tistical analyses were performed in R software (R
Core Team 2022) version 4.2.1.
Weight-length relationship
The relationship between weight and length
was described by the potential model (TW α=
TLb). Data were transformed into decimal loga-
rithms for comparisons and linear regression
models were compared between sexes through
covariance analysis (α=0.05) (Zar 1984). The
asymptotic weight (W) was estimated by trans-
forming length by age data to weight-by-age data,
based on potential weight-length equations.
Otoliths of 224 specimens between 266 to 985
mm TL were examined by two independent read-
ers (MH, EK) for alternate opaque and translu-
cent bands. The thickness, curvature, height of
the crista, and optic density of otoliths were vari-
able, resulting in considerable differences in the
visualization of the width of opaque bands. How-
ever, the two readers counted the same number of
opaque bands in the otoliths of 171 specimens
(76.3%). In a second joint reading, an agreement
was reached for other 30 otoliths that differed
only in one opaque band. An inconsistent pattern
of opaque bands or higher count differences was
observed for 23 otoliths (10.3%). Overall, ages
were attributed to 89.7% of specimens, 70 males
and 131 females.
Validation of age determinations
Opaque edges in sectioned otoliths occur year-
round, with their relative frequency increasing
sharply from 29% in September to 83% in Octo-
ber and 92% in December and gradually decreas-
ing to 14% in May (Figure 4). Although confi-
dence intervals among many months overlapped,
the percentage of opaque bands between October
and March was significantly higher than between
April and September (χ2 (1; N =224) =42.7, p <
0.001), giving support to the hypothesis that each
year one opaque was primarily formed in spring
and summer, and a translucid band mostly in
autumn and winter.
Ages were assigned to each fish according to
the number of opaque bands (annuli) on otoliths.
The midpoint of the period with higher propor-
tions of opaque bands in the edge of sections of
otoliths was between December and January. It
was also approximately the midpoint of the peri-
od in which higher gonadosomatic indices
(Carneiro 1995; Robaldo 2003) and hydrated
oocytes were observed in ovaries (Silveira et al.
1995). Therefore, 1st January was considered the
mean birthday date of all fishes and used to cal-
culate the age in fractions of years, in which the
number of opaque bands corresponded to the
number of completed years of life.
Age-length relationships
The older male attained eight years old and
measured 575 mm, while the older female had 11
22 MARINE AND FISHERY SCIENCES 36 (1): 17-30 (2023)
years and measured 830 mm. The larger sampled
male measured 601 mm and was seven years old,
while the larger female measured 985 mm and
was eight years old. Total length at capture and
back-calculated length at all ages of females were
larger than those of males, with differences in the
total length increasing from 8% at age one to
143% at age eight (Table 1).
The number of microincrements in sectioned
otoliths of four young-of-the-year specimens
measuring 135, 153, 168, and 184 mm (L) were
127, 153, 168, and 196, respectively. Microincre-
ments were considered a priori daily due to their
well-marked appearance and for presenting a
concentric pattern from the focus to the edge of
otoliths sections (Figure 3). Thus, microincre-
ments counts, transformed in fractions of years,
were used for estimations of von Bertalanffy
growth curve, helping to fit the length-at-age in
the beginning curve.
Growth analyses
Individual back-calculated length-at-age for
each sex and microincrements readings of the
four unsexed young-of-the-year were used to
calculate the von Bertalanffy’s growth parame-
ters. Credibility intervals for both Land kfor
males and females did not overlap, showing a
significant difference between sexes. Values of
t0did not differ significantly between sexes
and showed a reasonable adjustment at early
ages, with absolute values lower than one year
(Table 2).
Although a large variability of the length-at-
age was observed for both sexes, a good overall
fitting was observed between the length-at-age
observed in the catch and the growth curve esti-
mated for the back-calculated length-at-age (Fig-
ure 5). Males grew much smaller than females,
reaching only 57% of females’ L. In contrast, the
intrinsic growth rate kwas significantly larger for
males (k=0.40), and more than twice that for
females (k=0.18). The difference occurs because
of the rapid decrease in growth of males after age
3 (Figure 5; Table 1). The total length-at-age of
the four unsexed young-of-the-year forced curves
to relatively low t0values, indicating that both
male and female estimated growth curves fit well
at all ages (Figure 5).
Figure 4. Monthly percentages of opaque bands in the edge of transverse sections of otoliths of Paralichthys orbignyanus from
southern Brazil. Sampled numbers are between brackets and vertical bars represent 95% of confidential intervals.
Weight-length relationships
Total weight (g)-total length (mm) relationships
for 190 fishes between 230 to 865 mm did not dif-
fer between sexes (F =1.04; p=0.31). The relation-
ship for pooled sexes including unsexed juveniles
was W =0.000015 TL2.930, R2=0.99. The 95%
confidence limits for the slope coefficient was
2.895-2.996, therefore, for this set of data, the
growth relationship between length and weight
cannot be considered straightforward isometric.
Weight-transformed growth curves show that males
attained 36.7% of females’ weight at age eight and
that absolute yearly growth was 447 g between
ages tree and four for males and 932 g between
ages seven and eight for females (Figure 6).
24 MARINE AND FISHERY SCIENCES 36 (1): 17-30 (2023)
Table 1. Observed mean total length (TL, mm) at capture and back-calculated mean TL at age of males and females red floun-
ders Paralichthys orbignyanus, fished in southern Brazil between 1989 and 2000. n =number of sampled individuals.
Age n 1 2 3 4 5 6 7 8
1 15 266
2 26 264 378
3 17 251 366 465
4 5 230 348 443 500
5 2 239 357 453 505 540
6 1 270 400 474 520 546 575
7 3 259 377 451 514 561 597 625
8 1 258 366 441 472 509 535 554 575
Mean TL back-calculated 70 255 370 455 502 539 569 589 575
Mean TL in the catch 314 394 477 500 540 575 548 575
Age n 1 2 3 4 5 6 7 8 >
1 9 286
2 44 276 400
3 43 248 391 499
4 15 277 402 507 583
5 13 250 393 519 621 688
6 4 271 389 503 628 701 746
8 > 3 321 453 534 610 676 730 781 824
Mean TL back-calculated 131 276 405 512 610 688 738 781 824
Mean TL in the catch 335 428 515 607 691 746 808