MARINE AND FISHERY SCIENCES 36 (1): 17-30 (2023)

https://doi.org/10.47193/mafis.3612023010103

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

Sudoccidental.

*Correspondence:

manuelhaimovici@gmail.com

Received: 8 September 2022

Accepted: 6 October 2022

ISSN 2683-7595 (print)

ISSN 2683-7951 (online)

https://ojs.inidep.edu.ar

Journal of the Instituto Nacional de

Investigación y Desarrollo Pesquero

(INIDEP)

This work is licensed under a Creative

Commons Attribution-

NonCommercial-ShareAlike 4.0

International License

Marine and

Fishery Sciences

MAFIS

ORIGINAL RESEARCH

Age and growth of the red flounder Paralichthys orbignyanus (Teleostei:

Pleuronectiformes) in southern Brazil

MANUEL HAIMOVICI1, *, EIDI KIKUCHI1, 2 and CAROLINA GONÇALVES OLIVEIRA1

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 https://orcid.org/0000-0003-1741-8182,

Eidi Kikuchi https://orcid.org/0000-0002-9940-9767

INTRODUCTION

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.

MATERIALS AND METHODS

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-

HAIMOVICI ET AL.: AGE AND GROWTH OF PARALICHTHYS ORBIGNYANUS

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 (www.imagej.nih.gov).

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+(Ri−R0). (TLc−TL0) (Rc−R0) −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

follows:

TL =(L∞1− e−k(t−t0))

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; L∞is 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(1−k(i−t0))

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 L∞was 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

HAIMOVICI ET AL.: AGE AND GROWTH OF PARALICHTHYS ORBIGNYANUS

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.

RESULTS

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 L∞and 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).

HAIMOVICI ET AL.: AGE AND GROWTH OF PARALICHTHYS ORBIGNYANUS

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.

Month

Jan

(23)

Feb

(27)

Mar

(15)

Apr

(19)

May

(21)

Jun

(8)

Jul

(18)

Aug

(22)

Sep

(21)

Oct

(23)

Nov

(14)

Dec

(13)

100

Percentage

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.

Males

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

Females

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

DISCUSSION

Understanding the life history strategy of the

red flounder Paralichthys orbignyanus in south-

ern Brazil is essential to support its management,

especially the growth parameters that form part of

most fisheries assessment methods, influencing

population dynamics through its effects on life-

time patterns of biomass production, natural and

fishing mortality, and reproductive output (Fran-

cis 2015; Lorenzen 2016).

Results from the present study indicate that P.

HAIMOVICI ET AL.: AGE AND GROWTH OF PARALICHTHYS ORBIGNYANUS

Table 2. Von Bertalanffy’s growth parameters and their respective credibility interval (Cr.I, α=0.025) for the back-calculated

mean total length (mm) at age of males, females and both sexes of the red flounders Paralichthys orbignyanus, from

southern Brazil.

Males Females Both sexes

L∞ Lower Cr.I 590.5 1,045.1 845.8

Mean 612.1 1,082.7 902.8

Upper Cr.I 638.8 1,122.7 986.0

k Lower Cr.I 0.34 0.17 0.16

Mean 0.40 0.18 0.21

Upper Cr.I 0.47 0.20 0.24

t0 Lower Cr.I -0.57 -0.69 -1.11

Mean -0.35 -0.61 -0.79

Upper Cr.I -0.17 -0.54 -0.55

Figure 5. Von Bertalanffy’s growth curves for mean back-calculated total length-at-age of females (A) and males (B)

Paralichthys orbignyanus in southern Brazil. Full circles indicate the individual total length-at-age observed at capture.

Triangles indicate the four young-of-the-year for which microincrements were counted. The continuous line indicates the

regression line. The dashed line indicates the credibility interval (α=0.05).

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Age (years)

1,100

1,000

900

800

700

600

500

400

300

200

100

Total lenght (cm)

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Age (years)

orbignyanus is a fast-growing and relatively

short-living species with females showing higher

growth and attaining larger sizes and older ages

than males. The Genus Paralichthys has 20

species widespread in warm to temperate waters

on continental shelves of the world (Froese and

Pauly 2022). Ages and growth of several com-

mercially important species of this genus have

been studied, such as P. californucus from the

western US (Pattison and McAllister 1990; Mac-

Nair et al. 2001; Barnes et al. 2015); P. lethostig-

ma from the Gulf of Mexico and eastern USA

(Fischer and Thompson 2004); P. dentatus from

the eastern USA (Dery 1997); P. olivaceus from

Japan (Atsuchi et al. 2004; Yoneda et al. 2007); P.

patagonicus from southern Brazil (Araujo and

Haimovici 2000) and Uruguay to Argentina

(Riestra 2010); P. isosceles (Fabré and Cousseau

1990); and finally P. orbignyanus from Argentina

(Lopez Cazorla 2005). Among these species most

show the same growth pattern as P. orbignyanus;

however, no consistent pattern was observed in

the seasonality formation of opaque bands in

otoliths, or annuli on scales, either between dif-

ferent species or even among different stocks of

the same species. In the case of P. orbignyanus

from southern Brazil, opaque bands in otoliths

form mainly in spring and summer when gonads

mature, and the species spawn (Silveira et al.

1995). This correspondence between spawning

26 MARINE AND FISHERY SCIENCES 36 (1): 17-30 (2023)

Figure 6. Female (black) and male (grey) Paralichthys orbignyanus. A) Weight transformed von Bertalanffy’s growth curves. B)

Yearly increments in weight-at-age in southern Brazil.

1234567891011

Age (years)

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

Total weight (g)

1,000

900

800

700

600

500

400

300

200

100

Weight increment (g)

season and opaque band formation was also

observed for P. patagonicus in the same region

(Araujo and Haimovici 2000). At higher latitudes

(41° S), narrow growth bands in the edge of

scales of P. orbignyanus were observed from

autumn to spring, and only wide bands in summer

(Lopez Cazorla 2005), suggesting a similar sea-

sonal growth pattern as in southern Brazil. No

differences in the weight-length relationship was

either observed between sexes in both regions. A

similar lack of difference of the weight-length

relationship between sexes was observed for P.

lethostigma (Fischer and Thompson 2004).

Juveniles of piscivorous fishes, as those of the

genus Paralichthys, need to grow quickly to be

able to prey on other species of the same year

class in their common nursery grounds (Juanes

and Conover 1994). Therefore, it is not surpris-

ing that P. orbignyanus is a fast-growing fish,

with males attaining an average of 255 mm and

females 276 mm TL in the first year of life.

Despite that, at the age of eight, males attained

only 57% of L∞and 36% of the weight of

females. Consistent with the scientific literature,

from age three onwards, the greater size and

weight of females compared to males are evi-

dent, a pattern that was also observed for the

southern distributions of the species (Lopez

Cazorla 2005), and other species of the genus in

other oceans (MacNair et al. 2001; Yoneda et al.

2007). The larger size attained by females

increases fecundity, while the earlier onset of

maturity of males at a smaller size diverts energy

from growth to reproduction and affects both the

maximum size and longevity (Saborido-Rey and

Kjesbu 2005).

Maximum ages recorded in otoliths in this

study corresponded to eight years in males and

eleven years in females, while the observed age in

scales by Lopez Cazorla (2005) were six years in

males and seven years in females. The correspon-

dence between age readings of both apposition

structures can be considered acceptable; however,

age determination on scales can be less reliable

for older fish because of the crowding of the rings

at the scale border, as is the case of P. dentatus in

the northwestern Atlantic (Sipe and Chittenden

2001) and Pagus pagrus in southern Brazil

(Haimovici et al. 2020). Therefore, it is not

unlikely that further studies of the growth of P.

orbignyanus in Argentina, aged through their

otoliths, produce larger annuli counts than those

observed by Lopez Cazorla (2005).

The total length at which P. orbignyanus

attains sexual maturity in southern Brazil has not

been established with precision, but histological

studies showed that sperm was present in testes of

males under 300 mm and maturing oocytes in

females larger than 385 m (Silveira et al. 1995).

On our growth curves, these lengths correspond

to ages under two for males and three for females.

Fast growth and early onset of maturation are life

history traits associated with increased natural

mortality and shorter lifespans (Adams 1980).

Although less abundant than other Par-

alichthys species in the region, the high price and

large size of P. orbignyanus makes it a valuable

resource for small-scale fishers. The drastic

decrease in recorded landings in the 2000s

(CEPERG 2012) suggests overfishing in southern

Brazil. Avoiding the catch of juveniles in their

shallow estuarine waters and in their nursery

grounds may result in relatively fast stock recov-

ery and, consequently, the potential yield (Hor-

wood et al. 1998). In addition, studies of the

impact of illegal shrimp trawling in the estuary

and beach nets along the coast are required, as

large females are frequently found in shallow

estuarine and coastal waters. Because of differ-

ences in growth between males and females,

intense fishing exploitation can produce changes

in the sex ratio that can negatively affect repro-

ductive success by reducing the probability of

encountering potential mates or by reducing fer-

tilization success (Rowe and Hutchings 2003).

Therefore, the management of this species has to

take into account also the marked difference in

growth between sexes.

HAIMOVICI ET AL.: AGE AND GROWTH OF PARALICHTHYS ORBIGNYANUS

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