INTRODUCTION

Argentine seabass or “mero” Acanthistius pa-

tachonicus (Jenyns, 1842) is a benthic-demersal

fish that inhabits both soft and hard bottoms at

depths not exceeding 100 m. Distribution of this

species ranges from 30° S (Brazil) to 48° S

(Patagonia, Argentina) in the Southwestern

Atlantic (SWA) (Cousseau and Perrotta 1998).

Argentine seabass comprises an important prey

for top predators such as the South American sea

lion (Otaria flavescens), cooper shark (Car-

charhinus brachyurus), tope shark (Galeorhinus

galeus) and grey nurse shark (Carcharias taurus)

(Koen Alonso et al. 2000; Lucifora 2003; Lucifo-

ra et al. 2006).

It is important to determine the role that each

species plays within the ecosystem and its posi-

tion in the trophic network for a better under-

standing of predator-prey interactions (Pauly et

al. 1998b). Interactions between species affect the

dynamics of marine fish populations (Alonso et

al. 2003), while community structures are strong-

ly influenced by piscivorous predators (Lyons

and Magnuson 1987; Tonn et al. 1992; Scharf et

al. 1997). On the other hand, studies in trophic

MARINE AND FISHERY SCIENCES 33 (1): 69-75 (2020). https://doi.org/10.47193/mafis.3312020061804

BACK-CALCULATION OF TOTAL LENGTH OF ARGENTINE SEABASS

Acanthistius patachonicus USING MORPHOMETRIC RELATIONSHIPS OF BONES

AND MEASUREMENTS OF THE BODY

CECILIA M. RIESTRA1, JORGE E. PEREZ COMESAÑA2, 3, †, KARINA A. ARIAS3,

LEANDRO L. TAMINI3and GUSTAVO E. CHIARAMONTE2, 3

1Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP),

Paseo Victoria Ocampo Nº 1, Escollera Norte, B7602HSA - Mar del Plata, Argentina

e-mail: cmriestra@inidep.edu.ar

2División Ictiología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”,

Av. Ángel Gallardo 470, C1405 - Ciudad Autónoma de Buenos Aires, Argentina

3Estación Hidrobiológica de Puerto Quequén,

Av. Almirante Brown y Calle 520 s/n, B7631 - Quequén, Argentina

ABSTRACT. Predictive regression equations were generated to estimate total length of the Argentine seabass

(Acanthistius patachonicus) using skull and pectoral girdle bones, specific body, and otolith lengths. Regressions of

skull and pectoral girdle bones, specific body and otolith lengths were all statistically significant. Generating regres-

sions between specific bones and external characteristics of the body meaningfully increases the ability to analyse the

information obtained from studies of stomach contents of predator fish from the Southwestern Atlantic Ocean.

Key words: Diagnostic bones, piscivores, top predators, diet.

†Deceased 16 September 2015.

ecology have become relevant in recent years

because of their use in the construction of indices

for evaluating the health of ecosystems (Pauly et

al. 1998a, 1998b). Regarding these indices, the

trophic level has been extensively used to evalu-

ate the state of fisheries, as well as to determine

the existence of over-exploitation and the sustain-

ability of these fisheries over time (Pauly et al.

1998a, 2001, 2002). Therefore, it is extremely

important to accurately achieve great precision in

the evaluation of the diet of any predator, includ-

ing size and weight of the ingested prey, informa-

tion that is essential to define future management

and conservation strategies (Cherel et al. 2000).

Because of the difficulty of directly assessing a

predator's diet by field observations, feeding stud-

ies are based on the examination of stomach con-

tents that have not been fully digested. Usually, the

identification of prey species, as well as the esti-

mation of their length and weight, has been based

on the analysis of otoliths. The otolith is a calcified

structure that is differentially digested in the stom-

ach of predators, completely dissolved (North et

al. 1984; Jobling and Breiby 1986) or significantly

eroded modifying their morphology and making

measurements and taxonomic identification more

complex (Johnstone et al. 1990). Thereby, the

presence of certain species could be underestimat-

ed or ignored, leading to biased estimates of the

original prey sizes and the amount of prey con-

sumed (Jobling and Breiby 1986). Diagnostic

bones concerning the body length allow estimat-

ing both the ingested biomass as the prey age class

in the study of the diet of piscivorous predators

(Gosztonyi et al. 2007). Nowadays, skull and

shoulder girdle bones are a complement of the use

of otoliths in diet studies because of its resistance

to digestion (Hansel et al. 1988; Scharf et al. 1997,

1998; Gosztonyi et al. 2007; González Zeballos et

al. 2010; Perez Comesaña et al. 2013, 2014).

This paper presents the linear regression and

predictive total length equations for A. patachon-

icus based of the length of the cranial bones,

scapular bones, otoliths and specific body meas-

urements. These equations constitute a comple-

mentary tool to optimize the quantitative studies

of the diet of marine piscivorous predators.

MATERIALS AND METHODS

Two hundred specimens of A. patachonicus

captured by commercial bottom trawl vessels

operating at Puerto Quequén, Buenos Aires

Province, Argentina (fishing area: 38° 40′ S-39°

50′ S, 57° 68′-60° 08′ W) during 2013, were

analysed. Total length, predorsal length, preanal

length and head length in centimetres (±1 mm)

were registered (Figure 1) and immediately

frozen. Diagnostic bones were selected according

to Gosztonyi and Kuba (1996). Fish were placed

in boiling water for a period no longer than 2 min,

depending on the size of the specimen, to remove

bones. Once separated from the soft tissues,

bones were measured using a calliper (±0.05

mm) (Figure 2). Least square regression equa-

tions were generated using INFOSTAT/L (Di

Rienzo et al. 2010) to predict original total length

of A. patachonicus based on the predorsal, pre-

anal and head lengths. In addition, skull bones

measurements such as hyoid bar length, clei-

thrum length, dentary length, maxilla length, pre-

maxilla length, opercle length, preopercle length,

vomer length, hyomandibula length, parasphe-

noids length and otolith length have been used

(Figure 2). Total lengths were regressed on meas-

urements of the remaining bones.

RESULTS

Total length of Argentine seabass ranged

between 207 and 584 mm. Regressions relating

body measurements to total length were highly

signiﬁcant (p < 0.0001). The coefficient of deter-

mination (r2) related to body measurements took

70 MARINE AND FISHERY SCIENCES 33 (1): 69-75 (2020)

values between 0.88 and 0.96, being the preanal

length the one that showed a better fit (Table 1).

Also, values of the coefficient of determination

for the lengths of diagnostic bones varied

between 0.90 and 0.96. The best fit was obtained

with the preopercle (measure 2, Figure 2) (r2=

0.96), slightly higher than those obtained with the

opercle, hyoid bar, dentary (measure 1, Figure 2),

all of them with r2=0.95, and the cleithrum (r2=

0.94), as well as the otolith length also showed a

good fit (r2=0.91) (Table 1).

All measurements, whether from diagnostic

bones or from body lengths or otoliths, showed

significant relationship with total length. Regres-

sions obtained from diagnostic bones, especially

preopercle (measure 2), dentary (measure 1),

opercle, hyoid bar and cleithrum appear to be reli-

able predictors of the length of A. patachonicus.

DISCUSSION

It is well known that the external morphology

of a prey fish can be distorted by the effect of the

predator’s digestive process, which can lead to

biased measurements. If prey was consumed

recently, external morphological measurements

can be estimated in an accurate way, becoming an

appropriate alternative to that of the diagnostic

bones, as is the case of the preanal length in the

present work. However, back-calculation of the

original dimensions of a fish from measurements

of diagnostic bones is not as susceptible to error

as that taken from external body measurements

(Perez Comesaña et al. 2013).

It must also be recognized that reconstruction

of the original size of fish prey from diagnostic

bones has some limitations. The effect of preserv-

atives on bone size should be taken into consider-

ation if stomach contents are stored in a chemical

stabilizer (Hansel et al. 1988; Scharf et al. 1997).

Another potential problem is the use of boiling

water to facilitate the separation of soft tissue

bones. It can cause deformation and contraction of

bones if an excessive time elapses between boil-

ing and taking of measurements. These drawbacks

were avoided in the present work since individu-

als were frozen, then thawed and boiled at con-

trolled time intervals and subsequently measured

after extraction and separation of bones.

In recent studies of the early development of A.

patachonicus, preopercle complex has been

pointed out as the most important characteristic

RIESTRA ET AL.: BACK-CALCULATION OF THE TOTAL LENGTH OF ACANTHISTIUS PATACHONICUS

Figure 1. Body length measurements of Acanthistius patachonicus. 1: length of the head, 2: predorsal length, 3: preanal length,

4: total length.

72 MARINE AND FISHERY SCIENCES 33 (1): 69-75 (2020)

Figure 2. Bones and otolith measurements. A: maxilla, B: premaxilla, C: dentary, D: vomer, E: parasphenoids, F: angular, G: clei-

thrum, H: hyomandibula, I: otoliths, J: hyoid bar, K: opercle, L: preopercle. Numbers (1) and (2): registered measure-

ments.

1 cm

that allowed the reconstruction of the develop-

ment from larva to adult stage (Villanueva Gomi-

la et al. 2015). Our results showed that two bones

from the preopercle complex (preopercle and

opercle) are also important as predictors of total

length of A. patachonicus. Likewise, our results

showed as well that dentary, hyoid and cleithrum

bar bones, aside from the distance to the anterior

insertion of the anal fin, are also good predictors

of total length of A. patachonicus.

We have found that all measurements of the

cranial bones of A. patachonicus showed a signif-

icant relationship with total length and that

regressions obtained from diagnostic bones were

reliable predictors of length. Thereby, regression

equations calculated from cranial bones and

external body measurements presented in this

work increased the quali-quantitative potential of

the information obtained from the analysis of

stomach contents of piscivorous predators of the

Southwestern Atlantic Ocean.

ACKNOWLEDGEMENTS

To Gustavo Carrizo for the drawings of the fig-

ures. Juan and Roque Bruno from the Santa

Cecilia fish market. To José Ricci for share their

facilities. To the reviewers for the constructive

comments on earlier draft of the manuscript.

INIDEP contribution no 2163.

RIESTRA ET AL.: BACK-CALCULATION OF THE TOTAL LENGTH OF ACANTHISTIUS PATACHONICUS

Table 1. Estimated parameters of predictive regression equations of data versus total length Acanthistius patachonicus (y =a +

bx). x: variable in mm, y: total length in mm, n: sample size, r2: coefficient of determination, SE: standard error, CI: con-

fidence interval. Numbers (1) and (2): measurements illustrated in Figure 2.

Variables (mm) n r2 a ±SE (CI 95%) b ±SE (CI 95%)

a. Maxilla (1) 200 0.93 -6.03 ±6.71 (-19.26 – 7.20) 8.18 ±0.15 (7.87 – 8.48)

b. Premaxilla (1) 193 0.92 -12.04 ±7.80 (-27.42 – -3.34) 49.84 ±1.08 (47.71 – 51.97)

(2) 199 0.93 -10.19 ±6.80 (-23.61 – 3.23) 11.98 ±0.23 (11.53 – 12.43)

c. Dentary (1) 197 0.95 -8.46 ±5.93 (-20.15 – 3.23) 16.78 ±0.28 (16.23 – 17.33)

(2) 196 0.90 26.81 ±7.50 (12.02 – 41.60) 16.78 ±0.28 (16.23 – 17.33)

d. Vomer (1) 193 0.93 11.05 ±6.96 (-2.68 – 24.77) 36.82 ±0.76 (35.33 – 38.42)

(2) 191 0.91 -9.28 ±8.27 (-25.59 – 7.03) 15.48 ±0.36 (14.78 – 16.19)

e. Parasphenoid (1) 191 0.92 -30.00 ±8.22 (-46.22 – -13.79) 6.21 ±0.14 (5.94 – 6.48)

f. Angular (1) 197 0.91 -1.10 ±7.82 (-16.53 – 14.33) 9.34 ±0.21 (8.93 – 9.75)

g. Cleithrum (1) 180 0.94 -7.82 ±7.00 (-21.63 – 5.99) 5.18 ±0.10 (4.98 – 5.38)

h. Hyomandibula (1) 197 0.93 0.75 ±6.95 (-12.97 – 14.46) 16.62 ±0.33 (15.97 – 17.28)

(2) 187 0.93 -6.12 ±6.77 (-19.47 – 7.24) 12.10 ±0.23 (11.64 – 12.55)

i. Otolith (1) 197 0.91 -114.94 ±10.58 (-135.82 – -94.07) 31.30 ±0.72 (29.89 – 32.72)

j. Hyoid bar (1) 196 0.95 -19.32 ±6.04 (-31.24 – -7.40) 12.98 ±0.21 (12.56 – 13.04)

k. Opercle (1) 198 0.95 12.77 ±5.71 (1.50 – 24.04) 11.07 ±0.19 (10.70 – 11.44)

l. Preopercle (1) 198 0.90 -17.44 ±8.81 (-34.82 – -0.06) 19.75 ±0.48 (18.81 – 20.69)

(2) 198 0.96 -17.63 ±5.01 (-27.51 – -7.75) 7.56 ±0.10 (7.35 – 7.76)

Head length 185 0.89 11.55 ±8.60 (-5.42 – 28.52) 2.96 ±0.08 (2.81 – 3.12)

Predorsal length 183 0.88 53.66 ± 8.13 (37.61 – 69.71) 2.95 ±0.08 (2.79 – 3.11)

Preanal length 185 0.96 24.58 ±4.84 (15.03 – 34.13) 1.65 ±0.02 (1.60 – 1.70)

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Received: 9 January 2020

Accepted: 1 May 2020

RIESTRA ET AL.: BACK-CALCULATION OF THE TOTAL LENGTH OF ACANTHISTIUS PATACHONICUS