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Bull. Eur. Ass. Fish Pathol., 27(6) 2007, 2S0

Occurrence of Benedenia sciaenae van Beneden, 1856 (Monogenea: Capsalidae) in cultured

meagre (Argyrosomus regius Asso, 1801) (Teleost: Sciaenidae) from western Turkey

E. Toksen1*, K. Buchmann2 and J. BrescianF

1 Department of Aquaculture, Faculty of Fisheries, Ege University, Bornova, 35100, Izmir, Turkey;

2Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.

Abstract

An investigation was conducted on the causes of scale loss and severe local lesions on the skin of cultured meagre (Argyrosomus regius Asso, 1801) reared in net cages in the Mediterranean along the Turkish host. This species is an important alternative species to the sea bass and sea bream in Turkish mariculture. All of the 40 fish examined (mean body weight S.63 kg SD 0.89 kg, mean body length 91.3 cm SD 3.6 cm) showed numerous monogenean parasites on the area with lesions. The parasite was identified as Benedenia sciaenae van Beneden, 18S6 (Monogenea : Capsalidae). The prevalence was 100 % and the mean intensity 227 (SD 77.5) parasites per host. Scanning electron micrographs of the causative parasite are presented. This is the first report of B. sciaenae in Turkey.

Introduction

The teleost Argyrosomus regius, which is a

member of the family Sciaenidae is

distributed along the Mediterranean, the Sea

of Marmara, along the west cost of the Black

Sea, the Red Sea and occasionally in the Indian

Ocean (Quemer, 2002). It has been accepted

as an alternative species having a high

potential in aquaculture due to its fast growth,

high feed conversion ratio, survival under a

wide range of salinities and its excellent flesh

quality (Poh et aI., 2001). Thus, growth trials

including this species have been done in Italy,

France and Turkey (Stipa & Angelini, 200S).

The first commercial production was

established in Turkey during 200S but farmers

reported occurrence of scale losses and skin

lesions already during the first season.

* Corresponding authors E-mail: erol.toksen@ege.edu.tr

Therefore the present investigation was

conducted in order to elucidate possible

causes. We hereby report on the occurrence

of B. sciaenae associated with the lesions and

discuss the possible parasitic impacts on

meagre.

Materials and methods

This study was carried out using fish collected

in a net cage located along the coast near

Akbiik (western part of Turkey) inApri1200S.

Forty specimens of Argyrosomus regius were

sampled. The fish were anesthetized with

phenoxyethanol and the total weight and

length of fish were measured. A large number

of parasites were observed with the naked eye

on the skin of the fish. They were collected

with tweezers, counted and investigated

Figure 1. Scanning electron microscopy of Benedenia scianeae, whole worm, ventral view, anterior attachment organs (arrows). Scale bar 1 mm.

under the light microscope. The prevalence,

parasite range and mean intensity (Bush et aI.,

1997) of the parasites were calculated for the

spring season. Some parasites were fixed in

4% neutral formaldehyde, brought to the

laboratory for further investigation and

measurements which were done by the use

of an Olympus BH2 binocular microscope

fitted with a calibrated eyepiece. Formalin

fixed parasites were post-fixed in 2.3% neutral

glutaraldehyde (24h), washed in distilled

water, immersed in 2% tannic acid,

dehydrated, critically point-dried, sputtered

with gold and studied in a FEI Quanta 200

ESEM scanning electron microscope.

Results

Cultured meagre (5.63 ± 0.89 kg in weight, 91.3

± 3.6 cm in length) with hemorrhagic lesions

and scale losses, were observed to rub the

body surface against the net of the cage. While

Bull. Eur. Ass. Fish PathoI., 27(6) 2007, 251

Figure 2. Scanning electron micrograph of opisthaptor (oh) with the marginal extension (black arrows) and protruding accessory sclerites (white arrows) and . Scale bar 500 !lm.

the reasons of these lesions were being

investigated, parasites as big as that can be

seen with the naked eye were found in the

hemorrhagic parts of the skin. The parasites

were identified as Benedenia sciaenae following

the diagnostic keys outlined by Yamaguti

(1963) and Whittington (2001). Measurements

obtained from forty specimens were as follow

(in micrometer) given as range and mean (in

parenthesis): total length of the parasite

including haptor: 10.000-17.000 (14.300)

(Figure 1), maximum breadth: 7.000-9.000

(8.200) at the level of testes. Haptor: 5.680-

6.400 (6.020) x 5.600 - 6.000 (5.800) (Figure 2).

Accessory sclerites: 640-1056 (848) (Figure 2).

Anterior hamuli: 260-325 (290), posterior

hamuli: 221-299 (256) (Figure 3). Moreover,

the opisthaptor had a marginal extension

surrounding the haptor as a skirt (Figure 2).

Anterior attachment organs were 1.360 -1.800

(1.580) x 1.280-1.640 (1.466) appearing more

muscular than glandular (Figure 4). Pharynx

was 1.680 -1.920 (1;800) x 1.520- 1.680 (1.600).

Genital pores were at next to the left anterior

I I

'I I

( j(

Bull. Eur. Ass. Fish Pathol., 27(6) 2007, 252

Figure 3. Posterior hamuli. Scale bar 40 f.1m.

haptor of parasites. Pigmentation was

observed on the dorsal side of the body. All

sampled fish were found to be infected

(prevalence 100 %). Totally, 9.088 monogenean

were counted in 40 infected fish. Parasite

abundance ranged from 84 to 386. Mean

intensity of parasite numbers was 227 (SD

77.5).

Discussion

Meagre has been cultured in aqua culture

farms as an alternative marine fish species in

some Mediterranean countries (Stipa & Angelini, 2005) but only few data are available

on the parasitic diseases of meagre. This

report documents the occurrence of B. scianeae

in cultured meagre in Izmir, Turkey and

suggest that the parasites are responsible for

pathological changes of the host skin. The

mono gene an B. sciaenae was first discovered

Figure 4. Scanning electron micrograph showing anterior part with the two adhesive pads (arrows). Scale bar Imm.

by van Beneden (1852) on the surface of the

European leanfish (Sciaena aquila) (now

Argyrosomus regius) and was followed by later

studies by Goto (1899), Palombi (1949),

Bussey (1986) and Whittington (1996)

reporting the parasite. In the present study,

parasites having a large body size, possession

of separate but closely apposed male and

female pores; and the posterior position of the

large accessory sclerites possessing distinctive

surrounding tissue in the haptor were

observed. These findings and measurements,

which are similar to those of Whittington

(1996), are important to distinguish species

in the genus Benedenia. The authors van

Beneden (1856) and Palombi (1949) reported

dark ruby pigment in the dorsal area. Dark

brown or black pigment aggregations

throughout the body and the haptor of the

parasite were observed in our study which

corresponds to observations by Whittington

(1996). Further, the measurements obtained

in this work clearly correspond to the

description of B. sciaenae done by Whittington

(1996). The scanning electron microscopy

studies revealed the main attachment organs,

opisthaptor, which was equipped with few

externally exposed sclerites and adhesive

pads. These could to some extent probably

inflict some damage to the host epidermis.

However, it is likely that also the feeding

activity itself (due to high parasite burdens

and high energy demand of the worms) may

be more important elements of pathogenesis.

The subsequent rubbing of the body surface

against various structures in the net-pens

(caused by skin irritation) may be responsible

for further skin damages. Generally, the high

prevalence and parasite occurrence associated

with the skin lesions suggest that these

parasites are rather pathogenic and at least

partly responsible for the pathological

changes of the host skin. Therefore the results

call for further studies on development of

sustainable control methods of this parasitosis

in order to secure production and welfare of

cultured meager.

Acknowledgements

The authors are indebted to Dr. 1. Whittington

for confirming the identity of the parasite.

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