Open Access Research Article

Morphological Abnormalities in Rajidae Species (Chondrichthyes) From the Gulf of Gabès (Tunisia, Central Mediterranean Sea): What Causes?

Sondes Marouani*, Fekher Ben Jarray, Sami Karaa and Othman Jarboui

National Institute of Sciences and Technologies of the Sea (center of Sfax), Tunisia

Corresponding Author

Received Date: December 19, 2018;  Published Date: January 04, 2019

Abstract

This study reports the occurrence of morphological abnormalities in four Rajidae specimens caught by a commercial trawler in the Gulf of Gabès (Tunisia, Central Mediterranean Sea): absence of tail and asymmetric pectoral fins in a female of the thornback ray Raja clavata Linnaeus, 1758 and absence of the caudal and dorsal fins in two female Raja clavata specimens and in one female Raja radula Delaroche, 1809 specimen. These cases of abnormality were described, commented and discussed.

Keywords: Raja clavate; Raja radula; Morphological abnormalities; Rajidae; Gulf of gabès; Central mediterranean sea

Introduction

The family Rajidae is the most diverse group of batoids, with 27 genera and about 245 species distributed worldwide [1].

The thornback ray Raja clavata Linnaeus, 1758, is a shallow water demersal skate found in the eastern Atlantic from Norway to South Africa, including the Mediterranean and Black Seas [2]. This species is widespread in the Mediterranean Sea and is the dominant skate in commercial landings [3]. The thornback ray occurs along the Tunisian coasts mainly in the Gulf of Gabès where it is caught throughout the year by commercial trawl fisheries as by catch [4].

The rough ray Raja radula Delaroche, 1809 is a relatively small skate endemic to the Mediterranean Sea [5]. The species abound along Tunisian coasts mainly in the Gulf of Gabès where it is taken as a by-catch by trawlers, demersal gill-nets and longlines and usually captures are marketed [6].

Morphological abnormalities have been reported in batoids, such as: conditions spinal and fin deformities in the axial skeleton [7], bicephalia [8], albinism [9], hermaphrodism [10] and the incomplete formation of some body parts [11-14], Morphological abnormalities were listed also in sharks [15-17]. The most common abnormalities in skates (Order Rajiformes) and rays (Order Myliobatiformes) is where the pectoral fins are not fused to the head. This type of abnormality had been recorded by different authors [14,18-23] for several species of Rajidae (Raja brachyuran, R. asterias, R. clavata, R. radula, R. radiata, R. miraletus, R. castelnaui, A. cyclophor, A. platana), Torpedinidae (Torpedo marmorata), Rhinobatidae (Rhynchobatus djiddensis), Gymnuridae (Gymnura poecilura), Potamotrygonidae (Potamotrygon motoro), Dasyatidae (Dasyatis longa, D. dipterura, D. akajei, Himantura uarnak, Pteroplatytrygon violacea).

Investigations conducted from early 2016 to date in the southern Tunisian waters to study the impact of deep-sea fishing on the resources and the benthic ecosystems of the Gulf of Gabès using an observer on board, allowed the capture of three female Raja clavata and one female R. radula malformed. These specimens were described in the present paper, with comments and discussion on morphological abnormalities reported in batoid species.

Material and Methods

The malformed specimens were caught by the commercial trawler “Baati” using a 24mm stretched mesh size cod-end and operates in the Gulf of Gabès. The three malformed specimens of Raja clavata was caught at depth of 47 and at 50m, whereas the malformed R. radula was caught at depth of 47m (Figure 1).

Those specimens were identified according to Ebert and Compagno (2007) [1]. The total mass (TM) was weighted to the nearest 10g. Morphometric measurements were recorded to the nearest centimeter followed [24]. Photographs of the specimens were available.

Results

The three thornback ray specimens were females with a DW of 54.4cm (Figure1), 34.8cm (Figure 2) and 25.3 cm (Figure 3). respectively, and weighted 2130g, 1834g and 642.45g. respectively. The female rough ray was 36cm (Figure 4) in disk width and 1920.7g in total mass.

The morphometric measurements of the specimens were shown in the (Table 1). The abnormality in specimens was focused in the posterior portion of the body. The R. clavata specimen (Figure 1) presented a morphological abnormality at tail which is absent as well as at the pectoral fins which were asymmetric (Figure2). Whereas the caudal and dorsal fins were lacking in R. clavata specimens (Figures 2&3) and in the R. radula specimen (Figure 4).

Table 1:

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irispublishers-openaccess-oceanography-marine-biology
irispublishers-openaccess-oceanography-marine-biology
irispublishers-openaccess-oceanography-marine-biology
irispublishers-openaccess-oceanography-marine-biology

Discussion

The present report contributes with information about the presence of an abnormality in females of R. clavata and R. radula. This morphological abnormality is not due to an injury as it is generally the case in skates [25]. No scar was visible and all the posterior part was covered by pigmented skin.

Ribeiro-Prado, et al. [10] listed all morphological abnormalities recorded to date in skates and rays, and noted that abnormalities occurred in disc, with pectoral fins non-adherent to the head being the most recorded one. The later not only concerned skates but also rays and rarely torpedinids. A case of abnormality in R. radula was reported by Capapé C, et al. [26]. Another case of morphological abnormality in tail was observed in a common torpedo T. torpedo in Tunisian waters, the specimen exhibiting a surnumerary dorsal fin [27]. Recently, Capapé C, et al. [28] noted tail abnormality in three specimens of Raja clavata captured off the Syrian coast; a juvenile male with an ecaudated tail reduced to a stump like structure and two other female and male adults without dorsal and caudal fins.

Based on the reported median disc width at maturity for the thornback ray and the rough ray [29], those animals were mature and captured alive. Therefore, we assume the adaption of the specimens for the anomaly and that these abnormalities in tail and asymmetric fins did not prevent the individual from obtaining good food supplies and it appears that these abnormalities did not affect the development of the specimen and it reached similar parameters and swimming activities than the normal ones.

Congenital abnormalities are usually linked to different causes as: endogamy [30], parasites [31] or with exposure to environmental degradation or pollution of the mother [32].

The malformation reported here seems to be derived from the failure of the anterior lobes of the pectorals fins to join with the head during embryonic development [11] however the cause (or causes) of this condition remains unknown.

Unfortunately, this study cannot be conclusive about the causes of this specifically malformation and further studies should be done on this and other species to identify their possible causes.

Acknowledgement

The authors are especially grateful to all the staff of the trawler “Baati”, with whom works the observer on board, for their help and assistance.

Conflict of Interest

No conflict of interest.

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