Iris Publishers- Journal of Oceanography and Marine Biology| Morphological Abnormalities in Rajidae Species (Chondrichthyes) From the Gulf of Gabès (Tunisia, Central Mediterranean Sea): What Causes?

Authored by Sondes Marouani

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.

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).

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