Identification of Hysterothylacium (Nematoda: Raphidascarididae) larval morphotypes infecting marine fish caught off the aegean coast of Turkey

To date, larvae of Hysterothylacium aduncum, H. fabri, and H. reliquens have been reported in some marine fish caught along the coasts of Turkey's Aegean Sea. However, the presence of Hysterothylacium larval morphotypes in fish caught in the Aegean Sea has not been investigated. In this thesis, it is aimed to reveal the morphological identification of Hysterothylacium larval morphotypes and molecular characterization of rDNA ITS gene regions in different species of marine fish caught in the Aegean Sea. A total of 16 different marine fish species including Belone belone (garfish), Boops boops (bogue), Engraulis encrasicolus (European anchovy), Euthynnus alletteratus (little tunny), Lithognathus mormyrus (sand steenbras), Mugil spp. (mullet), Mullus barbatus (red mullet), Mullus surmuletus (surmullet), Sardina pilchardus (European pilchard), Sarpa salpa (salema), Saurida undosquamis (brushtooth lizardfish), Scorpaena spp. (scorpionfish), Spicara maena (blotched picarel), Trachurus mediterraneus (Mediterranean horse mackerel), Trigla lyra (Piper gurnard), and Upeneus moluccensis (Indo-Pacific threadfin bream) caught in the Aegean Sea were examined. Nematodes were collected one by one and Hysterothylacium sp larval morphotypes were identified after morphological examinations. The rDNA ITS gene of randomly selected samples from larval morphotypes was amplified and subsequently sequenced. Herein, Hysterothylacium sp. larval morphotypes IV, V and VIII were morphologically identified from the Aegean Sea. Phylogenetic relationships were determined by revealing the nucleotide structures of the rDNA ITS gene regions of these morphotypes. Hysterothylacium sp. larval type V was detected for the first time in Spicara maena (blotched picarel) fish species caught in the Aegean Sea. Therefore, S. maena is a new host for the fish species Hysterothylacium sp. larval type V. Moreover, the ITS gene sequence of the type V morphotype detected in Turkish territorial waters was obtained for the first time. The ITS sequences of morphotypes IV, V, and VIII identified here provide valid genetic data for the identification of larval morphotypes capable of infecting different fish species.