Development and habitat selection of a new sanguinicolid parasite of cultured greater amberjack, Seriola dumerili, in the Mediterranean

摘要

This study presents a description of the developmental stages of a new sanguinicolid disease agent (Paradeontacylix ibericus) of cultured Seriola dumerili (greater amberjack) in the Mediterranean, and investigates parasite habitat selection in the definitive host and the development of sanguinicolidosis in experimental, inshore cultures of S. dumerili. Two experimental surveys were carried out using fish captured as wild 0+ juveniles in the aquaculture facilities at Puerto de Mazarrcdn (Spain). Encysted, early post-cercarial stages (schistosomula) were detected in histological sections of the pelvic and thoracic muscles of fish and four subsequent stages of parasite development were distinguished and described based on the size and the degree of development of the reproductive system of the flukes. In contrast to freshwater sanguinicolids P. ibericus exhibits a developmental pattern characterised by a prolonged maturation, long life span, and simultaneous occurrence of both the juvenile and adult parasite stages. Although flukes were recovered from four sites in the host the thoracic and pelvic girdle muscles, where the blood flukes were found initially, were the main habitat for P. ibericus. The worm intensity per habitat gradually decreased in those sites in the blood system located furthest from the girdles. This habitat selection pattern was not density-dependent. The developmental pattern of sanguinicolidosis due to P. ibericus is compared with previous studies on sea-cage cultured S. dumerili. The lack of severe pathology observed in the present study is attributed to the low pathogenicity of the parasite and the aquaculture conditions. The results of this study could be useful for early diagnosis of P. ibericus before transfer of the fish to aquaculture facilities and to design control measures for cultivating S. dumerili.