Life cycle and seasonal dynamics of Cucullanus cirratus O.F. Muller, 1777 (Nematoda, Ascaridida, Seuratoidea, Cucullanidae) in Atlantic cod, Gadus morhua L.

摘要

Mature specimens of Cucullanus cirratus were obtained from the pyloric caeca and intestines of Atlantic cod, Gadus morhua, from Danish waters, in order to study the life cycle of this species. Eggs laid by mature females hatched after 1-4 weeks (depending on temperature) to release 3rd-stage larvae about 400μm long, with amphids and dereids. These were infective to calanoid and cyclopoid copepods and sand gobies, Pomatoschistus minutus. They entered the haemocoel of copepods but did not grow. In gobies, they entered the intestinal mucosa and grew to 800μm in length within 6 months. They were not encapsulated. Experimental infections of cod (8-30 cm long) showed that free-living 3rd-stage larvae were not infective, whereas those >700μm long, obtained from gobies, survived in the cod. Third-stage larvae 700-1200μm long occurred in the stomach mucosa, where they developed and moulted to 4th-stage larvae, which then migrated to the pyloric caeca and anterior part of the intestine, where they moulted and developed to the mature adult stage. No developmental stage became encapsulated. No invertebrates and only one of 40 P. minutus were naturally infected. Naturally infected cod (>20 cm total length) harboured moulting third-stage larvae and <2 mmlong fourth-stage larvae 2 months post capture. Naturally infected 4- to 5-month-old codlings (8-10 cm total length) harboured 2-3 mm long fourth-stage larvae only, indicating that they had acquired the third-stage larvae as planktivorous fry only a fewcentimetres long. It is suggested that C. cirratus may have a life-cycle that involves copepod transport hosts and fish intermediate hosts (gobies or cod fry). Examinations of 350 naturally infected cod (8-78 cm long) showed that group 1 and older cod contained 3rd-stage larvae, intermediate stages and adult worms, indicating that they could become infected throughout the year; however the pattern of infection suggested that cod over 20 cm long became infected mainly in summer by eating infected fish (including smaller cod). The maximum prevalence of third-stage larvae occurred in spring and summer. The greatest prevalence of gravid worms was observed in autumn.