Diclidophora merlangi (Monogenea: Diclidophoridae) on Atlantic cod, Gadus morhua

Diclidophora merlangi (Kuhn, in Nordmann, 1832), as species specific to whiting, Merlangius merlangus (Linnaeus, 1758), is reported and described for the first time on the gills of Atlantic cod Gadus morhua (Linnaeus, 1758). Of the about 1,200 cod examined in this article, only 2 specimens of D. merlangi occurred on 2 fish, suggesting that they represented accidental infections. The 2 specimens showed specific traits of D. merlangi, but their size was considerably smaller than that of D. merlangi on whiting. Principal-component analyses showed that the morphology of the specimens on cod was more similar to that of D. merlangi than those of other congeneric species from the North Atlantic, additionally supporting their assignment to D. merlangi. Quantitative data documenting the potential reproductive consequences of D. merlangi occurring on cod is also provided. The testes and germaria of the specimens on cod were noticeably smaller than those of D. merlangi on whiting, but the number of testes was similar and spermatozoa were observed in the sperm duct. By contrast, the aspect and smaller size of the oocytes suggested that D. merlangi on cod could not produce viable ova, although 1 specimen exhibited an egg with normal sized and shaped capsule.

Marine parasites as pollution indicators: an update

Eight major reviews are cited to indicate a recent knowledge explosion on the use of marine parasites as potential indicators of pollution. A literature update is given for the period 1995–2001. An analysis of the publications cited is used to provide 10 refined criteria for selecting parasites as indicator/monitor species. Previously unpublished data on Diclidophora merlangi and Dictyocotyle coeliaca confirm their value as potential indicators of hydrocarbon pollution in the North Sea. An extensive knowledge of D. merlangi is summarised to emphasize its potential value as an indicator species and also to encourage studies on the health status and immune responses of its host when subjected to pollutant stressors and infection with this monogenean. A discussion focuses on publications which have reported significant recent advances in this area of research and also on accompanying issues, problems and controversies. These selected publications are used to suggest species, stages in the development of species and assemblages of species worthy of further more detailed investigations into their value as indicators/monitors of pollution. It is predicted that further good progress will be made when contaminants can be accurately identified, their precise effects on both host and parasite can be measured by histochemical and biological methods and the roles of contaminants and parasites in causing disease can be assessed separately. About 100 references are cited.

Sexual reproduction in the monogenean Diclidophora merlangi: tissue penetration by sperms

Copulation between pairs of adult Diclidophora merlangi detached from the host was frequently observed. The spined penis of one animal always attaches to a second worm at a latero-ventral position posterior to the genital openings. There is no vagina. The sperms travel between the cells of the recipient to reach the seminal receptacle. The ultrastructure of the sperm is described. Positions of adult D. merlangi on the gills of the host would facilitate pairing for sperm transfer.