Occurrence of Echinorhynchus clavula (Dujardin, 1845) nec Hamann, 1892 (Acanthocephala) in the Fish of Llyn Tegid (Bala Lake), Merionethshire

Abstract

The grayling Thymallus thymallus, pike Esox lucius, roach Rutilus rutilus, and eel Anguilla anguilla of Llyn Tegid were examined for the occurrence of Echinorhynchus clavula; the total infection of these species of fish was 46.0%, 11.5%, 16.1%, and 27.7%, respectively. The degree of infection may be correlated with the feeding of the fish on Asellus meridianus, the only known intermediate host of E. clavula in Llyn Tegid, although in the case of the pike of the size range examined, a secondary establishment of the worms is postulated. The percentage occurrence of male E. clavula was lower than that of female worms. The production of shelled acanthors by female worms may be correlated with the degree of concentration of E. clavula in the fish intestine; thus, in the eel, where maximum concentration was found, maximum production of shelled acanthors was also found. No seasonal periodicity of occurrence and maturation of E. clavula was observed, shelled acanthors were seen during all months except February and December, and the failure to find worms with shelled acanthors in these months is believed to be a sampling deficiency. The literature relevant to the distribution of E. clavula and to the seasonal periodicity of occurrence and development of Acanthocephala is reviewed. It is postulated that temperature may play a significant role in the seasonal periodicity of some Acanthocephala of fishes. Llyn Tegid is a mesotrophic lake, 6 km in length by 1 km in width, situated about 45 km inland from Barmouth on the west coast of Wales. It is the largest Welsh lake and contains 13 species of fish (Chubb, 1963). This paper gives an account of the occurrence of Echinorhynchus clavula (Dujardin, 1845) nec Hamann, 1892 in grayling Thymallus thymallus (L.), pike Esox lucius L., roach Rutilus rutilus (L.), and eels Anguilla anguilla (L.). MATERIALS AND METHODS The fish (Table I) were captured by gill net, seine, or electric fishing. As soon as possible the alimentary tract of the fish was removed, slit longitudinally, and carefully searched. Acanthocephala found were placed in cold water until the proboscis was fully expanded. Fixation was by an alcoholformol-acetic medium as recommended by Van Cleave (1953). Various techniques were tried in order to obtain whole, stained, and cleared Acanthocephala. It was soon discovered that the use of an alcohol series for dehydration was unsatisfactory. Subsequently glacial acetic acid was used for dehydration (Chubb, 1962) and creosote for clearing. At first stains were used, but later were Received for publication 10 May 1963. 52 found to be unnecessary. The procedure finally adopted was as follows: fixation in AFA; dehydration via glacial acetic acid; clearing and preservation in creosote. Mounting in Canada balsam was unsatisfactory, as the fine detail of the unstained worms became invisible owing to excessive clearing. All specimens of E. clavula found were examined. The unstained material was found to be best for assessment of sex and stage of development of the female worms. The females were divided into two groups: one included those worms in which the phases of development of ovarian balls were present, but in which no shelled acanthors had been formed, while the other included worms in which shelled acanthors were observed.