Studies on the biosystematics of Trichodinid ciliates parasitic on British freshwater fish.

Abstract

Of the numerous reports of trichodinids from British freshwater fish only four have been to species level, representing three Trichodina species and one Trichodinella species. Twenty freshwater fish species were sampled from approximately sixty sites in Scotland, England and Wales. Skin and gill smears were prepared using Klein’s silver staining technique, and morphometric measurements made from features of the adhesive di.sc taken from enlarged photomicrographs according to Lorn’s (1958) taxonomic criteria. The adoral cilia, used as a feature of generic classification were described for each trichodinid population from live preparations. Species discrimination and investigation of mtraspecific morphological variation was aided by the u.se of Principal Components and Cluster analysis. Thirteen trichodinid species were identified from British freshwater fish during this study including: Trichodina acuta Lorn, 1961 from Cyprinus carpio, Carassius auratus, Oncorhynchus mykiss, and Phoxinus phoxinus; Trichodina domerguei Wallengren, 1897 from Gasterosteus aculeatus; Trichodina tenuidens Faure-Fremiet, 1944 from Gasterosteus aculeatus; Trichodina pediculus Ehrenberg, 1838 from Gasterosteus aculeatus; Trichodina modesta Lorn, 1970 from Ahramis hrama; Irichodina nif>ra Lorn, I960 from Cyprinus carpio, Salmo trutta and Oncorhynchus mykiss; Trichodina mutahilis Kazubski & Migala, 1968 from Phoxinus phoxinus; Trichodina rostrata Kulemina, 1968 from Phoxinus phoxinus; Trichodina intermedia Lorn, I960 from Phoxinus phoxinus; Trichodinella epizootica Raabe, 1950 from Perea fluviatilis and Oncorhynchus mykiss; Tripartiella lata Lorn, 1963 from Phoxinus phoxinus; Tripartiella copiosa Lorn, 1959 from Phoxinus phoxinus and Paratrichodina incisa Lorn, 1959 from Phoxinus phoxinus. Ahramis brama and Rutilas rutilas. Many of the previous species demonstrated considerable inter and intrapopulational morphological variation. Immature specimens of Trichodina acuta, Trichodina domerguei, Trichodina tenuidens and Trichodina intermedia were examined, elucidating developmental morphology and its taxonomic relevance. A .study of intraspecific morphological variation was undertaken by sampling trichodinids from a population of Gasterosteus aculeatus over a twelve month period. Regression analysis indicated statistically significant negative correlations between water temperature and measurements of the adhesive disc in Trichodina domerfpiei and Trichodina tenuidens. Principal Components Analysis was utilised to differentiate extreme morphological variants of the two previous species. A sonication technique modified from Shinn et al. (1993) was used to i.solate skeletal structures of the adhesive disc from Trichodina domerf^uei, Trichodina intermedia, Paratrichodina incisa and Trichodinella epizoótica for .scanning electron micro.scopy. New structures which were previously undescribed are discussed, including denticle apophyses, denticular pins and a small peg-like structure on the central parts ot the denticles. Actual denticle structure is compared to that visualised by silver staining using light microscopy, and its implications for generic classification of the trichodinids is commented upon.