ORIGINAL PAPER M. Oumouna Æ S.L. Hallett Æ R.W. Hoffmann M. El-Matbouli Seasonal occurrence of actinosporeans (Myxozoa) and oligochaetes (Annelida) at a trout hatchery in Bavaria, Germany Received: 14 January 2002 / Accepted: 18 February 2002 / Published online: 3 October 2002 Ó Springer-Verlag 2002 Abstract A systematic inventory of actinosporeans and oligochaetes conducted over 3 years at a trout fish farm in Bavaria, Germany, allowed the identification of 12 actinosporeans from five collective groups: four Triactinomyxon (Triactinomyxon nov. types 1–4), two Raabeia (Raabeia nov. types 1, 2), two Echinactino- myxon (E. radiatum, Echinactinomyxon nov. type 1), two Aurantiactinomyxon (A. pavinsis, Aurantiactino- myxon nov. type 1) and two Neoactinomyxum (Neoactinomyxum nov. types 1, 2). Nine forms are novel but can be placed within existing collective groups. All 12 forms were detected in the laboratory in aquarium water associated with farm sediment. However, only four of these could be linked with an oligochaete host. Three families of oligochaetes were identified from the sediment: Tubificidae, represented by eight species, Lumbriculidae with one species and Naididae with two species. Only tubificid oligochaetes were found to host actinosporeans. Introduction Actinosporeans and annelids have been demonstrated to be constituents of the life cycle of a number of my- xosporeans (see Kent et al. 2001). Subsequent to the determination of this connection and in order to un- derstand better the dynamics of the piscine infection, several studies have been conducted which focus on the actinosporean fauna present at sites where a myxospo- rean is pathogenic to wild or farmed fish. Such studies include reports of actinosporeans from: (1) an atlantic salmon (Salmo salar) farm in Scotland where infections with Sphaerospora truttae recur annually (McGeorge et al. 1997), (2) channel catfish (Ictalurus punctatus) ponds in the USA which experience outbreaks of proliferative gill disease (Burtle et al. 1991; Pote and Waterstrat 1993), (3) common carp (Cyprinus carpio) farm ponds in Germany where Sphaerospora renicola is problematic (Großheider and Ko¨rting 1993) and (4) goldfish (Carassius auratus) farm ponds in Japan enzootic for the causative agent of kidney enlargement disease (Yokoy- ama et al. 1993a). The present study was conducted to provide an inventory of the actinosporeans and oligochaetes from a rainbow trout (Oncorhynchus mykiss) farm in Bavaria, Germany, endemic for proliferative kidney disease (PKD), to investigate the possible correlation between these organisms and the disease. This field work was carried out prior to the knowledge that a typical actinosporean stage and annelid host are not involved in the transmission of PKD. The more recent work of Feist et al. (2001) confirmed that PKD is caused by Tetracapsula bryosalmonae Canning, Curry, Feist, Longshaw and Okamura, 1999, whose primary host is a bryozoan. The exact invertebrate host and infective ‘‘spore’’ stage corresponding to PKD in the fish under the present study are yet to be ascer- tained. Other myxozoans have been recorded from non- farmed fish present in the farm waters, including My- xobilatus gasterostei, Myxobolus cotti, Sphaerospora elegans, S. renicola and Zschokkela nova (unpublished data). The life cycles of M. cotti and S. renicola have been elucidated and involve a triactinomyxon and neoactinomyxum actinosporean stage, respectively (El-Matbouli and Hoffmann 1989; Molna´r et al. 1999). Here, we detail the actinosporeans and oligochaetes collected over 3 years from a Bavarian trout farm. Parasitol Res (2003) 89: 170–184 DOI 10.1007/s00436-002-0683-7 M. Oumouna Æ S.L. Hallett Æ R.W. Hoffmann M. El-Matbouli (&) Institute of Zoology, Fish Biology and Fish Diseases, Kaulbachstrasse 37, Munich 80539, Germany E-mail: elmatbouli@zoofisch.vetmed.uni-muenchen.de Fax: +49-89-2805175 Present address: M. Oumouna Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA