A comparative study of the fish parasites Proteocephalus exiguus and P. percae (Cestoda: Proteocephalidae): morphology, isoenzymes, and karyotype

Abstract

The two closely related cestodes Proteocephalus exiguus (= P. neglectus) and P. percae, parasites of coregonid and salmonid fishes and of perch, respectively, were compared using morphological, biochemical, and cytogenetic methods. Three morphological forms of similar appearance were observed in both P. exiguus and P. percae. Although the two species were strikingly similar in general morphological appearance, some of the features analyzed morphometrically (width of scolex, diameter of apical organ, length and width of hermaphroditic proglottis, length of cirrus sac) exhibited consistent differences. Fixed genetic differences distinguish the species at five loci in EST, GOT, and PGM enzymes. Nei's interspecific genetic distance was 0.305. Both species have 18 chromosomes with comparable absolute lengths. However, the morphology of most chromosome pairs differed. On the basis of these results, discriminative characteristics for P. exiguus and P. percae are given.