Life cycles of species of Proteocephalus, parasites of fishes in the Palearctic Region: a review

Abstract

The life cycles of species of Proteocephalus Weinland, 1858 (Cestoda: Proteocephalidea) parasitizing fishes in the Palearctic Region are reviewed on the basis of literary data and personal experimental observations, with special attention being paid to the development within the intermediate and definitive hosts. Planktonic crustaceans, diaptomid or cyclopid copepods (Copepoda), serve as the only intermediate hosts of all Proteocephalus species considered. A metacestode, or procercoid, develops in the body cavity of these planktonic crustaceans and the definitive host, a fish, becomes infected directly after consuming them. No previous reports of the parenteral location of metacestodes within the second intermediate host as it is in the Nearctic species P. ambloplitis have been recorded. Thus, the life cycles of Proteocephalus tapeworms resemble in their general patterns those of some pseudophyllidean cestodes such as Eubothrium or Bothriocephalus, differing from the latter in the presence of a floating eggs instead of possessing an operculate egg from which a ciliated, freely swimming larva, a coracidium, is liberated. The scolex of Proteocephalus is already formed at the stage of the procercoid within the copepod intermediate host; in this feature, proteocephalideans resemble caryophyllidean rather than pseudophyllidean cestodes. The morphology of procercoids of individual species is described with respect to the possibility of their differentiation and data on the spectrum of intermediate hosts are summarized. Procercoids of most taxa have a cercomer, which does not contain embryonic hooks in contrast to most pseudophyllidean cestodes. The role of invertebrates (alder-fly larvae — Megaloptera) and small prey fishes feeding upon plankton in the transmission of Proteocephalus tapeworms still remains unclear but these hosts are likely to occur in the life cycle. Data on the establishment of procercoids in definitive hosts, morphogenesis of tapeworms within fish hosts, and the length of the prepatent period are still scarce and new observations are needed. Whereas extensive information exists on the development of P. longicollis (syns. P. exiguus and P. neglectus), almost no data are available on the ontogeny of other taxa, in particular those occurring in brackish waters (P. gobiorum, P. tetrastomus). The morphology of P. cernuae and P. osculatus procercoids from experimentally infected intermediate hosts is described for the first time.

Associations between fish reproductive cycle and the dynamics of metazoan parasite infection

“…The presence and efficiency of crustacean intermediate hosts and the transfer to definitive hosts are crucial for the seasonal dynamics of Proteocephalus species (Kennedy and Hine 1969;Scholz 1999;Hanzelova´and Gerdeaux 2003).…”

Seasonal occurrence of the tapeworm Proteocephalus longicollis and its transmission from copepod intermediate host to fish

“…Developmental stages of C. abyssorum prealpinus copepods and their infection with tapeworms (Tables 2, 3) were determined under the microscope using 70-180· magnification. Fully developed tapeworm larvae (plerocercoids) found in copepods were differentiated using species-specific characters of the scolex (Scholz 1991(Scholz , 1999Sysoev et al 1994). The scolex of P. neglectus (synonym P. longicollis) larvae is identical in its overall appearance to that in the adult worm; it is spherical or semi-spherical, suckers are large and situated at the anterior end of the scolex, and the apical sucker is vestigial but relatively large and oval.…”

“…Although numerous data on the morphology of Proteocephalus cestodes and their development under experimental conditions have been gathered (Wooten 1974;Priemer 1980;Priemer and Goltz 1986;Scholz 1991Scholz , 1993Scholz , 1999Sysoev et al 1994), information about the occurrence and spatial/time distribution of metacestodes (plerocercoids) in natural populations of intermediate hosts is still scarce (Sysoev 1983(Sysoev , 1987Hanzelova´et al 1989). Limited data are also available on the transmission of Proteocephalus metacestodes from copepods to fish and their establishment and morphogenesis in the definitive hosts (see Scholz 1999 for review).…”

“…Copepods acquire infection through eating eggs containing oncospheres and the definitive fish host becomes infected after consuming infected intermediate hosts (Scholz 1999). Life cycles of Proteocephalus tapeworms resemble those of pseudophyllidean cestodes with two-host life cycles such as Eubothrium and Bothriocephalus (Boyce 1974;Hanzelova´and Ž itnˇan 1986;Marcogliese and Esch 1989;Robert and Gabrion 1991;Marcogliese 1995;Scholz 1997;Hanzelova´et al 2002).…”

“…Limited data are also available on the transmission of Proteocephalus metacestodes from copepods to fish and their establishment and morphogenesis in the definitive hosts (see Scholz 1999 for review).…”