Wojciech PIASECKI *And Ewa KUŹMIŃSKA
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ACTA ICHTHYOLOGICA ET PISCATORIA (2007) 37 (2): 117–128 DOI: 10.3750/AIP2007.37.2.09 DEVELOPMENTAL STAGES OF ACHTHERES PERCARUM (CRUSTACEA: COPEPODA), PARASITIC ON EUROPEAN PERCH, PERCA FLUVIATILIS (ACTINOPTERYGII: PERCIFORMES) Wojciech PIASECKI *and Ewa KUŹMIŃSKA Division of Fish Diseases, Faculty of Food Sciences and Fisheries, Agricultural University of Szczecin, Poland Piasecki W., Kuźmińska E. 2007. Developmental stages of Achtheres percarum (Crustacea: Copepoda), par - asitic on European perch, Perca fluviatilis (Actinopterygii: Perciformes). Acta Ichthyol. Piscat. 37 (2): 117–128 . Backg round. Achtheres percarum is an important copepod parasite (Crustacea: Copepoda) of European perch. Adult females permanently attach to the gill arches, roof of the mouth, tongue, and gill filaments. Attachment, at the latter site, may result in necrosis and epithelial hypertrophy, both compromising fish respiration during oxygen deficiencies. Adult males can move freely on gills of perch. To date there has been no published record of the complete set of developmental stages of this fish parasite. Provision of such may have practical implica - tions for freshwater ichthyopathology, for example helping to monitor the dynamics of the parasite’s populations. It may also provide useful information regarding copepod phylogenetics. Materials and Methods. Early developmental stages (nauplius and copepodid) of A. percarum were acquired through incubation of eggs within egg sacs of females collected from European perch, Perca fluviatilis L., caught commercially in 1994 in Lake Dąbie, Szczecin, Poland. All subsequent larval stages were collected from gills of perch caught in the same lake, in 1990. All copepods were fixed and preserved in 75% ethanol. A modified “wooden slide” method was used to observe the collected developmental stages in a suspended drop of lactic acid, using a compound microscope. Specimens were stained in lignin pink and morphologic details of were drawn using a drawing tube. Results. The life cycle of A. percarum consists of 7 developmental stages, separated by moults (nauplius, cope - podid, chalimus I, chalimus II, chalimus III, chalimus IV, and adult). The nauplius hatches from the egg and quickly moults into the copepodid. Both stages are free swimming and the copepodid is the infective stage, attaching to the host’s gill filaments, through the frontal filament. The subsequent chalimus stages (I through IV) “inherit” the copepodid’s frontal filament, modifying its proximal end, such that the structure of the proximal end of the frontal filament explicitly identifies the stage of a chalimus. Two adult males were found attaching, by means of claws of its maxillipeds, to the frontal filament, left over by previous stages. Conclusion. The number of developmental stages of A. percarum determined within the presently reported study is consistent with that hitherto found in the life cycles of other lernaeopodids. Keywords: morphology, developmental stages, Achtheres percarum , fish parasite, copepod, perch, Perca fluviatilis INTRODUCTION Achtheres percarum von Nordmann, 1832 is a para - on its host (Piasecki, unpublished). Kozikowska et al. sitic copepod that infects European perch, Perca fluvi - (1956) described and illustrated lesions associated with atilis L. The parasite shows distinct sexual dimorphism. A. percarum infections on perch, said lesions (necrotic The adult female attaches to the host using bulla and changes and tissue erosion) attributed to only those elongate arm-like second maxillae (Kozikowska et al. female copepods, found on gill filaments. Epithelium of 1956). Females attach to gill arches, roof of the mouth, neighbouring gill filaments, disturbed by these copepods, tongue, and rarely to gill filaments. The adult male is dis - showed signs of hyperplasia, fusion of gill filaments, and tinctly smaller than the adult female and can move about substantial thickening of gill lamellae. Achtheres sandrae the surface of fish gills (Piasecki et al. 2006). Unlike in Gadd, 1901, infecting zander, Sander lucioperca (L.) the majority of other lernaeopodids (Lernaeopodidae), have recently been declared a valid species by Kempter the male of A. percarum is capable of independent living et al. (2006). * Correspondence: Dr hab. Wojciech Piasecki, prof. nadzw., Zakład Chorób Ryb, Wydział Nauk o Żywności i Rybactwa, Akademia Rolnicza w Szczecinie, ul. Kazimierza Królewicza 4, 71-550 Szczecin, Poland, phone: +4891-423-1061 ext. 226, fax: +4891-423-1347, e-mail: [email protected] 118 Piasecki and Kuźmińska The morphology of adult females of A. percarum was and a harder, well stained “hard plug” with pocket-like described by Kabata (1979) while the morphology of canals for hosting the claws of the next stage’s second males of this copepod—by Piasecki et al. (2006). maxillae (Fig. 65). The glue lump is attached to the orig - The developmental stages of Achtheres percarum inal “plug” at the proximal end of the filament. All pre- have not been described, except for its free-swimming moult chalimi (except chalimus IV female) featured a dis - stages (von Nordmann 1832, Claus 1861) and chalimus tinctly stained (in lignin pink) “plug” in their frontal area. I stage (Claus 1861). Post-moult specimens din not have “plugs” and the “age” The presently reported study constitutes the first of respective stages was marked by the advancement of account on a complete set of developmental stages of the plug formation. Thus, the blunt claws of the second Achtheres percarum , parasitizing European perch. maxillae of chalimus I were inserted into the original “plug” of the proximal filament’s end, unchanged since MATERIALS AND METHODS its extrusion by the copepodid (Figs. 18, 23, 64). The fil - To obtain nauplii and copepodids of A. percarum , nat - ament of chalimus II featured two “plugs” (Figs. 28, 33), urally infected perch were purchased (autumn 1994, chalimus III—three “plugs” (Figs. 39, 44, 66), and chal - spring 1995) from commercial fishermen stationed at imus IV—four “plugs” (Figs. 49, 55, 60, 67). The frontal Stołczyn and operating on Lake Dąbie, Szczecin, Poland. organs of female chalimus IV produced no plug. No signs Ovigerous females of A. percarum were collected from of the bulla production, needed by the female parasite at the perch and those with pigmented eggs were placed in adult stage, were observed in the collected specimens of 100-mL glass beakers filled with water. The water was chalimus IV female. The sexual dimorphism was first vis - replaced twice a day. The processes of hatching, as well ible at the stage of chalimus IV (Figs. 49, 60). Frontal as the first moulting, were periodically monitored under a organs of some male chalimus IV secreted new plug (Fig. dissecting microscope. All subsequent larval stages of A. 67), but no chalimus V was observed, holding the frontal percarum , representing the parasitic phase of develop - filament featuring 5 plugs. Instead, two cases of the adult ment, were collected in April 1990 and in April 1995 male were observed, holding the four-plug filament end directly from commercially caught perch captured in Lake by means of its maxillipeds (not second maxillae!) (Fig. Dąbie. Copepods were fixed and preserved in 75% 68). Only the tips of mandibles in all chalimus stages were ethanol, stained in lignin pink and observed in a suspend - inserted between labium and labium into the mouth cone. ed drop of lactic acid, a modification of the “wooden slide They could be easily withdrawn during moulting. method” of Humes and Gooding (1964) was used to study Nauplius . Females of A. percarum bear prominent, the morphology of all larval stages, using a compound long, multiseriate egg sacs. The embryonic development of microscope (Olympus BX50). Details of morphology larvae within the egg sacs is marked by progressive pig - were drawn using a drawing tube of the microscope. mentation of these eggs. Shortly before hatching, the nau - Terminology used to describe the morphology of lar - plius (first larval stage) is well visible inside the egg shell val stages follows that of Kabata (1979) (with the excep - (Fig. 1). At the moment of hatching the nauplius is ready to tion of caudal rami). moult, such that inside the cuticle of nauplius a fully formed copepodid can be seen (Figs. 2, 3). The copepodid, RESULTS crammed into the tight semispherical confinement of the The life cycle of Achtheres percarum consists of the nauplius cuticle, is twisted into an s-shape with its abdomen following stages: nauplius, copepodid, chalimus I, chal - bent dorsally (Fig. 2). The copepodid promptly started to imus II, chalimus III, chalimus IV and adult. The nauplius emerge form the nauplius cuticle after hatching, however, (Figs. 1–5) and copepodid (Figs. 6–17) are free swim - the moulting process was delayed (indefinitely in some ming. The copepodid is infective and all subsequent lar - cases) under conditions in some of our study beakers . val stages (each referred to as a chalimus) are attached to Morphology of nauplius . Oval, unsegmented body at the gill filaments of the host by means of a long, partly pre-moult stage. Body wider in dorsal view than in lateral coiled frontal filament. The adult female is permanently view (cf. Figs. 2, 3) (Total length 319 ± 6 µm; 313–328 µm; attached to the host at one location by means of a mush - n = 6). Fully formed frontal filament visible inside body room-shaped bulla. The adult male does not attach itself (Figs. 2, 3). Distinct pigment pattern visible inside body permanently at one location on the host. (not illustrated). Anterior part of body with two pairs of All larval stages collected from the gills of perch were setose, swimming appendages: first antenna and second identified as chalimus I, chalimus II, chalimus III, chal - antenna. Posterior end of body without balancers. First imus IV (Figs. 18–67, 69, 70). They were attached by antenna (Fig. 4), uniramous, unsegmented, subcylindrical, means of the frontal filament to the gill filaments. The digitiform, surmounted with two large, equal in length structure of the proximal part of the filament permitted setae.