Bull. Eur. Ass. Fish Pathol., 31(4) 2011, 147 First report of the occurrence of marine actinosporean stages (Myxozoa, Myxosporea) in Nereis diversicolor from Tunisian waters S. Bahri Université Tunis-El Manar, Faculté des Sciences de Tunis, Département de Biologie, 2092 El Manar II, Tunisie Abstract Tetractinosporean stages have been found in the marine polychaete Nereis diversicolor O. F. Müller 1776 collected from Lake Ichkeul in Tunisia. Earliest stages and pansporocysts with immature actinospores were found in the coelomic fluid of the polychaetes. The prevalence of infection was 2.8% (4 of 142 worms were infected). This is the first record of actinosporean developmental stages in marine polychaete from Tunisia. Introduction Since the discovery of the alternate host of Nereis diversicolor as invertebrate host (Rangel Myxobolus cerebralis, a parasite of salmonid et al., 2009) and an unicapsulactinomyxon type fish, by Markiw and Wolf (1983) and Wolf and infecting the polychaete Diopatra neapolitana Markiw (1984), 33 life cycles have been de- and linked to the myxospore Enteromyxum sp. scribed for freshwater myxosporeans which (Rangel et al., 2011). have been shown to use the oligochaetes, the bryozoans and the polychaetes as invertebrate In addition, other marine actinospores have been hosts (Lom and Dyková, 2006). described from marine oligochaetes (Hallett et al., 1998, 1999, 2001; Hallett and Lester, 1999), However, in the marine environment, only 5 life polychaetes (Køie, 2000, 2002, 2005) and also cycles have been described for marine myxo- from sipunculids (Ikeda, 1912), that have not zoan species. They concerned Ellipsomyxa gobii been linked to a myxospore stage. Direct life Køie 2003, which uses the polychaetes Nereis cycles without the need for an intermediate diversicolor and N. succinea as invertebrate hosts host have also been shown, e.g., Enteromyxum (Køie, 2000; Køie et al., 2004); Gadimyxa atlantica leei (Diamant, 1997). Køie, Karlsbakk and Nylund, 2007, that occurs in the polychaetes Spirorbis spp. (Køie et al., 2007); In the present work we report the different devel- Ceratomyxa auerbachi Noble 1950, which infects opmental actinosporean stages that occur inside the polychaete Chone infundibuliformis (Køie et the invertebrate host Nereis diversicolor collected al., 2008); Zschokkella mugilis Sitjà-Bobadilla & from a brackish lagoon in Tunisia. Data on the Alvarez-Pellitero 1993, that uses the polychaete prevalence of infection are also provided. * Corresponding author’s e-mail: [email protected] Bull. Eur. Ass. Fish Pathol., 31(4) 2011, 148 Materials and methods pansporocysts showed signs of asynchrony in Nereis diversicolor were collected at 0.5 m depth the development. The pansporocysts observed in Lake Ichkeul situated in Northeast of Tunisia in one polychaete were elongated, measuring (37°9’N, 9°39’E). A total of 142 specimens were 30-40 x 20-30 µm (Figures 2a, 2b). The pans- examined from May to July 2010 for the pres- porocyst wall was composed by two enveloping ence of actinosporeans. The worms were kept cells with flat nuclei. One pansporocyst showed in oxygenated aquaria refrigerated at 6°C in a subspherical actinospore, slightly flattened filtered water and fed with fish flake food until apically and spherical basally (Figure 2b). The their examination. To find and isolate actino- polar capsules were spherical. sporean stages from the infected polychaetes, the coelomic fluid of the worms was examined According to the descriptions provided in Lom using the methods of Rangel et al. (2009). Mor- and Dyková (2006), the present actinosporean phological descriptions and measurements of belong to the actinospore type Tetractinomyxon actinosporean stages were made according to (Ikeda, 1912) which is characterized by rounded Lom et al. (1997). Measurements and photo- tetrahaedroid spores with polar capsules at graphs of pansporocysts and earliest stages were the apex of the tetrahaeder and which form taken from fresh material using a microscope pansporocysts divided into two halves by a (Nikon E600) with contrast interference. central strangling. Results and discussion Marine actinosporean stages have been found Of the 142 Nereis diversicolor collected from in numerous invertebrate hosts such as the Lake Ichkeul, four specimens (2–10 cm long) sipunculid worms (Ikeda, 1912), the marine were infected with actinosporeans (prevalence oligochaetes (Hallett et al., 1998, 1999, 2001; of 2.8%). Three of them carried earliest devel- Hallett and Lester, 1999) and the marine poly- opmental stages (Figure 1a-c) and one 2 cm chaetes (Køie, 2000, 2002, 2005; Rangel et al., long polychaete contained numerous immature 2011). However, only a few species have been pansporocysts (Figure 2a-b). Free spores were linked to a particular myxosporean infecting not found in the examined polychaetes. fish. Indeed, the prevalence of infection in the alternate host was very low in the current study. The actinosporean earliest stages observed in And, similar to the studies of Rangel et al. (2009), the coelomic fluid were round-shaped cells, the mature actinospores were released only 12-14 µm in diameter (Figure 1a) and other cells when the polychaete died which limits experi- were in division (Figures 1b, 1c). According to mental challenges to fish. Rangel et al. (2009) these cells correspond to the end of the schizogony and the beginning of the In agreement with Kent and Lom (1999), the gametogony. The observed pansporocysts were actinospore stages found in the current study in sporogony (Figures 2a, 2b). They contain should be referred to as Tetractinomyxon type eight immature actinospores and seem to be 1 of Bahri (2011) until mature actinospores are in phase that occurs between the seventh and found and molecular and experimental studies the tenth day of development. However, some are conducted to link fish and polychaete stages Bull. Eur. Ass. Fish Pathol., 31(4) 2011, 149 Figure 1. Earliest developmental actinosporean stages (a-c). a. One cell. b. Two cells. c. Four cells. (Bar: 10 µm). Figure 2. Immature pansporocysts (a-b) observed in the coelomic fluid ofNereis diversicolor. a. pansporocyst containing eight immature actinospores and divided into two halves. b. presence of mature actinospore in the pansporocyst showing the polar capsules. (Bar: 10 µm). Ichkeul Lake, Tunisia. Journal of Eukaryotic of the parasites. In particular, focus on the six Microbiology 50, 417-424. species of the genus Myxobolus collected from Diamant A (1997). Fish-to-fish transmission of two species of mullet (Mugil cephalus and Liza a marine myxosporean. Diseases of Aquatic ramada) in the Ichkeul Lake (Bahri and Marques, Organisms 30, 99-105. 1996; Bahri et al., 2003). Hallett SL and Lester RJG (1999). Actinosporeans (Myxozoa) with four developing spores within References a pansporocyst: Tetraspora discoidea n. g. n. sp. Bahri S and Marques A (1996). Myxosporean and Tetraspora rotundum n. sp. 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