THE BIOLOGY OF ARGULUS SPP. (BRANCHIURA, ARGULIDAE) IN JAPAN: A REVIEW BY KAZUYA NAGASAWA1) Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, 739-8528 Japan ABSTRACT Branchiurans of the genus Argulus are ectoparasites of freshwater and marine fishes. A total of nine species of this genus has been reported from Japan: four freshwater species (A. americanus, A. coregoni, A. japonicus,andA. lepidostei) and five marine species (A. caecus, A. kusafugu, A. matuii, A. onodai,andA. scutiformis). This paper reviews various aspects of the biology of these nine Argulus species, particularly A. japonicus and A. coregoni, in Japan. A. japonicus is usually found on cyprinid fishes, while A. coregoni prefers salmonid fishes. These species usually overwinter as eggs, and after hatching in spring, they abundantly infect their hosts from spring to fall. These species can cause disease problems in fish farms. INTRODUCTION Branchiurans of the genus Argulus Müller, 1785 (Arguloidea: Argulidae) are ectoparasites of freshwater and marine fishes (Yamaguti, 1963). This genus comprises more than 120 species, which accounts for about 85% of the known species in the subclass Branchiura (Kabata, 1988). Argulid branchiurans can cause disease problems and mortality of fishes in aquaculture and aquaria. This paper reviews various aspects of the biology of Argulus spp. in Japan, especially A. japonicus and A. coregoni that have been well studied there. Due to limited restrictions, many papers cannot be not cited in this review, and as such, Nagasawa (2009) should be consulted for further information on the literature. The fish names used here are those recommended by Nakabo (2002). 1) e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2011 New frontiers in crustacean biology: 15-21 16 CRM 015 – Akira Asakura et al. (eds.), NEW FRONTIERS IN CRUSTACEAN BIOLOGY ARGULUS SPP. FOUND IN JAPAN Nine species of the genus Argulus are known to occur in Japan (Nagasawa, 2009): four freshwater species (A. americanus Wilson, A. coregoni Thorell, A. japonicus Thiele, and A. lepidostei Kellicott) and five marine species (A. caecus Wilson, A. kusafugu Yamaguti & Yamasu, A. matuii Sikama, A. onodai Tokioka, and A. scutiformis Thiele). Of these, A. americanus and A. lepidostei are not native to Japan, as they were introduced from North America by ornamental fish trade (Tsutsumi, 1968; Shimura & Asai, 1984). These two species were found only in aquaria. Unspecified Argulus have been also reported from freshwater and marine fishes in Japan (Nagasawa, 2009). BIOLOGY OF ARGULUS JAPONICUS IN JAPAN Argulus japonicus was originally but poorly described by Thiele (1900) based on a female specimen collected in Tokyo (no host information was available). This species was soon described in details by the same author (Thiele, 1904) using specimens from Yokohama. Some other authors also described the species from Japan (see Nagasawa, 2009 for the literature). Cyprinid fishes (family Cyprinidae) are its preferred hosts, i.e., common carp and koi carp Cyprinus carpio, goldfish Carassius auratus, silver crucian carp C. auratus langsdorfi, Japanese crucian carp C. cuvieri, unspecified crucian carp Carassius sp., silver carp Hypophthalmichthys molitrix, and bighead carp Aristichthys nobilis (Nagasawa, 2009). As the species was also found on “many other freshwater fishes” (Tokioka, 1936a), it can perhaps infect fishes of other families as well. Nonetheless, this parasite may prefer certain cyprinid species, because experiments have shown that it more heavily infects the common carp and the Japanese crucian carp as compared to the silver carp (Kimura, 1970). The attachment site of the species is the body surface of its hosts. It can swim in the water to transfer to other hosts, and as such, free-living individuals have been collected in plankton samples (Kimura, 1970; Nagasawa et al., 2009). Argulus japonicus is native to East or Southeast Asia, but it has been introduced to many regions of the world, except Antarctica (Poly, 2008). In Japan, it has been reported from Hokkaido and central and western Honshu only (Nagasawa, 2009). As cyprinids and other freshwater fishes occur in southern Japan, such as Shikoku, Kyushu and the Ryukyu Islands, the species is likely to be present there as well..