Endoparasitic Dinoflagellate of the Genus Ichthyodinium Infecting Fertilized Eggs and Hatched Larvae Observed in the Seed Production of Leopard Coral Grouper Plectropomus leopardus

Abstract

-Since 1990, mass mortality of fertilized eggs and hatched larvae of the leopard coral grouper Plectropomus leopardus has occurred repeatedly during its seed production in Okinawa Prefecture. A hitherto unknown protozoan parasite multiplied in the yolk sac in great numbers. The yolk sac of fertilized eggs and hatched larvae eventually burst and parasites were released to sea water. The development of the parasite was briefly described, which is very similar to that of the dinoflagellate Ichthyodinium chabelardi, known to infect yolk of several marine fish larvae in Europe. Based on the similarities of, and minor differences in, the mode of infection, development and SSU rDNA sequence, the parasite is tentatively designated as Ichthyodinium sp. PL (= PL for the abbreviated form of the scientific name for the host). Although the life cycle of the parasite is unknown, the disease outbreak was controlled by rearing the broodstock and incubating fertilized eggs in oxidant-treated seawater. The PCR diagnosis using specific primers designed from part of SSU rDNA sequence of the parasite revealed that disease outbreaks in different years were caused by a single species of parasite. This is the first report of Ichthyodinium infection in tropical fish from the Asia-Pacific region.

Infection by a Protozoan Endoparasite of the genus Ichthyodinium in Embryos and Yolk-sac Larvae of Yellowfin Tuna Thunnus albacares

“…The annual catch of Japanese sardine Sardinops melanostictus in Japan has rapidly dropped since 1989, and various theories on the cause of this phenomenon have been proposed (Kasai et al, 1997), which did not include the effect of the parasitic infection. The sequence of 18S rRNA of the endoparasite detected from leopard coral grouper (Mori et al, 2007) and bluefin tuna Thunnus thunnus (Dr. K. Ishimaru, Kinki University, personal communication) were consistent with that of the parasite in this study, suggesting that the identical endoparasite inhabits the seas or marine fish species worldwide. In a future study, investigation on the occurrence of the infection in Japanese sardine as well as in other fish species by PCR is required to understand the distribution of the parasites.…”

“…Mass mortality of yolk-sac larvae of yellowfin tuna observed in this study was apparently caused by the infection of a protozoan endoparasite, and the morphology and pathogenicity of the parasite was similar to that of the protozoan endoparasite of Atlantic sardine Sardina pilchardus in the Bay of Algiers and the Iberian Sea (Hollande and Cachon, 1952;Stratoudakis et al, 2000) and of leopard coral grouper Plectropomus leopardus in Ishigaki Island, Japan (Mori et al, 2007). Morphological characteristics of the parasite from Atlantic sardine, including the initial number of infected parasite (1-3 in number), the maximum size of the parasite (about 100 mm in major axis) and numerous number of the parasite at 24 h post-spawning in the embryo as well as the existence of swimming stage (round shaped with 2 flagellae, 15 -20 mm in diameter), were identical to those of the parasite in this study.…”

“…However, the number of the parasite infected in a yolk sac of Atlantic cod and turbot was low, and the yolk sac did not show any opaque coloration. In Japan, a similar infection was also observed during the seed production of leopard coral grouper Plectropomus leopardus between 1990 and 2004 (Mori et al, 2007) and of bluefin tuna Thunnus thunnus in 2004 (Dr. K. Ishimaru, Kinki University, personal communication). The yolk sacs of infected fish showed opaque color and finally burst, causing death due to heavy infection.…”

“…The templates were amplified with TaKaRa Taq Polymerase Hot Start Version (TaKaRa) and a primer set, 1321f (CCGGAACTTT-AGAGTATCGG) and 1679r (TCGGTTCAGACTGAAC-CAAG), which was designed from the 18S rRNA sequence of the protozoan endoparasite detected from yolk-sac larvae of leopard coral grouper produced at Yaeyama Station, Seikai National Fisheries Research Institute, Fisheries Research Agnecy, in southern Japan (Mori et al, 2007). The size of amplicon by this primer set was 359 bp.…”

The Environmental Clade LKM11 and Rozella Form the Deepest Branching Clade of Fungi

“…Alveolate sequences from environmental Groups I and II, which are highly abundant in marine clone libraries (Epstein and López-García 2008;Guillou et al 2008), have only recently had their taxonomic identification recognised as Syndiniales. Group I includes the genera Duboscquella (Harada et al 2007), Ichtyodinium (Mori et al 2007) and a Red Plasmodial parasite (Skovgaard and Daugbjerg 2008), whereas Group II comprises sequences of the genera Syndinium, Amoebophrya and Hematodinium (Skovgaard et al 2005). All of the known species of Group I and II alveolates are parasites/ parasitoids of marine organisms (radiolaria, dinoflagellates but also copepods and teleost fishes) and this lifestyle is likely extensive to the two groups.…”