Developmental stages of fish blood flukes, Cardicola forsteri and Cardicola opisthorchis (Trematoda: Aporocotylidae), in their polychaete intermediate hosts collected at Pacific bluefin tuna culture sites in Japan

Abstract

Farming of Pacific bluefin tuna (PBT), Thunnus orientalis, is a rapidly growing industry in Japan. Aporocotylid blood flukes of the genus Cardicola comprising C. orientalis, C. opisthorchis and C. forsteri are parasites of economic importance for PBT farming. Recently, terebellid polychaetes have been identified as the intermediate hosts for all these parasites. We collected infected polychaetes, Terebella sp., the intermediate host of C. opisthorchis, from ropes and floats attached to tuna cages in Tsushima, Nagasaki Prefecture, Japan. Also, Neoamphitrite vigintipes (formerly as Amphitrite sp. sensu Shirakashi et al., 2016), the intermediate host of C. forsteri, were collected from culture cages in Kushimoto, Wakayama Prefecture, Japan. The terebellid intermediate hosts harbored the sporocysts and cercariae in their body cavity. Developmental stages of these blood flukes were molecularly identified using species specific PCR primers. In this paper, we describe the cercaria and sporocyst stages of C. opisthorchis and C. forsteri and compare their morphological characteristics among three Cardicola blood flukes infecting PBT. We also discuss phylogenetic relations of the six genera of the terebellid intermediate hosts (Artacama, Lanassa, Longicarpus, Terebella, Nicolea and Neoamphitrite) of blood flukes infecting marine fishes, based on their morphological characters.

Dynamics of Cardicola spp. Infection in Ranched Southern Bluefin Tuna: First Observation of C. orientalis at Transfer

“…Load, suggesting that the intermediate hosts required to complete the blood fluke life cycle are in proximity to aquaculture sites [16,18]. Cardicola forsteri utilises two different terebellid species that are taxonomically close to one another, Longicarpus modestus in Australia and Neomphitrite vigintipes in Japan [16,41,42]. For C. orientalis, the intermediate host was identified in Japan as Nicolea gracilibranchis; however, the intermediate host for this species is yet to be identified in Australia [41].…”

Prevalence and Intensity of Cardicola spp. Infection in Ranched Southern Bluefin Tuna and a Comparison of Diagnostic Methods

“…In Australia, the asexual stages of C. forsteri were found in a single terebellid polychaete, Longicarpus modestus, near SBT pontoon sites [25]. In Japan, life cycles have been elucidated for C. orientalis, C. forsteri and C. opisthorchis with terebellid polychaetes identified as the intermediate host [26][27][28]. Research has also looked to determine spatial and temporal changes of terebellid polychaetes near tuna pontoons, as this can have different implications for potential efforts to control the parasite [29,30].…”