Molecular evidence for cosmopolitan distribution of platyhelminth parasites of tunas (Thunnus spp.)

Abstract

Global distribution of platyhelminth parasites and their host specificities are not well known. Our hypothesis was that platyhelminth parasites of large pelagic fishes are common around the world. We analysed molecular variation in three different taxa of platyhelminth parasites infecting four species of tunas: yellowfin tuna (Thunnus albacares, Scombridae) from Western Australia, southern bluefin tuna (Thunnus maccoyii, Scombridae) from South Australia, Pacific bluefin tuna (Thunnus orientalis, Scombridae) from Pacific Mexico and northern bluefin tuna (T. thynnus, Scombridae) from two localities in the Mediterranean (Spain and Croatia). Comparisons of ITS2 and partial 28S rDNA demonstrated two congeneric species of blood flukes (Digenea: Sanguinicolidae) from multiple hosts and localities: Cardicola forsteri from southern bluefin and northern bluefin tunas, and Cardicola sp. from Pacific bluefin and northern bluefin tunas; and a gill fluke, Hexostoma thynni (Polyopisthocotylea: Hexostomatidae), from yellowfin, southern bluefin and northern bluefin tunas. Partial 28S rDNA indicates that a second type of fluke on the gills, Capsala sp. (Monopisthocotylea: Capsalidae), occurs on both southern bluefin and Pacific bluefin tunas. This appears to be the first report of conspecific platyhelminth parasites of teleosts with a wide-ranging geographical distribution that has been confirmed through molecular approaches. Given the brevity of the free-living larval stage of both taxa of flukes on the gills (H. thynni and Capsala sp.), we conclude that the only feasible hypothesis for the cosmopolitan distribution of these flatworms is migrations of host tunas. Host migration also seems likely to be responsible for the widespread occurrence of the two species of blood flukes (Cardicola spp.), although it is also possible that these were translocated recently by the spread of infected intermediate hosts.

Eight new species of Siphoderina Manter, 1934 (Digenea, Cryptogonimidae) infecting Lutjanidae and Haemulidae (Perciformes) off Australia

“…Of the fish species reported to harbour species of Siphoderina, only Rachycentron canadum has a cosmopolitan distribution; it is thus possible that S. morosovi, which was reported from R. canadum, may also be widely distributed. Aiken et al (2007) recently reported near cosmopolitan distributions for species of Sanguinicolidae (confirmed by comparative analysis of rDNA sequence data) in bluefin tuna (Thunnus spp. ), so it is clear that trematodes of fishes can be widely distributed.…”

Schistosomatoidea and Diplostomoidea

“…Cardicola forsteri have recently become an emerging pathogen causing massive mortalities in cage-reared southern bluefi n tuna in coastal areas of Australia [ 119 , 120 ]. It has a big potential of further emergence in aquacultures in other parts of the world, being able to infect other tunas, like northern bluefi n suffering from cardicoliasis in Spanish coastal farms [ 100 ]. In Japan, mortality of pacifi c blue tunas is caused by C. orientalis and C. opisthorchis ; in a heavily infected individual, a total number of >4.5 million eggs were estimated in the gills at one side of the fi sh [ 121 ].…”

“…in tuna fi shes ( Thunnus spp.) by molecular approaches [ 100 ]. Prevalence of the fl ukes in fi sh hosts varies greatly among various reports, and apparently, there is no common pattern.…”

Parasites and cleaning behaviour in damselfishes

“…Although A. laguncula has not been reported from any fish family on the GBR other than pomacentrids (reported from 3 species only), it has been recorded in 67 teleost species from 29 families, making it putatively one of the most widespread digeneans with respect to both geographical distribution and host range (Bray and MacKenzie 1990;Bray et al 1993a laguncula is indeed one species, despite its apparent cosmopolitan distribution, as has been previously demonstrated for the tuna-infecting aporocotylid fluke Cardicola forsteri Cribb, Daintith & Munday, 2000(Aiken et al 2007). The same principles may also apply to the other reportedly cosmopolitan species, Lecithaster stellatus.…”

“…(Aiken et al 2007), such widespread species appear to be exceptional. We think it possible, perhaps likely, that Pseudobacciger will prove to comprise a complex of significantly more species than are presently recognised.…”