Occurrence ofTerranovalarval types (Nematoda: Anisakidae) in Australian marine fish with comments on their specific identities
Pseudoterranovosis is a well-known human disease caused by anisakid larvae belonging to the genusPseudoterranova. Human infection occurs after consuming infected fish. Hence the presence ofPseudoterranovalarvae in the flesh of the fish can cause serious losses and problems for the seafood, fishing and fisheries industries. The accurate identification ofPseudoterranovalarvae in fish is important, but challenging because the larval stages of a number of different genera, includingPseudoterranova,TerranovaandPulchrascaris, look similar and cannot be differentiated from each other using morphological criteria, hence they are all referred to asTerranovalarval type. Given thatTerranovalarval types in seafood are not necessarilyPseudoterranovaand may not be dangerous, the aim of the present study was to investigate the occurrence ofTerranovalarval types in Australian marine fish and to determine their specific identity. A total of 137 fish belonging to 45 species were examined.Terranovalarval types were found in 13 species, some of which were popular edible fish in Australia. The sequences of the first and second internal transcribed spacers (ITS-1 and ITS-2 respectively) of theTerranovalarvae in the present study showed a high degree of similarity suggesting that they all belong to the same species. Due to the lack of a comparable sequence data of a well identified adult in the GenBank database the specific identity ofTerranovalarval type in the present study remains unknown. The sequence of the ITS regions of theTerranovalarval type in the present study and those ofPseudoterranovaspp. available in GenBank are significantly different, suggesting that larvae found in the present study do not belong to the genusPseudoterranova, which is zoonotic. This study does not rule out the presence ofPseudoterranovalarvae in Australian fish asPseudoterranova decipiens Ehas been reported in adult form from seals in Antarctica and it is known that they have seasonal presence in Australian southern coasts. The genetic distinction ofTerranovalarval type in the present study fromPseudoterranovaspp. along with the presence of more species of elasmobranchs in Australian waters (definitive hosts ofTerranovaspp. andPulchrascarisspp.) than seals (definitive hosts ofPseudoterranovaspp.) suggest thatTerranovalarval type in the present study belong to either genusTerranovaorPulchrascaris, which are not known to cause disease in humans. The present study provides essential information that could be helpful to identify AustralianTerranovalarval types in future studies. Examination and characterisation of further specimens, especially adults ofTerranovaandPulchrascaris, is necessary to fully elucidate the identity of these larvae.