Parasites of Loligo gahi from waters off the Falkland Islands, with a phylogenetically based identification of their cestode larvae

Abstract

One thousand and ninety-six longfin Patagonian squid, Loligo gahi, were collected from waters off the Falkland Islands over a period of 1 year and 4 months and examined for helminths. Cestode and Anisakis sp. (Nematoda) larvae were present throughout the study, but occurred at low rates. The pooled data showed prevalences of 5.75 and 2.46%, respectively. An adult digenean, Derogenes varicus, was found in a single instance and was thus considered an accidental infection. Parasite parameters were not significantly correlated with either host sex or seasonality. Stomach contents of the squid revealed a highly varied diet, although krill, amphipods, and chaetognaths were the dominant prey items. To aid in the identification of the cestode larvae, a subsample of 14 plerocercoids was characterized for the D2 variable region of the nuclear lsrDNA gene and compared with both published cestode lsrDNA sequences as well as that of six additional adult tetraphyllidean cestode species sequenced herein. Direct sequence comparison showed that 12 of the 14 plerocercoids were identical with each other and differed by a single transition (of a total of 658 base pairs) from the tetraphyllidean Clistobothrium montaukensis, and another plerocercoid differed by two transitions from the trypanorhynch Grillotia erinaceus. The remaining pleroceroid sequence was identified through phylogenetic analysis as being closer to the tetraphyllidean Ceratobothrium xanthocephalum than to any other taxon analyzed, but may not be congeneric, given its relatively high degree of divergence from C. xanthocephalum.