Anisakis infections in lantern fish (Myctophidae) from the Arabian Sea: A dual role for lantern fish in the life cycle of Anisakis brevispiculata?

Data on geographic distribution and life cycles of parasitic nematodes of the genus Anisakis in tropical oceanic regions are extremely scarce. Myctophids (lantern fishes) are a key component of mesopelagic trophic webs and could play a significant role in the transmission of Anisakis spp. in these regions. We examined Anisakis infections in a sample of 160 myctophids collected in three localities from the Indian Exclusive Economic Zone (Arabian Sea) in 2015–16. Due to the poor condition of fish, a combination of morphological data and molecular barcoding was used to identify myctophids. Of the 104 specimens that could be identified at least to genus level, 75 (72.1%) were assigned to Diaphus spp. A total of 131 Anisakis larvae were collected from the fish sample (prevalence: 52.5%). One larva was identified as type I, 114 as type II, and 16 larvae could not be assigned to either type. The morphology of all type II larvae conformed to the recent diagnosis of Anisakis brevispiculata. DNA could be obtained only from four larvae, and phylogenetic analyses based on mtDNAcox2 confirmed the identification. Anisakis brevispiculata is specific to dwarf and pygmy sperm whales (Kogiidae), which feed on mesopelagic cephalopods and marginally on myctophids. Therefore, myctophids could play a dual role in the transmission of A. brevispiculata, as direct prey of kogiids and/or as prey of cephalopods that consume myctophids. The prevalence of A. brevispiculata varied significantly in myctophid samples that were just ~ 265 km apart, suggesting potential local effects on transmission rates.