Morphological study and molecular epidemiology of Anisakis larvae in mackerel fish

Abstract

Objective: To examine and study the morphology, epidemiology, and molecular phylogeny of Anisakis larvae in blue mackerel [Scomber australasicus (Cuvier, 1832)] and Indian mackerel [Rastrelliger kanagurta (Cuvier, 1816)] using light microscope, scanning electron microscope, molecular phylogeny, and species delimitation methods for confirmation and investigation of Anisakis species and their evolutionary relationship. Methods: A total of 90 fish (45 per species) were purchased from a department store in Chiang Mai, Thailand. Anisakis samples were investigated for morphological characteristics using light and scanning electron microscopes. Molecular phylogeny and species delimitation methods based on the cox2 gene were performed. Results: The prevalence, mean intensity (Mean±SEM), and mean abundance of Anisakis larvae (Mean±SEM) in blue mackerel were 77.78%, 6.74±1.320, and 5.24±1.107, respectively, and in Indian mackerel, these values were 13.33%, 2.50±0.764, and 0.33±0.159, respectively. Scanning electron microscopy showed the detail of morphological characteristics and provided the different shapes of mucron and excretory pores in Anisakis larvae congruent with the phylogenetic tree. The species tree was congruent with the phylogenetic tree. Conclusions: The prevalence, mean intensity, and mean abundance of Anisakis larvae were higher in blue mackerel. To the best of our knowledge, this is the first time that Anisakis pegreffii was found in blue mackerel in Thailand. The phylogenetic tree also supported the morphological data of Anisakis larvae. However, species delimitation based on cox2 revealed 1-3 possible cryptic species in this genus. Anisakis spp. contamination of fish products is unpleasant and a health concern considering human infection with larvae (anisakiasis) arises.