Morphological study and molecular epidemiology of Anisakis larvae in mackerel fish

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.

Phylogenetic analysis reveals cryptic species diversity within minute intestinal fluke,Stellantchasmus falcatus Onji and Nishio,1916(Trematoda,Heterophyidae)

Objective:To examine the taxonomic boundaries in the Stellantchasmus populations in different hosts and reveal the cryptic speciation of the Stellantchasmus in Thailand based on both morphological and molecular approaches.Methods:Stellantchasmus falcatus(S.falcatus) s.l.was collected from different hosts throughout Thailand.The worms were examined and measured.The nuclear ITS2 gene and the mitochondrial COI gene were used to investigate the S.falcatus s.l.from Dermogenus pusillus and Liza subviridis.Results:Stellantchasmus was one of food-borne trematode that widely distribute throughout Thailand.The comparison of S.falcatus s.l.from Dermogenus pusillus and Liza subviridis indicated a genetic divergence of nuD NA with 3.6% and mtD NA with 19.3%,respectively.Morphological characteristics were fairly different in the ratio of body size,length of prepharynx,and ratio of organ size.Conclusions:Our results provide initial evidence that S.falcatus s.l.from different hosts tend to be a different species based on both molecular and morphological characters.Cryptic species complexes are generally found among parasites that tend to have large populations and/or rapid evolution.The degree of genetic diversity existing would suggest the practice of targeted regimes to design and minimize these lections of anthelmintic resistance in the future.