Intraspecific Genetic Variation of Anisakis typica in Indian Mackerel Caught from the Gulf of Thailand, Samut Songkhram Province

Abstract

Anisakis nematodes infecting Indian mackerel (Rastrelliger kanagurta) were initially discovered in Thailand in our preliminary investigation. Nevertheless, the species of Anisakis collected has not been determined nor has its genetic variation been researched. Thus, this study aimed to molecularly identify the species of Anisakis specimens using the internal transcribed spacer (ITS) region of ribosomal DNA sequences. In addition, the intraspecific genetic variation was also determined using mitochondrial cytochrome oxidase subunit II (COII) gene sequences. The phylogenetic relationships of the ITS region classified all samples into Anisakis typica; however, the genetic variation between them could not be distinguished. By contrast, the phylogenetic tree analysis of the COII region identified all samples as A. typica, with 17 different haplotypes by 66 polymorphic sites and five of the substitutions resulted in amino acid change. Additionally, the distribution pattern of the COII region can be separated into two groups between South America and Asian countries. All our haplotypes belong to Asian countries. Compared with the two genetic markers used in this investigation, COII appears to be a better candidate for studying genetic variation sensitive to environmental changes and intermediate or definitive host behavioral changes.

Article Review: Identifications and Geographic Distribution of Six Anisakis Species (Nematoda: Anisakidae) in Indonesia

“…Anisakis typica is the most common species in Indonesia and is also present in Thailand (Chaiphongpachara et al, 2022), Papua New Guinea (Koinari et al, 2013), and the Philippines (Quiazon et al, 2013). Anisakis typica, which belongs to the families Delphinidae, Phocoenidae, and Pontoporidae, is a frequent parasite of numerous dolphin species from warmer temperate and tropical regions (Mattiucci et al, 2002).…”

“…Rastrelliger sp. (R. kanagurta and R. branchysoma) are indicated an important intermediate host of A. typica in Southeast Asia, this fish is a pelagic schooling fish widely distributed in the Indian Ocean and Indo-West Pacific region (Chaiphongpachara et al, 2022).…”

“…There are no reports of Anisakis in Southeast Asian tropical nations like Brunai, Myanmar, Cambodia, and Vietnam (Wiwanitkit and Wiwanitkit, 2016). There are some reports on parasite study in fish in Thailand (Chaiphongpachara et al, 2022) and Philippines (Quiazon et al, 2013). Hemsrichart (1993) and Amir et al (2016) both reported on the first anisakiasis case in Thailand and Malaysia, respectively.…”