Morphological and Molecular Characteristics of Anisakis typica Larvae in Two Species of Threadfin Bream, Nemipterus hexodon and N. japonicus, from the Gulf of Thailand

Abstract

The third stage larvae (L3) of <i>Anisakis typica</i> were detected in 2 species of threadfin bream, <i>Nemipterus hexodon</i> and <i>N. japonicus</i>, from the Gulf of Thailand, and were morphologically and molecularly characterized. Total 100 threadfin breams, 50 <i>Nemipterus hexodon</i> and 50 <i>N. japonicus</i>, were examined with naked eyes after the opening of abdominal cavity with scissors. Almost all infected larvae remained alive and active even the fish were transported for 1-2 days. Anisakid larvae were exclusively distributed in the body cavity and rarely in the liver. The prevalence of <i>A. typica</i> L3 were 68.0% and 60.0% in <i>N. hexodon</i> and <i>N. japonicus</i> and their infection intensities were 3.5 and 4.2 per fish infected each. Morphological and morphometric analysis were performed by viewing specimens under both a light microscope and a scanning electron microscope. Interestingly, the protruded mucron of <i>Anisakis typica</i> under SEM showed a distinct cylindrical shape that differed from the cone shape of <i>A. simplex</i>. The protruded mucron could be used to identify <i>A. typica</i> L3 larvae in the future. A comparison of the ITS1-5.8S-ITS2 rDNA nucleotide sequences of these species revealed high blast scores with <i>A. typica</i>. Conclusively, it was confirmed that <i>A. typica</i> L3 are prevalent in threadfin breams from the Gulf of Thailand, and their morphological and molecular characters are something different from those of other anisakid larvae, including A. simplex and <i>A. pegreffii</i>.

First morphological and molecular identification of third-stage larvae of Anisakis typica (Nematoda: Anisakidae) from marine fishes in Vietnamese water

“…Vietnamese A. typica were genetically close to those from China, Thailand, Indonesia, Papua New Guinea, and Australia, to make a common group that was separated from another group of America, Brazil, Turkey, and Portugal. Our analysis is in agreement with a previous report that the separation of A. typica populations related to geographical origins ( Tunya et al, 2020 ).…”

“…However, recent studies based on morphological and molecular approaches provided descriptions and microphotographs showing differences between L3 larvae of A. pegreffii and A. typica ( Chen and Shih, 2015 ; Sonko et al, 2019 ). In addition, Tunya et al (2020) suggested that the protruded mucron of L3 larvae can be used to identify anisakid larvae at the species level: the protruded mucron of A. simplex was cone-shape, while that of A. typica was cylindrical-shape, which is narrower and longer than that of A. simplex . According to these, L3 larvae of Anisakis specimens found in this study were identified as A. typica .…”

“…A unique distribution pattern has been known for A. typica which has been reported in warmer temperate and tropical waters (Mattiucci and Nascetti, 2006). In Asian countries, A. typica larvae have been reported in Japan, Korea, China, Taiwan, Indonesia, and Thailand ( Lee et al, 2016 ; Palm et al, 2008, 2017 ; Sonko et al, 2019 ; Tunya et al, 2020 ; Umehara et al, 2010 ; Zhu et al, 2007 ). In the present study, we firstly identified A. typica larvae in Vietnamese water.…”

“…For scanning electron microscopy, Anisakis larvae were prepared according to Madden and Tromba (1976) and Morsy et al (2017) . Larvae were identified according to the reported references ( Berland, 1961 ; Chen and Shih, 2015 ; Mattiucci et al, 2009 ; Sonko et al, 2019 ; Tunya et al, 2020 ).…”

“…Previously, it was not easy to identify anisakid larvae at the species level, because there is a lack of distinct morphological characteristics required for species identification ( Farjallah et al, 2008 ). Recent studies indicated morphological differences between Anisakis species ( Chen and Shih, 2015 ; Sonko et al, 2019 ; Tunya et al, 2020 ). In addition, molecular tools allow the accurate identification of anisakid larvae by using sequences of the internal transcribed spacer (ITS) region of ribosomal DNA ( D’amelio et al, 2010 ; Mattiucci and Nascetti, 2008 ).…”