Vol. 64, 2025

Developmental Stages of an Invasive, Non-indigenous Sea Louce Caligus sclerotinosus Roubal, Armitage and Rhode, 1983 (Copepoda: Siphonostomatoida: Caligidae) Parasitic on Red Sea Bream Pagrus major (Temminck and Schlegel, 1843) Collected from Japanese Waters

¹Graduate School of Integrated Sciences for Life, Hiroshima University, 5–8–1 Minato-machi, Takehara, Hiroshima, 725–0024, Japan. *Correspondence: E-mail: aneesh@hiroshima-u.ac.jp (Aneesh); ohtsuka@hiroshima-u.ac.jp (Ohtsuka)
E-mail: m213413@hiroshima-u.ac.jp (Nishida); kaoriw@hiroshima-u.ac.jp (Wakabayashi); mf09001x@gmail.com (Adachi)
²Fisheries Laboratory, Blue Innovation Division, Seto Inland Sea Carbon-neutral Research Center, Hiroshima University, 5–8–1 Minato-machi, Takehara, Hiroshima, 725–0024, Japan. E-mail: ykondo@hiroshima-u.ac.jp (Kondo)
³Universiti Sultan Zainal Abidin, Gong Badak Campus, 21300 Kuala Terengganu, Terengganu, Malaysia
⁴Graduate School of Biosphere Science, Hiroshima University, 5–8–1 Minato-machi, Takehara, Hiroshima, 725–0024, Japan (formerly). E-mail: ionemadinabeitia@gmail.com (Madinabeitia)
⁵Ehime Prefecture Aquaculture Research Group Promotion Office of Agriculture, Forestry and Fisheries Research Institute, Fisheries Research Center, Uwajima, Ehime 798-0104, Japan. E-mail: yamashita-hirofumi@pref.ehime.lg.jp (Yamashita)
⁶Aquaculture Research Institute, Kindai University, 3153 Shirahama, Nishimuro, Wakayama, 649-2211, Japan. E-mail: shirakashi@kindai.ac.jp (Shirakashi)
⁷Meguro Parasititological Museum, 4-1-1 Shimomeguro, Meguro-ku, Tokyo 153-0064, Japan. E-mail: ogawak@kiseichu.org (Ogawa)
⁸Japan Fisheries Research and Education Agency, Fisheries Technology Institute, Kamiura, Saeki, Oita, 879-2602, Japan

(Received 4 August 2023 / Accepted 23 April 2025 / Published -- 2025)
Communicated by Benny K.K. Chan

The present study describes and illustrates the morphology of naupliar and copepodid stages of Caligus sclerotinosus Roubal, Armitage and Rohde, 1983 (Copepoda: Siphonostomatoida: Caligoida), an invasive, non-indigenous parasite collected from commercially important red sea bream Pagrus major (Temminck and Schlegel, 1843) (Sparidae) cultured as well as wild populations in western Japan. The life cycle of C. sclerotinosus consists of 8 stages: two nauplii, five copepodids (copepodid I to V) and one adult, which exhibited the general pattern of other congeners. Sexual dimorphism was first observed in the urosome and antenna of copepodid IV. The body lengths of the developmental stages of 14 Caligus spp. are compared to those of C. sclerotinosus. The oral cone of copepodid I is highly unique for its sucker-like shape, widely expanded terminally. All post-naupliar stages were found on the same host fish P. major, rejecting the previous hypothesis for the presence of intermediate hosts for the development of C. sclerotinosus.

Keywords: Aquaculture, Caligus sclerotinosus, Intermediate host, Japan, Life cycle, Non-indigenous, Pagrus major

Citation: Nishida Y, Aneesh PT, Kondo Y, Madinabeitia I, Yamashita H, Shirakashi S, Ogawa K, Wakabayashi K, Adachi K, Ohtsuka S. 2025. Developmental stages of an invasive, non-indigenous sea louce Caligus sclerotinosus Roubal, Armitage and Rhode, 1983 (Copepoda: Siphonostomatoida: Caligidae) parasitic on red sea bream Pagrus major (Temminck and Schlegel, 1843) collected from Japanese waters. Zool Stud 64:25.