Toxicon 48 (2006) 116–122 Accumulation of tetrodotoxin (TTX) in Pseudocaligus fugu, a parasitic copepod from panther puffer Takifugu pardalis, but without vertical transmission—Using an immunoenzymatic technique Koichi Ikeda a , B.A Venmathi Maran b,Ã , Shunichi Honda a , Susumu Ohtsuka b , Osamu Arakawa c , Tomohiro Takatani c , Manabu Asakawa d , Geoffrey A. Boxshall e a Graduate School of Science and Technology, Nagasaki University, Nagasaki 852-8521, Japan b Takehara Marine Station, Setouchi Field Science Center, Graduate School of Biosphere Science, Hiroshima University, 5-8-1 Minato-machi, Takehara 725-0024, Japan c Faculty of Fisheries, Nagasaki University, Nagasaki 852-8521, Japan d Graduate School of Biosphere Science, Hiroshima University, Higashi Hiroshima, Hiroshima 739-8528, Japan e Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK Received 9 January 2006; accepted 27 April 2006 Available online 12 May 2006 Abstract The caligid copepod Pseudocaligus fugu, a common parasite on the body surface of both toxic (Takifugu pardalis) and cultured, non-toxic (Takifugu rubripes) puffer fishes, was isolated and analyzed for the presence of tetrodotoxin (TTX) using a monoclonal anti-TTX antibody-based immunohistochemical technique. Histological sections of female P. fugu from Takifugu pardalis explicitly revealed that positive brown staining was visible in regions of gut and appendages, and also in the general body tissues from the prosome to the urosome. It is absent from the epicuticle, ovary, oviduct, uterus and egg sacs, where clear negative blue color reaction was obtained. In contrast, the caligids on cultured, non-toxic Takifugu rubripes, considered as negative control, had no sign of TTX. The results indicate that there is no vertical transmission of TTX in the parasitic caligids, which could acquire TTX by feeding on the toxic mucus and skin tissues of host puffer fish. r 2006 Elsevier Ltd. All rights reserved. Keywords: Pseudocaligus fugu; Toxic and non-toxic puffer fishes; Tetrodotoxin; Monoclonal antibody; Vertical transmission 1. Introduction Parasitic copepods are common on cultured and wild marine finfish (Ho and Lin, 2004). Members of the family Caligidae (Siphonostomatoida), sea lice are the most commonly reported copepod species on marine and brackish water cultured fish throughout the world, and cause serious problems in salmonid culture in Europe and North America (Boxshall and Defaye, 1993; Nagasawa, 2004). The caligid Pseudocaligus fugu (Fig. 1) is parasitic on both wild and cultured marine puffer fishes in Japan ARTICLE IN PRESS www.elsevier.com/locate/toxicon 0041-0101/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.toxicon.2006.04.019 Ã Corresponding author. Tel.: +81 846 22 2362; fax: +81 846 23 0038. E-mail address: venmathi@hiroshima-u.ac.jp (B.A. Venmathi Maran).