Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aquaculture Review Rhizocephalans and their potential impact on crustacean aquaculture Khor Waiho a,b, ⁎ , Henrik Glenner c,d , Aleksei Miroliubov e , Christoph Noever c , Marina Hassan a,b , Mhd Ikhwanuddin a,b , Hanafiah Fazhan a,b,f, ⁎ a Institute of Tropical Aquaculture and Fisheries, Universiti Malaysia Terengganu, Terengganu, Malaysia b STU-UMT Joint Shellfish Research Laboratory, Shantou University, Shantou, China c Department of Biological Sciences, University of Bergen, Bergen, Norway d Center for Macroecology and Evolution, University of Copenhagen, Copenhagen, Denmark e Laboratory of Parasitic Worms and Protists, Zoological Institute of the Russian Academy of Sciences, Saint-Petersburg, Russia f Guangdong Provincial Key Laboratory of Marine Biotechnology, Shantou University, Guangdong 515063, China ARTICLEINFO Keywords: Rhizocephalan Crustacean aquaculture Parasitic barnacles Parasite Feminization Anecdysis ABSTRACT Crustaceans play essential roles as food sources for global coastal communities, and their fisheries and aqua- culture support the economic growth of many coastal countries. Thus, the understanding of diseases in crus- taceans,especiallythosewithhigheconomicvalues,areimportantfortheircureandprevention.Amongother parasitesthatparasitisecrustaceans,parasiticbarnacles(Rhizocephala)areconsideredthemostintriguing,both in terms of their unique life cycle and the detrimental changes they induced upon their hosts such as host sterilisation, moult inhibition (anecdysis), growth reduction, feminisation of male individuals, and behaviour alteration.Inadditiontodiscussingindetailthemorphological,physiologicalandbehaviouralchangescaused by rhizocephalan infestations, this review also shows that rhizocephalans are found in most economically im- portant crustacean species around the world. Based on their reported adverse effects on their hosts, their po- tential implications on various aspects of crustacean aquaculture including broodstock selection, culture and fattening, soft-shell crab production and breeding programs are discussed. Although treatment or cure for rhi- zocephalan infestation has yet to be found, several recommendations are provided to enable accurate identifi- cationandhandlingofinfectedhostsandexposedaquaculturefacilitiesinordertominimizelossesandprevent parasite outbreaks. 1. Introduction Rhizocephalan parasites (Crustacea, Cirripedia) or parasitic barna- cles infect other crustacean species and cause remarkable morpholo- gical, physiological and behavioural changes (Veillet, 1945).Theyare considered as among the most highly specialized and extremely di- vergent forms of parasites in the animal kingdom (Delage, 1884; Kobayashietal.,2018)astheadultparasiteislackingalmostalltypical crustacean characters (e.g. lack of segmentation and appendages) and onlypossessaroot-likenetwork(interna)fornutrientabsorptionwhich spreads throughout the host’s body (Noever et al., 2016b; Miroliubov etal.,2019)andanunsegmentedsac-likereproductiveorgan(externa), which is visibly protruding from the host (Walker, 2001; Glenner and Hebsgaard, 2006). In fact, it is the morphological characteristics of its larvae that originally disclosed rhizocephalans as Crustacea within Cirripedia (Thompson, 1836). However, unlike larvae of other barna- cles, rhizocephalan larvae possess advanced and highly effective mechanismstoinfecttheircrustaceanhosts(Gould,1996).Theexterna releases planktonic larvae, of which only the female larvae are re- sponsible for host infection (Yanagimachi, 1961; Walker, 1987). The female, upon developing a juvenile externa has to attract the male larvae, which enter the female externa where they embed themselves andfertilizetheeggs(Høeg, 1987). Typical adverse effects of rhizocephalan infection may include feminisation of external secondary sexual characters, reduction of pri- mary sexual characters (Kristensen et al., 2012; Waiho et al., 2017b), gonadal degeneration (Mouritsen et al., 2018), behavioural changes (Rasmussen, 1959; Mouritsen and Jensen, 2006; Belgrad and Griffen, 2015),inhibitionofmoulting(TakahashiandMatsuura,1994),alower fitness and increased mortality (Larsenetal.,2013). The hosts of rhizocephalans include various crabs (Isaeva et al., 2005; Waihoetal.,2017b; Fazhanetal.,2018; Kobayashietal.,2018), shrimps (Høeg, 1982; Lützen and Du, 1999; Noever et al., 2016a; Nagler et al., 2017), prawns (Lützen, 1981) and lobsters (Boyko and https://doi.org/10.1016/j.aquaculture.2020.735876 Received11April2020;Receivedinrevisedform17August2020;Accepted22August2020 ⁎ Corresponding authors at: Institute of Tropical Aquaculture and Fisheries, Universiti Malaysia, Terengganu 21030, Terengganu, Malaysia. E-mail addresses: waiho@umt.edu.my (K. Waiho), fazhanhanafiah@gmail.com (H. Fazhan). Aquaculture 531 (2021) 735876 Available online 25 August 2020 0044-8486/ © 2020 Elsevier B.V. All rights reserved. T