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      Discovery of the fish host of the ‘planktonic’ caligid Caligus undulatus Shen & Li, 1959 (Crustacea: Copepoda: Siphonostomatoida)

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          Abstract

          The siphonostomatoid copepod Caligus undulatus Shen & Li, 1959 has been widely reported from plankton samples obtained from neritic and oceanic waters off coasts of the Indo-West Pacific and Atlantic Oceans. Until now, its fish host has remained unknown. This copepod belongs to an intriguing group of congeners that, despite being part of a chiefly parasitic group, are consistently found as zooplankters. Quite unexpectedly, in October 2019, a fish host of C. undulatus was discovered in the Seto Inland Sea, Japan—namely, the Japanese sardinella Sardinella zunasi (Bleeker, 1854). Both juvenile (chalimus) and adult individuals of this caligid were observed as parasites of the fish host. The discovery suggests that the species has an alternative life cycle as previously proposed for other purportedly ‘planktonic’ congeners and might frequently switch hosts during the adult stage. Thus, the C. undulatus group is newly proposed as a species group in the genus, in which five species are known as planktonic. Some hypotheses on the modified life cycle of caligids also briefly discussed.

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          The global economic cost of sea lice to the salmonid farming industry.

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            Ecology of sea lice parasitic on farmed and wild fish.

            Sea lice, especially Lepeophtheirus salmonis and Caligus spp., have the greatest economic impact of any parasite in salmonid fish farming and are also a threat to wild salmonids. Here, I review how the biology and ecology of various louse and host species influence their pathogenicity and epidemiology. Recent discoveries of new species and genotypes emphasize the need for more basic research on louse taxonomy and host preferences. Louse development rates are strongly dependent on temperature, and increasing mean sea temperatures are likely to increase infestation pressure on farms and wild fish, as well as affecting the geographical distribution of hosts and parasites. Despite progress in finding L. salmonis larvae in the plankton and in modelling louse production in several countries, more data on larval behaviour and distribution are required to develop dispersal and transmission models for both L. salmonis and Caligus spp. This knowledge could be used to take measures to reduce the risks of lice affecting farmed and wild fish.
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              The Salmon Louse Lepeophtheirus salmonis (Copepoda: Caligidae) Life Cycle Has Only Two Chalimus Stages

              Each year the salmon louse ( Lepeophtheirus salmonis Krøyer, 1838) causes multi-million dollar commercial losses to the salmon farming industry world-wide, and strict lice control regimes have been put in place to reduce the release of salmon louse larvae from aquaculture facilities into the environment. For half a century, the Lepeophtheirus life cycle has been regarded as the only copepod life cycle including 8 post-nauplius instars as confirmed in four different species, including L . salmonis . Here we prove that the accepted life cycle of the salmon louse is wrong. By observations of chalimus larvae molting in incubators and by morphometric cluster analysis, we show that there are only two chalimus instars: chalimus 1 (comprising the former chalimus I and II stages which are not separated by a molt) and chalimus 2 (the former chalimus III and IV stages which are not separated by a molt). Consequently the salmon louse life cycle has only six post-nauplius instars, as in other genera of caligid sea lice and copepods in general. These findings are of fundamental importance in experimental studies as well as for interpretation of salmon louse biology and for control and management of this economically important parasite.
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                Author and article information

                Contributors
                Journal
                Biodivers Data J
                Biodivers Data J
                1
                urn:lsid:arphahub.com:pub:F9B2E808-C883-5F47-B276-6D62129E4FF4
                urn:lsid:zoobank.org:pub:245B00E9-BFE5-4B4F-B76E-15C30BA74C02
                Biodiversity Data Journal
                Pensoft Publishers
                1314-2836
                1314-2828
                2020
                08 June 2020
                : 8
                : e52271
                Affiliations
                [1 ] Fisheries Science Laboratory, Setouchi Field Science Center, Graduate School of Integrated Sciences for Life, Hiroshima University, Takehara, Japan Fisheries Science Laboratory, Setouchi Field Science Center, Graduate School of Integrated Sciences for Life, Hiroshima University Takehara Japan
                [2 ] Fisheries Science Laboratory, Setouchi Field Science Center, School of Applied Biological Science, Hiroshima University, Takehara, Japan Fisheries Science Laboratory, Setouchi Field Science Center, School of Applied Biological Science, Hiroshima University Takehara Japan
                [3 ] Graduate School of Science, Kobe University, Kobe, Japan Graduate School of Science, Kobe University Kobe Japan
                [4 ] Endangered Marine Species Research Unit, Borneo Marine Research Institute, Universiti Malaysia Sabah, Kota Kinabalu, Malaysia Endangered Marine Species Research Unit, Borneo Marine Research Institute, Universiti Malaysia Sabah Kota Kinabalu Malaysia
                [5 ] El Colegio de la Frontera Sur (ECOSUR), Unidad Chetumal, Chetumal, Mexico El Colegio de la Frontera Sur (ECOSUR), Unidad Chetumal Chetumal Mexico
                Author notes
                Corresponding author: Masato Nitta ( licht.bsn.mono@ 123456gmail.com ).

                Academic editor: Yasen Mutafchiev

                Author information
                https://orcid.org/0000-0001-6018-7442
                https://orcid.org/0000-0003-3063-6029
                https://orcid.org/0000-0003-1090-5295
                Article
                52271 13464
                10.3897/BDJ.8.e52271
                7295818
                ab3b9e3d-32f0-469f-8ba7-4a6940561577
                Susumu Ohtsuka, Masaki Nawata, Yusuke Nishida, Masato Nitta, Katsushi Hirano, Kenta Adachi, Yusuke Kondo, Balu Alagar Venmathi Maran, Eduardo Suárez-Morales

                This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 20 March 2020
                : 27 May 2020
                Page count
                Figures: 1, Tables: 0, References: 58
                Categories
                Short Communication

                antagonism,caligus undulatus,life cycle,plankton,sardinella zunasi

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