Argulus elongatus (Branchiura, Argulidae) in fish in the upper São Francisco river, Brazil

rayaneduarte20394@hotmail.com Abstract Among 164 fish from the upper São Francisco river, caught in the Três Marias reservoir (18º 12’ 59” S; 45º 17’ 34” W) or downstream from this reservoir (18º 12’ 32” S; 45º 15’ 41” W) in 2007, 2008, 2016 and 2017, four specimens of Argulus elongatus Heller, 1857 were found, one specimen per fish, in the following host species: Brycon orthotaenia Günther (two fish parasitized out of 38 examined) and Salminus hilarii Valenciennes (one fish parasitized out of 45 examined) (both in Bryconidae); and Metynnis lippincottianus (Cope) (one fish parasitized out of 81 examined) (Serrasalmidae). This opportunistic ectoparasite deserves attention even in the case of low infestation in fish in a natural water system. This is the first record of a branchiuran species in B . orthotaenia ; the host list of A . elongatus is extended through addition of the three fish species examined in this study, and the known Brazilian geographical distribution of this argulid is enlarged to the São Francisco river

Branchiura is a group of crustaceans that usually parasitizes both freshwater and saltwater fish and is recognized by fishermen and fish farmers as 'fish lice' (Lemos de Castro, 1985;Thatcher, 2006). They parasitize the surface of the body, fins, buccal cavity and gills of fish and can occasionally parasitize amphibians, reptiles and some invertebrates (Ringuelet, 1943;Poly, 2008). Argulidae is the only family in Branchiura and it comprises four genera: Argulus Müller, 1785, Chonopeltis Thiele, 1900, Dipteropeltis Calman, 1912, and Dolops Audouin, 1837. This family has the highest diversity of genera and species occurring in the Afrotropical and Neotropical regions, in comparison with other biogeographical areas of the world: Nearctic, Oriental, Palearctic, Australasia with Pacific Ocean islands and Antarctica (Poly, 2008).
Reports of injuries to fish caused by argulids have included blood and tissue consumption at the puncture site; fungal infections at the puncture site; and transmission of viral and bacterial diseases (Thatcher, 2006;Poly, 2008;Woo & Buchmann, 2012). These reports highlight the importance of reporting occurrences of these ectoparasites, even when they are uncommon in the fish communities of natural water systems.
In 2007, 2008, 2016 and 2017, a total of 164 fish specimens were caught by artisanal fishermen in the upper São Francisco river, state of Minas Gerais, Brazil. Among these, 139 fish were caught in the Três Marias reservoir (18º 12' 59" S; 45º 17' 34" W), consisting of 13 specimens of B. orthotaenia Günther, 1864Günther, (in 2008 (1985) and Thatcher (2006); and the argulid species were identified in accordance with Thiele (1904). The ectoparasite specimens were mounted on temporary slides using Amann's lactophenol for morphological evaluation and to make photomicrographs using an Olympus BX41 light microscope. Voucher specimens of the parasitic argulids were deposited in liquid medium (70 ºGL ethanol) in the Crustacea Collection of the National Institute for Amazon Research (Instituto Nacional de Pesquisas da Amazônia; INPA): 2501 (B. orthotaenia), 2503 (S. hilarii) and 2502 (M. lippincottianus). The ecological parameters of prevalence (P), mean intensity (MI) and mean abundance (MA) were determined as described by Bush et al. (1997). Argulus elongatus is considered to be a generalist parasite, and was recorded with low prevalence in the three host species in the current study. Nonspecificity is inherent among argulid species. Hence, specimens of a particular species can be found in several species of fishes and, conversely, a single fish can be parasitized by different species of argulids. In addition, these branchiurans can easily move from one point to another on the host, and they are able to swim swiftly through the thoracic appendages. These characteristics help in understanding the diversity of fish species that they can parasitize (Lemos de Castro, 1985).
This opportunistic ectoparasite deserves attention because it can cause several types of injury to its hosts through spoliation and trauma in the tissues. The severity of injuries depends on the intensity of infestation, such that numerous lesions are often sites that allow secondary infections. These parasites can have a serious impact on farmed fish, mainly because these fish are concentrated in small areas or held under semi-confinement, but may also affect fish from natural water systems (Kabata, 1970;Thatcher, 2006;Poly, 2008).
Among the hosts analyzed in the present study, S. hilarii and M. lippincottianus are known to have geographical distribution outside of the São Francisco river (Shibatta & Garavello, 1993;Sato & Sampaio, 2006). Salminus hilarii was recorded as a host in Brazil for Argulus paulensis Wilson, 1924, according to Thatcher (2006; while M. lippincottianus in the Igarapé Fortaleza basin, a tributary of the Amazon river, in Macapá, state of Amapá, was recorded as a host for the argulid Dolops longicauda Heller, 1857 (Hoshino & Tavares-Dias, 2014).
Argulus elongatus was described by Heller in 1857 from a female specimen that was very poorly preserved in the zoological collection of the Natural History Museum of Vienna (Naturhistorischen Museum Wiener), in Austria (Thiele, 1904), which originated from an unidentified host in Brazil (Thiele, 1904;Moreira, 1913). This type specimen was reexamined and illustrated (Thiele, 1904). In Brazil, A. elongatus among other branchiurans species, was recorded in Pygocentrus nattereri Kner, 1858, Serrasalmus marginatus Valenciennes, 1837, and Serrasalmus spilopleura Kner, 1858. These are all serrasalmid fish living in the Miranda river basin of the Pantanal wetland, state of Mato Grosso do Sul (Carvalho et al., 2003). Recently, A. elongatus was recorded in Leporinus fasciatus (Bloch, 1794) [Anostomidae] and P. nattereri from the Matapi River, state of Amapá (Neves & Tavares-Dias, 2019). Now, through the present study, one endemic species, B. orthotaenia, and one nonendemic species, S. hilarii (both in Bryconidae), and one introduced fish species, M. lippincottianus (Serrasalmidae), are also added as known hosts for A. elongatus in the São Francisco river basin. It is noteworthy that, over the years, not as many records of A. elongatus have been published as have been for its congeners. Therefore, a more detailed description of this ectoparasite is required, considering its hosts and its geographical distribution. As contributions to this, the present study adds three species of fish to the host list of A. elongatus, and the São Francisco river basin is added to the known geographical distribution of this ectoparasite species in Brazil.