Caligus epidemicus Hewitt, 1971

Boxshall, Geoff, 2018, The sea lice (Copepoda: Caligidae) of Moreton Bay (Queensland, Australia), with descriptions of thirteen new species, Zootaxa 4398 (1), pp. 1-172 : 62-66

Caligus epidemicus Hewitt, 1971

( Fig. 28 )

Material examined. 1♀ from Acanthopagrus australis (Günther, 1859) (TC17129) 14 January 2016, QM Reg. No. W53068; 2♀♀, 1♂ (TC 17862) 4 July 2016, QM Reg. No. W53069; 5♀♀, 2♂♂ (TC17855) 4 July 2016, QM Reg. No. W53070; 2♀♀ immatures (TC 17176) 15 January 2016, 1♀ (TC17489); 5♀♀ (TC17544) 24 June 2016, 1♀ (TC 17562) 24 June 2016, 2♂♂ (TC 17786) 1 July 2016, 2♀♀ (TC17814) 3 July 2016, 1♀, 1♀ immature (TC17816–17822) 3 July 2016, 3♀♀ (TC17822) 3 July 2016, 2♀♀ (TC17829) 3 July 2016, 3♀♀, 1♂ (TC17849) 4 July 2016, NHMUK Reg. Nos 2017. 418–427. 1♂ from Abudefduf vaigiensis (Quoy & Gaimard, 1825) (TC17091) 13 January 2016, NHMUK 2017.428; 1♀ immature, 1♂ from Acanthurus sp. ; 5♀♀, 1♂ from Gerres sp. (juveniles), 26 June 2016, NHMUK 2017.429–434; 7♀♀ from Girella tricuspidata (Quoy & Gaimard, 1824) (TC17803) 2 July 2016, NHMUK 2017.435–441; 1♂ immature (TC17744) 29 June 2016; 1♂ from Kyphosus bigibbus Lacepède, 1801 (TC17792) 1 July 2016, 1♂ (TC17864) 4 July 2016, NHMUK 2017.442–443; 2♀♀ from Kyphosus cinerascens (Forsskål, 1775) (TC17922) 5 July 2016, NHMUK 2017.444–445; 4♀♀ from Lagocephalus lunaris (Bloch & Schneider, 1801) (TC 17899) 5 July 2016, QM Reg. No. W53071; 1♂, 1 chalimus from Liza subviridis (Valenciennes, 1836) (TC17797) 4 July 2016, NHMUK 2017.446; 1♀ from Lutjanus fulviflamma (Forsskål, 1775) (TC17567) 24 June 2016, NHMUK 2017.447; 1♀ from Mugil cephalus Linnaeus, 1758 (TC17734) 29 June 2016, 3♀♀ (TC17856) 4 July 2016, NHMUK 2017.448–451; 1♀, 1 chalimus from Chrysophrys auratus (Forster, 1801) (TC17575) 25 June 2016; 1 ♀ immature from Pomatomus saltatrix (Linnaeus, 1766) (TC 17549) 24 June 2016; 1♂ from Saurida undosquamis (Richardson, 1848) (TC17854) 4 July 2016; 1♂ from Sillago analis Whitely, 1943 (TC16816), NHMUK 2017.452.

Site on host. Body surface.

Differential diagnosis. Cephalothorax extremely dorso-ventrally flattened, giving translucent appearance, and with distinctive square-ish outline ( Fig. 28A ). Marginal membranes on lateral zones of dorsal cephalothoracic shield well-developed. Frontal plates with lunules. Genital complex short, about 1.6 to 1.7 times wider than long; abdomen small, 1-segmented, wider than long; genital complex about 3.5 times longer than abdomen. Antenna with broad posterior process on proximal segment ( Fig. 28B ). Post-antennal process short and blunt ( Fig. 28B ); associated papillae unisensillate. Posterior process of maxillule simple; post-oral process present ( Fig. 28B ). Maxilliped of female slender, with smooth myxal margin. Sternal furca short, with short parallel tines ( Fig. 28C ). Distal exopodal segment of leg 1 with 3 plumose setae on posterior margin; distal spine 1 about as long as spines 2 and 3; spines 2 and 3 each with accessory process; seta 4 shorter than spine 3. Leg 2 with marginal setules on ……continued on the next page endopodal segments 1, 2 and 3; outer spines on exopodal segments 1 and 2 aligned close to longitudinal axis of ramus. Leg 3 without distinctive ornamentation on apron: exopod indistinctly 2-segmented ( Fig. 28D ); first exopodal segment with outer marginal flange plus short, slightly curved outer spine, without inner seta; compound distal segment subdivided by partial suture, armed with total of 4 outer spines and 5 plumose setae. Leg 4 uniramous, 3-segmented ( Fig. 28E ); first exopodal segment with long outer spine, second with apical spine longer than ramus plus subapical spine about one-third length of apical spine. Mean body length of female 2.51 mm, range 2.39 to 2.67 mm (based on 10 specimens).

Male ( Fig. 28F ) with similarly shaped and extremely flattened cephalothorax, as in female. Genital complex produced into large, triangular posterior lobes either side of short, 1-segmented abdomen. Leg 5 located laterally anterior to lobe and leg 6 located medial to lobe ( Fig. 28G ). Maxilliped with small spinous process on myxal surface. Mean body length of male 1.63 mm, range 1.56 to 1.75 mm (based on 9 specimens).

Remarks. Caligus epidemicus was first described from the lower Mitchell River in Victoria ( Australia) by Hewitt (1971) based on material from a sparid host, Acanthopagrus butcheri (Munro, 1949) (as Mylio butcheri ), and four mugilids, Mugil cephalus , Aldrichetta forsteri (Valenciennes, 1836) (as Alorichetta forsteri ), Liza argentea (Quoy & Gaimard, 1825) and Myxus elongatus Günther, 1861 . Roubal (1981) reported C. epidemicus from Acanthopagrus australis caught at Coffs Harbour (NSW). Subsequent parasitological surveys of four species of the genus Acanthopagrus Peters by Byrnes (1987) revealed the presence of C. epidemicus along the coast of every state of mainland Australia (not in Tasmania). It was discovered in Thailand on cultured decapods (giant tiger prawns) in 1977 ( Ruangpan & Kabata, 1984). This species has since been reported from numerous localities across the Indo-Pacific region including Taiwan (Lin, 1996) and the Philippines (Ho et al., 2004b). Its life cycle was elucidated by Lin et al. (1996b).

Caligus epidemicus exhibits a low level of host specificity and has previously been reported from at least 13 different families of fishes ( Table 4). As well as occurring on wild fishes, C. epidemicus occurs widely in finfish aquaculture systems: for example, Ho & Lin (2004) reported it from nine different host species cultured at three different localities around Taiwan (see Table 4), and it has even been recorded infesting the cultured decapod Penaeus monodon Fabricius, 1798 in Thailand ( Ruangpan & Kabata, 1984). It occurred at high prevalence rates and at high intensity on this very unusual host. Ho et al. (2004b) reported it from ten different host fish species in the Philippines and Venmathi Maran et al. (2009) recorded it from marine fish cultured in floating cage systems ( Table 4). Roubal (in Hallet & Roubal, 1995) reported high population levels on captive Acanthopagrus australis in Australia.

In the Moreton Bay survey, C. epidemicus was collected from 14 host species, of which 12 are new host records and this adds an additional seven host families to Table 4. It was never very common and often individuals were not adult, but the extreme flattening and the characteristic square shape of the cephalothorax are evident in the later developmental stages of this species, allowing them to be positively identified.

In its original description, C. epidemicus was reported as abundant in plankton samples taken in the brackish waters (salinity 4.5 to 28 ppt) of the lower reaches of the Mitchell River (Hewitt, 1971). Ho & Lin (2004) confirmed its tolerance to low salinities when they recorded C. epidemicus infestations that resulted in mortality among cultured host fishes in brackish water ponds in southern Taiwan. Similarly, C. epidemicus has been recorded on tilapia species ( Oreochromis spp.) in brackish water culture facilities at multiple sites across the Philippines ( Natividad et al., 1986).

Figures

FIGURE 28. Caligus epidemicus Hewitt, 1971, female. A, habitus, dorsal; B, antenna, post-antennal process and maxillule drawn in situ; C, sternal furca; D, exopod of leg 3; E, leg 4. Male, F, habitus, dorsal; G, left fifth and sixth legs, and caudal ramus, ventral view.Scale bars: 1.0 mm on A, F, 200 µm on B, E, G, 100 µm on D, 50 µm on C.