Introduction

Materials and methods

Taxon treatment

Caligus dussumieri Rangnekar, 1957

Nomenclature

Sinocaligus dussumieri (Rangnekar, 1957)

Pseudopetalus dussumieri (Rangnekar, 1957)

Caligus rivulatus (Pilla, Vankara and Chikkam, 2012)

Materials   Download as CSV 

1. scientificName:
   Caligus dussumieri Rangnekar, 1957
   ; originalNameUsage:
   Caligus dussumieri Rangnekar, 1957
   ; taxonomicStatus:
   Accepted
   ; taxonID:
   349612 (urn:lsid:marinespecies.org:taxname:349612)
   ; parentNameUsage:
   Caligus Müller O.F., 1785
   ; kingdom:
   Animalia
   ; phylum:
   Arthropoda
   ; class:
   Copepoda
   ; order:
   Siphonostomatoida
   ; family:
   Caligidae
   ; genus:
   Caligus
   ; specificEpithet:
   dussumieri
   ; scientificNameAuthorship:
   Rangnekar, 1957
   ; higherGeography:
   South East Asia
   ; continent:
   Asia
   ; waterBody:
   South China Sea
   ; country:
   Malaysia
   ; stateProvince:
   Terengganu
   ; county:
   Kuala Terengganu
   ; verbatimLocality:
   LKIM Pulau Kambing
   ; verbatimCoordinates:
   5°19'N 103°7' 43.7"E
   ; verbatimLatitude:
   5.321971
   ; verbatimLongitude:
   103.1288
   ; samplingProtocol:
   Gill wash
   ; year:
   2019
   ; month:
   10
   ; day:
   19
   ; identificationID:
   urn:lsid:marinespecies.org:taxname:349612
   ; occurrenceID:
   A71C4FDE-7825-5C4B-9023-C44E1AC10847
2. scientificName:
   Caligus dussumieri Rangnekar, 1957
   ; originalNameUsage:
   Caligus dussumieri Rangnekar, 1957
   ; taxonomicStatus:
   Accepted
   ; taxonID:
   349612 (urn:lsid:marinespecies.org:taxname:349612)
   ; parentNameUsage:
   Caligus Müller O.F., 1785
   ; kingdom:
   Animalia
   ; phylum:
   Arthropoda
   ; class:
   Copepoda
   ; order:
   Siphonostomatoida
   ; family:
   Caligidae
   ; genus:
   Caligus
   ; specificEpithet:
   dussumieri
   ; scientificNameAuthorship:
   Rangnekar, 1957
   ; higherGeography:
   Australia
   ; continent:
   Australia
   ; country:
   Australia
   ; county:
   Camden Sound
   ; locality:
   Western Australia
   ; verbatimCoordinates:
   16° 11.52’S 124° 32.52’E
   ; year:
   2013
   ; month:
   9
   ; day:
   11
   ; identificationID:
   urn:lsid:marinespecies.org:taxname:349612
   ; institutionCode:
   NHMUK
   ; collectionCode:
   Reg. Nos. 2022.189-197
   ; occurrenceID:
   ADE72616-49DB-57BB-89BA-3948143646FA

Description

Fig. 1

Figure 1.  

Caligus dussumieri Rangnekar, 1957, adult female.

A Habitus, dorsal view; B Antennule; C Antenna; D Mandible; E Maxilla; F Maxilliped; G Sternal furca.

Female. Body (Fig. 1A) 3.24 mm long, excluding setae on caudal ramus. Dorsal cephalothoracic shield subcircular, slightly longer than wide. 1.31 x 1.12 mm, excluding hyaline membrane along lateral margins. Shield tapering anteriorly; with large, conspicuous lunules. Fourth pediger wider than long, incompletely fused to genital complex. Genital complex about 1.96 times longer than wide with neck-like narrow part anteriorly and barrel-shaped posterior region. Leg 5 (Fig. 1A) represented by 1 plumose, outer protopodal seta and 2 plumose setae on exopodal papilla located on posterolateral margin of genital complex. Abdomen 1-segmented, about 2.8 times longer than wide. Caudal ramus (Fig. 2C) oval, 0.10 x 0.07 mm, expanded inwards distally; armed with 3 short and 3 long plumose setae and ornamented with row of setules along distomedial margin.

Figure 2.  

CLSM images of Caligus dussumieri Rangnekar, 1957.

A Exopod of leg 1, showing spinular ornamentation on plumose setae along posterior margin; B Rami of leg 2 showing ornamentation on outer margin of endopod and spatulate spine on first exopodal segment.

Australian female observed using CLSM (Fig. 3A, B) showing differential degree of staining over body surface. Dorsal cephalothoracic shield staining moderately and evenly, with heavier uptake of stain marking sutures anteriorly near origin of antennules, in area near eyes and along lateral edges of central thoracic zone of shield. Ventral curved rib marking boundary of cephalosome and incorporated first pediger strongly stained. Fourth pediger and fourth leg staining evenly. Genital complex and abdomen displaying marked differences in intensity of staining. Staining intense in small ovoid patch on dorsal surface of genital complex towards the posterior end, ventrally around the genital apertures and in the posterior part of the abdomen. Conversely, staining very light in other areas of genital complex and anterior part of abdomen.

Figure 3.  

CLSM images of Caligus dussumieri Rangnekar, 1957.

A dorsal view; B ventral view.

Antennule (Fig. 1B) 2-segmented; proximal segment carrying 27 plumose setae on anterodistal surface, 25 setose plus 2 naked (on dorsal side) setae; distal segment short with 1 subterminal seta on posterior margin and 11 setae plus 2 aesthetascs around apex. Antenna (Fig. 1C) 3-segmented; proximal segment smallest, with short blunt process on posteromedial corner; middle segment subrectangular, unarmed; distal segment forming long, curved claw armed with stout proximal seta and simple middle seta. Postantennal process (Fig. 1C) shorter than distal segment, tine curved inwards with blunt tip, ornamented with 2 multisensillate papillae on basal region and another multisensillate papillae present on sternum adjacent to base of process. Additional lobate process present between postantennal process and base of antenna. Mandible (Fig. 1D) stylet-like, with 4 sections, bearing 12 teeth on medial margin of distal blade. Maxillule (Fig. 1C) comprising large stout dentiform process and basal papilla with 3 setae (1 short, 1 medium and 1 long). Maxilla (Fig. 1E) 2-segmented; lacertus large and unarmed; slender distal segment (brachium) bearing rounded membranous subapical flabellum on anterior margin and terminating in 2 subequal claw-like elements (calamus and canna). Calamus longer than canna, ornamented with strips of serrated membrane arranged obliquely around surface; canna ornamented with strips of serrated membrane bilaterally. Maxilliped (Fig. 1F) 3-segmented; proximal segment (corpus) largest, unarmed, 2 unequal processes along myxal area, longer than next 2 segments combined (subchela); middle segment unarmed; distal claw longer than shaft, sharply pointed with long seta at base of claw. Sternal furca (Fig. 1G) subrectangular, box with tiny rounded outgrowth anteriorly, tines blunt and weakly divergent.

Leg 1 (Fig. 4A, Fig. 2A) with 2 segmented protopod bearing 1 inner and 1 outer small plumose seta plus bifid setule on outer margin. Intercoxal sclerite slender, with 2 papillae each bearing a setule present on sternum posterior to sclerite. Vestigial endopod reduced to tiny, pointed process located near base of exopod. Exopod 2-segmented, first segment with row of fine setules along inner margin and spiniform seta at outer distal corner; second segment with 3 large plumose setae ornamented along outer margin with stout spinules at base becoming finer towards tip and with short plumosities along inner margin; 4 terminal elements, spine 1 simple, spines 2 and 3 each with accessory process (Fig. 4a), seta 4 longest, stout and pinnate on only one side. Leg 2 (Fig. 4B, Fig. 2B) with intercoxal sclerite ornamented with marginal membrane along posterior margin; coxa with large plumose seta at posterior corner and minute setule on anterior surface; basis ornamented with marginal membrane on both inner and medial margins, bearing minute seta at outer distal corner plus setule near mid-point of inner margin. Endopod 3-segmented: first segment armed with inner plumose seta and ornamented with large denticles at outer distal corner; second segment with 2 inner distal setae plus row of robust denticles along outer margin; third segment with 6 plumose setae. Exopod 3-segmented: first segment with reflexed membrane dorsally and with pecten at base of long, stout, outer spine with spatulate tip extending obliquely across surface of second and third segments; second segment with relatively short outer spine, third segment armed with 1 small and 1 medium outer spine (latter ornamented with extensive marginal membrane), longer distal spine ornamented with membrane on outer side and plumosities on inner side, plus 5 plumose setae. Leg 3 (Fig. 5A) apron (protopod) bearing small, plumose outer seta and long, plumose inner seta and ornamented with membrane along outer and posterior margins, 4 patches of spinules plus 2 setule-bearing papillae on either side of innermost patch, plus 2 relatively long setules near posterior margin. Endopod 2-segmented, proximal segment small, armed with 1 long plumose seta; segment expanded to form velum fringed with setules along free margin; second segment armed with 6 plumose setae. Exopod 3-segmented, proximal segment small, with pecten-like membrane on inner margin of segment and with an expanded outer distal corner ornamented with strip of membrane located lateral to outer spine plus minute setule on outer margin, outer distal spine slightly curved, not reaching distal border of second segment (Fig. 5a); second segment with inner plumose seta and outer naked spine; third segment with 3 setiform spines increasing in size distally plus 4 inner setae. Leg 4 (Fig. 5B) plumose seta at outer distal corner of protopodal segment; exopod distinctly 2-segmented, first exopodal segment with long outer spine; second segment with 4 spines along oblique outer distal margin; each spine with pecten at base (Fig. 5b).

Figure 4.  

Caligus dussumieri Rangnekar, 1957 adult female.

A Leg 1, a Four terminal elements of Leg 1; B Leg 2.

Figure 5.  

Caligus dussumieri Rangnekar, 1957, adult female.

A Leg 3, a Proximal segment of leg 3 exopod; B Leg 4, b Distal elements of Leg 4 second segment.

Taxon discussion

The initial description of C. dussumieri was provided by Rangnekar (1957). It was later transferred by Pillai (1968) to his new genus Pseudopetalus Pillai, 1968, as Pseudopetalus dussumieri, but was subsequently transferred to Sinocaligus Shen 1957 as Sinocaligus dussumieri after Pseudopetalus was recognised as a junior synonym of Sinocaligus (Boxshall and Montu 1997, Dojiri and Ho 2013). In a recent comprehensive revision by Boxshall and Barton (2023), the complex taxonomic history of C. dussumieri was thoroughly examined. They proposed to recognise Sinocaligus as a junior subjective synonym of Caligus and returned S. dussumieri to its original combination as C. dussumieri. Boxshall and Barton (2023) also recognised Caligus rivulatus Pilla, Vankara and Chikkam, 2012, described from Lutjanus rivulatus Cuvier, 1828 in Indian waters, as a junior subjective synonym of C. dussumieri. The Malaysian specimen was identified as a mature pre-metamorphic female due to the presence of elongated and slender genital complex and abdomen, which corresponds closely with the developmental stage described in the previous studies by Pilla et al. (2012) and Boxshall and Barton (2023). This particular specimen measured 3.24 mm in total length, a measurement consistent with the total length range of C. dussumieri, referred to as C. rivulatus by Pilla et al. (2012), ranging from 2.36 to 3.12 mm. Similarly, it exhibited a comparable total length to the Australian specimens, which measured between 3.05 and 3.65 mm.

In comparison to the recent re-description of C. dussumieri from Australian waters as provided by Boxshall and Barton (2023), the C. dussumieri specimens from Malaysia displayed subtle differences including the presence of a neck-like constriction in the anterior part of the genital complex and the more barrel-shaped genital complex, features also observed in C. dussumieri from Indian waters (Rangnekar 1957, Pillai 1967, Pilla et al. 2012). As discussed below, we consider these differences can be explained by the pre-metamorphic stage of development of these sets of specimens.

Another minor difference was noted regarding the postantennal process. In the current study, C. dussumieri possessed trisensillate papillae, consistent with the description of Pillai (1985), while the Australian specimens exhibited bisensillate papillae. In addition, a rounded, lobate process was present between the postantennal process and the base of the antenna in the Malaysian female. The female from Malaysia lacked the patch of small setules at the base of the inner protopodal seta of leg 1, present in the other specimens. Furthermore, the tips of spines 2 and 3 on the distal exopodal segment of leg 1 were ornamented with a row of serrations, distinguishing them from previously described specimens from India and Australia.

A pecten-like structure at the outer distal corner of the first exopodal segment of leg 3 was observed in the present specimen, but this feature was not illustrated in previous studies. However, this structure's presence in the Australian material was subsequently confirmed through additional observations of Australian specimens in this study.

Identification keys

Analysis

Discussion

Host relationships

Caligus dussumieri has been observed to infect two distinct host families, the Lutjanidae and Dussumieriidae. The adult males, copepodid (including chalimus) stages and mated, but not fully metamorphosed adult females were found on Lutjanus johnii from Australian waters (Boxshall and Barton 2023) and L. rivulatus from Indian waters (Pilla et al. 2012). Our new Malaysian female at the same stage of development is from L. malabaricus. Fully matured females with the typical expanded genital complex and abdomen have been found on the dussumieriids Dussumieria acuta Valenciennes, 1847 and D. elopsoides Bleeker, 1849 (as D. hasseltii Bleeker) both in Indian waters (Rangnekar 1957, Pillai 1968).

Lutjanids are a group of fish with high commercial value due to their desirable taste, ability to reproduce in captivity and tolerance to a range of salinity regimes which allow them to thrive in various marine environments including estuaries and mangroves as well as the open sea (Ibarra-Castro and Duncan 2007). In the family Lutjanidae, Lutjanus is the most species rich genus, currently accommodating 73 species (Froese and Pauly 2023). Twenty-eight species of caligid copepods have been recorded so far from Lutjanus species. Amongst these are five species belonging to the bonito-group within Caligus, namely: C. asperimanus, C. bonito, C. irritans, C. mutabilis and C. tenuifurcatus (Table 1).

Table 1.

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XLSX

Caligid copepods recorded from the genus Lutjanus Bloch,1790.

Lutjanus fish host	Caligus species	Geographic distribution	References
Lutjanus analis (Cuvier, 1828)	Caligus asperimanus Pearse, 1951	Carrie Bow Cay, Belize	Cressey (1991)
	Caligus asperimanus Pearse, 1951	Bahamas	Cressey (1991)
	Caligus asperimanus Pearse, 1951	off the coast of Rio de Janeiro, Brazil.	Oliveira et al. (2020)
	Caligus robustus Bassett-Smith, 1898	Mexico	Cressey (1991)
Lutjanus apodus Walbaum, 1792	Caligus asperimanus Pearse, 1956	Carrie Bow Cay, Belize	Cressey (1991)
	Caligus atromaculatus Wilson, 1913	Venezuela	Lagarde (1991)
	Caligus tenax Heller, 1865	Venezuela	Lagarde (1991)
	Caligus robustus Bassett-Smith, 1898	Belize	Cressey (1991)
	Caligus xystercus Cressey, 1991	Belize	Cressey (1991)
Lutjanus argentimaculatus Forsskål, 1775	Caligus epidemicus Hewitt, 1972	Philipines	Ho et al. (2004)
	Caligus lutjani Ho, Lin and Chang, 2007	Taiwan	Ho et al. (2007)
	Caligus quadratus Shiino, 1954	Taiwan	Ho et al. (2007)
Lutjanus argentiventris Peters, 1869	Caligus asperimanus Pearse, 1961	Manabí Coast, Ecuador	Morales-Serna et al. (2016)
	Caligus diaphanus Nordmann, 1833	Jaramijó, Ecuador	Morales-Serna et al. (2015)
	Caligus latigenitalis Shiino, 1954	Bahía de Chamela, Mexican Pacific	Morales-Serna et al. (2014)
	Caligus latigenitalis Shiino, 1955	Jaramijó, Ecuador	Morales-Serna et al. (2015)
	Caligus serratus Shiino, 1965	Mexican Pacific	Morales-Serna et al. (2012), Morales-Serna et al. (2014)
	Caligus schistonyx Wilson, 1905	Jaramijó, Ecuador	Morales-Serna et al. (2015)
	Caligus tenuifurcatus Wilson, 1937	Mexican Pacific	Suarez-Morales et al. (2008), Morales-Serna et al. (2012), Morales-Serna et al. (2015)
Lutjanus bohar Forsskål, 1775	Caligus lutjani	Taiwan	Ho et al. (2007)
Lutjanus colorado Jordan and Gilbert, 1882	Caligus sclerotinosus Roubal, Armitage and Rohde, 1983	Bahía de Chamela,Mexican Pacific	Morales-Serna et al. (2014)
Lutjanus erythropterus Bloch, 1790	Caligus chiastos	Malaysia	Muhd-Faizul et al. (2012)
	Caligus clemensi	Penang, Malaysia	Yahaya et al. (2022)
	Caligus torpedinis (as C. rotundigenitalis)	Malaysia	Venmathi Maran et al. (2009)
Lutjanus fulviflamma Forsskål, 1775	Caligus chiastos	Taiwan	Ho and Lin (2004)
	Caligus chiastos	Moreton Bay, Australia	Boxshall (2018)
	Caligus epidemicus	Moreton Bay, Australia	Boxshall (2018)
Lutjanus fulvus Forster, 1801	Caligus mutabilis	Palmyra Atoll, Central Pacific	Soler-Jimenez et al. (2019)
Lutjanus griseus Linnaeus, 1758	Caligus atromaculatus Wilson, 1913	Florida	Cressey and Nutter (1987)
	Caligus bonito	Isla de Margarita,Venezuela	Fuentes Zambrano et al. (2003)
	Caligus bonito	Gulf of Mexico	Ho and Lin (2004)
	Caligus irritans Heller, 1869	Venezuela	Lagarde (1991)
	Caligus wilsoni Delamare Deboutteville and Nunes Ruivo, 1958	Charlotte Harbor, Florida	Cressey (1991)
Lutjanus guttatus Steindachner, 1869	Caligus diaphanus Nordmann, 1834	Jaramijó, Ecuador	Morales-Serna et al. (2016)
	Caligus mutabilis	Mexican Pacific	Morales-Serna et al. (2012), Morales-Serna et al. (2014)
	Caligus sclerotinosus	Bahía de Chamela,Mexican Pacific	Morales-Serna et al. (2015)
Lutjanus jocu Bloch and Schneider, 1801	Caligus asperimanus	Carrie Bow Cay, Belize	Cressey (1991)
	Caligus asperimanus	off the coast of Rio de Janeiro, Brazil.	Oliveira et al. (2020)
Lutjanus johnii Bloch, 1792	Caligus asperimanus	India Coast	Pilla et al. (2012)
	Caligus auriilus Boxhall and Barton, 2023	Australia	Boxshall and Barton (2023)
	Caligus chiastos	Malaysia	Venmathi Maran et al. (2009)
	Caligus dussumieri	Australia	Boxshall and Barton (2023)
Lutjanus monostigma Cuvier, 1828	Caligus mutabilis	Palmyra Atoll, Central Pacific	Soler-Jimenez et al. (2019)
Lutjanus malabaricus	Caligus malabaricus	Malacca Strait, Malaysia	Leong (1984)
	Caligus torpedinis (as C. rotundigenitalis)	India	Pillai (1967)
Lutjanus novemfasciatus Gill, 1862	Caligus bonito	Mexican Pacific	Ho and Lin (2004), Morales-Serna et al. (2012)
Lutjanus peru Nichols and Murphy, 1922	Caligus mutabilis	Mexican Pacific	Morales-Serna et al. (2012), Morales-Serna et al. (2015)
Lutjanus peru Nichols & Murphy, 1922	Caligus diaphanus	Bahía de Chamela,Mexican Pacific	Morales-Serna et al. (2014)
	Caligus sclerotinosus	Bahía de Chamela,Mexican Pacific	Morales-Serna et al. (2014)
Lutjanus rivulatus Cuvier, 1828	Caligus nengai Rangnekar, Rangnekar & Murti, 1953	Taiwan	Ho and Lin (2004)
	Caligus dussumieri	India	Pilla et al. (2012)
Lutjanus russellii Bleeker, 1849	Caligus quadratus	Taiwan	Ho and Lin (2004)
	Caligus torpedinis (as C. rotundigenitalis)	Taiwan	Ho and Lin (2004)
	Caligus pagrosomi Yamaguti, 1939	Taiwan	Ho and Lin (2004)
	Caligus laticaudus	Taiwan	Ho and Lin (2004)
Lutjanus synagris Linnaeus, 1758	Caligus asperimanus	off the coast of Rio de Janeiro, Brazil.	Oliveira et al. (2020)
	Caligus asperimanus	Carrie Bow Cay, Belize	Cressey (1991)
	Caligus atromaculatus	Venezuela	Lagarde (1991)
	Caligus praetextus Bere, 1936	Charlotte Harbor, Florida	Cressey (1991)
	Caligus rufimaculatus Wilson, 1905	Florida and the Gulf of Mexico	Cressey (1991)
	Caligus praetextus	Belize; Florida	Bere (1936), Cressey (1991)
Lutjanus vitta Quoy and Gaimard, 1824	Caligus laticaudus	Taiwan	Ho and Lin (2004)
	Caligus torpedinis (as C. rotundigenitalis)	Taiwan	Ho and Lin (2004)
Lutjanus vivanus Cuvier, 1828	Caligus asperimanus	off the coast of Rio de Janeiro, Brazil.	Oliveira et al. (2020)
Lutjanus spp.	Caligus productus Dana, 1852	Mexican Pacific	Morales-Serna et al. (2012)

Species of Caligus, belonging to the bonito-group, are known from a variety of lutjanid hosts around the world. Caligus asperimanus and C. mutabilis exhibit a broad distribution and host range, having been reported from up to seven different lutjanid hosts in different regions, including Belize (Cressey 1991), the Bahamas, Brazil (Oliveira et al. 2020) and India (Pilla et al. 2012). While about three-quarters of reports of species of the bonito-group infecting lutjanids originated from North and South America, four species have been documented as infecting commercially exploited lutjanids from Asia, including L. johnii recorded from the coast of India (Pilla et al. 2012), L. malabaricus from the Malacca Strait and Terengganu Coast, Malaysia (Leong 1984), L. argentimaculatus from the Philippines (Ho et al. 2004) and L. russellii from Taiwan (Ho and Lin 2004).

In Malaysia, out of the 20 species of fish previously reported to serve as hosts for caligid copepods, three species of lutjanids are known to collectively host four species of Caligus: Lutjanus erythropterus hosts C. chiastos and C. torpedinis; L. johnii hosts C. chiastos; and L. malabaricus hosts C. malabaricus (Venmathi Maran et al. 2009).

Caligus dussumieri is assigned to the bonito-group because of the presence of three plumose setae on the distal exopodal segment of leg 1 and a row of stout denticles along the outer margin of the second endopodal segment of leg 2 (Boxshall and Barton 2023). It also shares two additional characteristics common to members of this species group: a 3-segmented leg 4 with four spines on the second exopodal segment and the presence of a small blunt posterior process on the proximal segment of the antenna. The bonito-group is currently composed of 20 species: C. asperimanus Pearse, 1951, C. asymmetricus Kabata, 1965, C. bonito Wilson C.B., 1905, C. caudatus Gnanamuthu, 1950, C. chamelensis Morales-Serna, Pinacho-Pinacho, Gómez and Pérez-Ponce de León, 2014, C. cossacki Bassett-Smith, 1898, C. dussumieri Rangnekar, 1957, C. formicoides Redkar, Rangnekar & Murti, 1949, C. grandiabdominalis Yamaguti, 1954, C. hoplognathi Yamaguti and Yamasu, 1959, C. infestans Heller, 1865, C. malabaricus Pillai, 1961, C. mutabilis Wilson, 1905, C. omissus Cressey and Cressey 1980, C. pauliani Nuñes-Ruivo & Fourmanoir, 1956, C. phipsoni Basset-Smith 1898, C. quadratus Shiino, 1954, C. tenuifurcatus Wilson, 1937, C. timorensis Izawa, 1995, and C. triabdominalis Byrnes, 1987 (Boxshall 2018, Ohtsuka and Boxshall 2019, Kamanli 2020). Caligus dussumieri along with C. caudatus, C. formicoides and C. timorensis were recently added to bonito-group after the species were transferred from Sinocaligus to Caligus (Boxshall and Barton 2023).

Caligids from the bonito-group have been recorded from another 30 families of fish, of which eight families (Carangidae, Coryphaenidae, Hemiramphidae, Istiophoridae, Nematistiidae, Pomatomidae, Scombridae and Sphyraenidae) are generally known as pelagic fish and 21 families are demersal fish from families Ariidae, Balistidae, Caesionidae, Centropomidae, Embiotocidae, Ephippidae, Gerreidae, Haemulidae, Kyphosidae, Mugilidae, Mullidae, Oplegnathidae, Polynemidae, Pomacentridae. Rhinobatidae, Sciaenidae, Serranidae, Siganidae and Sparidae. However, they appear to predominantly parasitise members of the family Scombridae. The fact that they primarily infect pelagic fish, but also use many minor demersal fish as hosts may indicate a possible history of evolutionary host-switching from pelagic to demersal fish.

An interesting example of host-switching during development is known in C. pauliani (previously reported as C. biseriodentatus), which infects different hosts at different life stages. The adult females are known from the frigate tuna Auxis thazard Lacepède, 1800, while premetamorphic adults and copepodid stages characterised mainly by smaller size, slender genital somites and not bearing eggs, are known from a variety of host species belonging to the genus Scomberomorus Lacepède, 1801. This form of host-switching appears to involve mated females only given that both pre-metamorphic adult females and males occur on the first host, which is where mating takes place, while only the mated females are known from the second host where the metamorphic developmental changes are completed. Cressey and Cressey (1980) speculated that host-switching might have resulted from predatory activities of the host because A. thazard is known as a common and important prey item for many larger fishes (Frimodt 1995).

The bonito-group has a broad distribution in low to middle latitudes across all oceans, with a denser concentration in the Indo-Pacific. The distribution of species infecting Lutjanidae is primarily concentrated in low latitudes due to the abundance of lutjanid fish in tropical and subtropical areas, as indicated in Fig. 6. In Malaysia, two caligids belonging to the bonito-group (C. dussumieri and C. malabaricus) have been documented in association with two lutjanid fish species (present study and Leong (1984)). Notably, the exploration of caligid copepod diversity in neighbouring Southeast Asian countries has been limited, reflecting a broader scarcity of research on Caligidae in the region. In addition to Malaysia records, a total of five caligids species from the bonito-group have been identified from Southeast Asian countries. These include C. bonito from E. affinis and C. formicoides from D. elopsoides from Vietnam (Truong et al. 2022,) C. grandiabdominalis from Caesio cuning Bloch, 1791 in Indonesia (Yamaguti 1954), C. pauliani recorded from Scomberomorus spp. from Thailand, the Philippines and Indonesia (Cressey and Cressey 1980); and C. quadratus on Siganidae and Mullidae in the Philippines and Indonesia (Ho et al. 2004, Yuniar et al. 2007). This underscores the need for further investigations to improve our understanding of caligid copepod diversity and distribution in Southeast Asian waters.

Figure 6.  

Geographical distribution of species belonging to the bonito-group within Caligus.

Acknowledgements

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