540 Chiang Mai J. Sci. 2012; 39(3)

Chiang Mai J. Sci. 2012; 39(3) : 540-544http://it.science.cmu.ac.th/ejournal/Short Communication

Thai Medaka, Oryzias minutillus Smith, 1945(Beloniformes: Adrianichthyidae): a New HostSpecies of Clinostomum complanatumMetacercariae (Digenea: Clinostomatidea) and theSurface Topography by Using SEMArin Ngamniyom [a], Manaporn Manaboon [b] and Busaba Panyarachun*[c][a] Faculty of Environmental Culture and Ecotourism, Srinakharinwirot University, Bangkok 10110, Thailand.[b] Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.[c] Department of Anatomy, Faculty of Medicine, Srinakharinwirot University, Bangkok 10110, Thailand.*Author for correspondence; e-mail: ngamniyom.a@gmail.com, busaba@swu.ac.th

Received: 15 December 2011Accepted: 13 April 2012

ABSTRACT The aim of this study was to describe the occurrence of Clinostomum complanatum

metacercariae infecting Thai medaka (Oryzias minutillus), a new intermediate host, collectedfrom Pathum Thani province, Thailand. A total of 533 fish collected from 5 localities included74 infected fish, 10.7% of prevalence, 0.15 of mean abundance and 1.4 of mean intensity forthe fluke. The worms were 3.58 mm in length and 0.90 mm in width. The oral suckers were0.20 mm long and 0.22 mm wide. The ventral sucker was 0.44 mm long and 0.46 mm wide.The surface topography showed structural-systematic features under scanning electronmicroscopy. This report is the first record of C. complanatum in Oryzias fish and may contributeto the knowledge of clinostomatids, regarding the host diversity and systematic morphologyof tegumental trematodes.

Keywords: Thai medaka, Oryzias minutillus, Clinostomum complanatum, tegument

1. INTRODUCTIONAmong the fish of the genus Oryzias,

medaka fish are a common model organismutilized for experiments in various fields [1].The Thai medaka (Oryzias minutillus), thesmallest species of the genus Oryzias, isdistributed throughout Thailand. The habitatsof this species are shallow ponds, ditches andpaddy fields [2].

The genus Clinostomum Rudolphi, 1819(Clinostomidae) is a parasite of several speciesof freshwater fish, e.g., carp (Cyprinus

carpio), blackchin tilapia (Sarotherodonmelanotheron), Capoeta capoeta gracilisand Aphanius dispar [3-6]. In fish, theparasites of this genus are the prevalence intropical and subtropical regions whichinclude C. complanatum, C. marginatum,C. philippinensis and C. cutaneum [7-10].Clinostomum infection in fish is reportedto cause yellow grub disease. Clinostomumparasites require freshwater snails and fishas intermediate hosts and birds as definitive

Chiang Mai J. Sci. 2012; 39(3) 541

Figure 1. The collection sites in Pathum Thaniprovince (a). C. complanatum metacercariaein Thai medaka (b). A histological view ofC. complanatum in fish (c). Acetic carmine& fast green stained (d) and genital complexof C. complanatum (e).

hosts [11]. However, no previous reportsof Clinostomum spp. in the Oryzias fishhave been recorded.

Therefore, the aim of this study is toreport a novel finding of Thai medaka as anew fish host of C. complanatum metacercariae.In addition, we investigated the tegumentalsurface of this worm with scanning electronmicroscopy (SEM).

2. MATERIALS AND METHODSA total of 533 Thai medaka were

collected from the ponds of Pathum Thaniprovince, Thailand from March to June2011(Figure 1a). Clinostomum sp. were isolatedfrom beneath the skins of the infected fish(Figure 1b). Twenty-five parasites werestained with acetic carmine & fast green [12]and observed under a light microscope.Histological sections of infected fish withparasites were also obtained (Figure 1c andd).

C. complanatum were identified with theKey to the Trematoda of Kanev et al. [13]and the morphological description of C.

complanatum by Caffara et al. [14]. The glossaryof Abidi et al. [15] was the source of themorphological terms used for helminths.Prevalence, mean abundance and meanintensity were determined according to Bushet al. [16]. Thirty specimens were subjectedto SEM according to the method ofPanyarachun et al. [17].

3. RESULTS AND DISCUSSIONIn 74 infected fish, the prevalence was

10.7% ± 1.7 (mean ± SE), the mean abundancewas 0.15 ± 0.02 and mean intensity was 1.4 ±0.2 in Pathum Thani province (Table 1). Inmany reports, freshwater fish have beenrecorded as intermediate host of C.complanatum [9, 13, 26, 27]. Our findingconfirmed that C. complanatum have beendistributed among the smallest fish ofOryzias species.

The wormlike bodies appeared tongue-shaped and were bluntly rounded atthe anterior and posterior ends. Fiftymetacercariae from the 5 localities were 3.58± 0.09 mm (mean ± SE) in length and 0.90 ±0.07 mm in width. The oral sucker was 0.20± 0.06 mm in length and 0.22 ± 0.05 mm inwidth. The ventral sucker was in the anteriorthird of the body and was 0.44 ± 0.06 mmlong and 0.46 ± 0.07 mm wide (Figure1d andTable 2).

In genital complex, the anterior testicularlobe was lined in the middle third of body,and the posterior lobe was lined in the anteriorpart of the posterior third. Two testicularlobes were separated by intertestiscular space.The uterus extended from posterior regionof ventral sucker to intertesticular space. Thecirrus sac was on right side of the anteriortestis with oval-shape. The small ovary wassituated between the testes on the right sideand was positioned between the cirrus anduterus (Figure 1e). The morphological featuresof the genital complex corresponded to the

542 Chiang Mai J. Sci. 2012; 39(3)

Table 1. Features of Thai medaka infected with C. complanatum from natural habitatsof Pathum Thani Province, Thailand.

descriptions of C. complanatum by Caffaraet al. [14]. The shape of C. complanatumin Thai medaka resembled to thepreviously description reported by Malekand Mobedi [5] and Gholami et al. [18] inother fish host species. In Thai medaka,the parasite had a relatively small and shortbody, oral sucker and ventral sucker interms of both length and width comparedwith the corresponding measurements ofC. complanatum in S. melanotheron [4] andAphanius dispar [18].

The oral sucker was characterized by twocollar-like rings and covered by pits, ridgesand dome-like papillae (Figure 2a, Figure 2b).Around the oral opening, the inner area ofthe surface was corrugated with ridgesseparated by pits (Figure 2c). The pits andridges on the inner surface were smootherthan those on the surface of the first collar-like ring (Figure 2b-d). The second collar-like

ring bore abundant papillae and wascomposed of two or three glandular pores(Figure 2e). Spines were not found in theanterior region. The ventral suckerexhibited sponge-like characters, and thedome-like papillae were present around themargins of the ventral sucker with spines(Figure 2f). These papillae were composedof a meshwork of grooves or foldsseparated from another one by pits orridges (Figure 2g. In the middle part ofthe ventral surface, spines were distributedthroughout the posterior end of the ventralportion (Figure 2h, Figure 2j). The rod-like spines were surrounded by the first tothe fifth or sixth cytoplasmic ridges. Thecytoplasmic ridge was interconnected withanother cytoplasmic ridge by an outerridge (Figure 2i). The spines in the middlearea were shorter than those in theposterior area. The dorsal surface was

Table 2. Morphometric data on C. complanatum in Thai medaka.

Locality Number

ofspecimen

Body (mean ± SE)

12345

Total

101010101050

3.19 ± 0.063.51 ± 0.093.81 ± 0.103.40 ± 0.104.01 ± 0.083.58 ± 0.09

length(mm) width(mm)

0.85 ± 0.040.91 ± 0.050.79 ± 0.110.84 ± 0.080.94 ± 0.050.90 ± 0.07

Oral sucker

length width

0.18 ± 0.060.20 ± 0.040.18 ± 0.070.19 ± 0.050.24 ± 0.070.20 ± 0.06

0.21 ± 0.040.23 ± 0.060.20 ± 0.050.24 ± 0.080.22 ± 0.040.22 ± 0.05

Ventral sucker

length width

0.44 ± 0.100.44 ± 0.040.42 ± 0.050.46 ± 0.040.45 ± 0.07 0.44 ± 0.06

0.44 ± 0.090.45 ± 0.060.45 ± 0.060.47 ± 0.080.48 ± 0.080.46 ± 0.07

Locality Total of fish

sample Infected fishprevalence

(%)mean

abundance mean intensity

12345

Total

11110398121100533

1417811774

12.616.58.29.17

10.7 ± 1.7

0.120.200.110.200.10

0.15 ± 0.02

11.21.42

1.61.4 ± 0.2

Chiang Mai J. Sci. 2012; 39(3) 543

Figure 2. A ventral surface of C. complanatumwith oral sucker (OS), ventral sucker (VS), thefirst collar-like ring (1st CL) and the secondcollar-like ring (2nd CL) (a). The surface ofthe oral sucker with grooves (gr) and papillae(pa) (b). A higher magnification of the oralsucker covered by ridges (ri) and pits (pi), andpores of glands (gc) (c, d, e). A ventral surfacewith ventral sucker, grooves, folds (fo),papillae and spines (sp) (f). A highermagnification of the ventral sucker (g). Thespines surrounded by cytoplasmic ridges (cr)(h). The first-sixth cytoplasmic ridges (1st-6thcr) surrounding spines (i). The long spines inthe middle to posterior region (j). A dorsalsurface of anterior and posterior regions withcobblestone-like units (cu) (k, l).

a b

c

d

e

characterized by cobblestone-like units. Theshort spines and cytoplasmic ridge werepoorly developed. The cytoplasmic ridgesconstituted the first to second ridges (Figure2k, Figure 2l).

The tegumental morphology of C.complanatum in Thai medaka corresponded wellwith the morphology described by Abidi etal. [15] for the tegumental morphology in C.complanatum from the banded gourami.However, in the banded gourami, the spineswere surrounded by the first to thirdcytoplasmic ridges. In spices related to C.complanatum, Marwan and Mohammed [19]reported that the cytoplasmic ridgessurrounded the single or double spines.

4. CONCLUSIONSThe present study is the first report of C.

complanatum in Thai medaka in a naturalenvironment. To our knowledge, thefinding that C. complanatum occurs inThai medaka may serve to increaseknowledge on the host diversity ofclinostomatids, although the accuracydetermination of C. complanatum (s) byusing molecular biology approach remainsto be investigated.

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