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Journal of Parasitic Diseases: Official Organ of the Indian Society for Parasitology logoLink to Journal of Parasitic Diseases: Official Organ of the Indian Society for Parasitology
. 2012 Feb 15;36(2):184–196. doi: 10.1007/s12639-012-0101-8

Community ecology of the metazoan parasites of freshwater fishes of Kerala

M Razia Beevi 1,✉, S Radhakrishnan 2
PMCID: PMC3427673  PMID: 24082525

Abstract

The prevalence and mean intensity of metazoan parasite infection, the community characteristics (richness index, dominance index, evenness index and Shannon index of diversity) and the qualitative similarity of the metazoan parasite fauna among the species and families of the fishes were determined of 13 fish species of freshwater fishes of Kerala belonging to seven families. The metazoan parasite fauna of this geographical area is very diverse; it consisted of 33 species of parasites belonging to seven major taxa: ten species of Monogenea, nine Digenea, two Cestoda, six Nematoda, three Acanthocephala, two Copepoda and one Isopoda. Prevalence of infection ranged from 32.9% (Puntius vittatus) to 87.1% (Mystus oculatus) and mean intensity from 3.8 (Puntius vittatus) to 27.6 (Aplocheilus lineatus). The infra- and component communities of parasites were somewhat characteristic. The dominance pattern of the major taxa was in the order Digenea > Nematoda > Monogenea = Acanthocephala > Cestoda = Copepoda > Isopoda. Macropodus cupanus harboured the richest fauna and Puntius vittatus had the least rich fauna. The parasite fauna of A. lineatus was the most heterogeneous and that of M. cavasius, the most homogeneous. The diversity of the parasite fauna was the greatest in M. cavasius and the least in A. lineatus. The parasite faunas of A. lineatus and M. cupanus and of M. cavasius and M. oculatus were similar. However, in spite of the taxonomic nearness and the similarity of the habits and habitats of the four species of cyprinids (P. amphibius, P. filamentosus, P. sarana and P. vittatus), their parasite fauna were qualitatively very dissimilar–of the seven species of parasites encountered in them only one was shared by the four host species. The cyprinid, Rasbora daniconius, had its own characteristic component community of parasites consisting of six species none of which was shared by the other four cyprinids. The richest parasite fauna was that of the family Cyprinidae followed by that of Channidae and the poorest of Belonidae. The most homogeneous parasite fauna was that of Bagridae and the most heterogeneous that of Cyprinodontidae. The parasite fauna of Cyprinodontidae and Belontidae were qualitatively very similar. The results indicate that the freshwater fishes of the southwest cost of India harbour a rich and diverse metazoan parasite fauna, which is as rich and diverse as that of the marine fishes of this area. The results also suggest that carnivorous/omnivorous fish species harbour richer and more heterogeneous component communities of parasites than herbivorous species implying that the feeding habits of fishes is a major factor deciding their parasite faunas.

Keywords: Dominance index, Evenness index, Freshwater fish parasites, Jaccard index, Parasite community ecology, Richness index, Shannon index of diversity, Species overlap

Introduction

Parasite fauna of marine fishes of the southwest coast of India is well studied (Natarajan 1975; Radhakrishnan and Nair 1980; Pillai 1985; Bijukumar 1996a, b; Santhosh 2001). But, no comparable information on freshwater fishes of the region is available. Marine fishes are generally supposed to harbour much more diverse and rich parasite fauna than freshwater fishes (Kinne 1985; Sindermann 1990; Rohde 1993). Parasite fauna of omnivorous/carnivorous fishes are reported to be richer and more diverse than that of herbivorous fishes (Moravec 1985; Zaman and Leong 1987a, b; Wierzbicka 1991). The present study was an attempt at bringing out the community characteristics of the metazoan parasite fauna of 13 species of freshwater fishes distributed in Kerala waters.

Materials and methods

Fortnightly collections of 13 species of fishes belonging to seven families were made by using cast nets, from Vellayani Lake, Killiayar River and Chackai canal, Trivandrum, Kerala (8°2′; 8°9′ N lat.; 76°6′; 77°4′ E long.) during the year 1990. Fresh fishes were examined by total parasitological dissection (Fernando et al. 1972; Kennedy 1979). The taxonomic positions, the location and the number of parasite in each fish and each location were recorded of parasites encountered in each fish. From the data community characteristics of the parasite fauna were determined based on the measures as suggested by Leong and Holmes (1981).

  1. Prevalence of infection (P) = percentage of fish infected.

  2. Mean intensity of infection (MI) = average number of parasites per infected fish.

  3. Abundance (A) = percentage of each taxon of parasite per host species.

  4. Proportion (P) = total No. of parasites in a host species (100 infected fishes)/total number of parasites from all host fishes, calculated as Total MI × 100/(∑Total MI × 100)

  5. Dominance Value (DV) = No. of parasites in each major taxon in a host species or family/Total No. of parasites in that host species or family × 100).

  6. Total number of parasites (N)

  7. Number of species (S) and number of major taxonomic group (major taxa = K) of parasites.

  8. Richness Index (RI) = (S−1)/loge N

  9. Dominace Index (DI) = ∑ (DVi /100)2

  10. Evenness Index (EI) = (Homogeneity = Relative Diversity) = H/loge, where H = Shannon Index of Diversity

  11. Shannon Index of Diversity = SI = H = {(n loge n)−(∑fi loge fi)}, where, n = ∑fi; fi = DV of parasite taxa in a host species/family.

  12. Jaccard Index of species overlap (J) = {(100 c)/(a + b) – c}, where, a = No. of species of parasites in host A; b = No. of species of parasites in host B; c = No. of species of parasites shared by hosts A and B.

Results

The different species and families of fishes examined and the total number of fish examined in each species are shown in Table 1. The list of parasites and their distribution in host fishes are presented in Tables 2 and 3. The overall nature of metazoan parasitic infection in different species and families of freshwater fishes is given in Tables 4 and 5, respectively. The community characteristics of the parasite fauna in different species and families of fishes are presented in Tables 6 and 7, respectively. Parasite species overlap (= similarity of the parasite fauna) in different species and families fishes is given in Tables 8 and 9, respectively.

Table 1.

Species and families of freshwater fishes examined and the total number of fish examined in each species

Name of Host Number examined Family
Puntius amphibius (Valenciennes) 339 Cyprinidae
Puntius filamentosus (Valenciennes) 191
Puntius sarana (Hamilton) 76
Puntius vittatus Day 213
Rasbora daniconius (Hamilton) 317
Aplocheilus lineatus (Valenciennes) 240 Cyprinodontidae
Mystus cavasius (Hamilton) 174 Bagridae
Mystus oculatus (Valenciennes) 202
Macropodus cupanus Cuvier 216 Belontidae
Heteropneustes fossilis (Bloch) 244 Heteropneustidae
Xenentodon cancila (Hamilton) 212 Belonidae
Channa gachua Hamilton 106 Channidae
Channa striata (Bloch) 104
Total 2,634
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Table 2.

Distribution of metazoan parasites in 13 species of freshwater fishes of Kerala (p present)

Parasite species/group Fish species
Puntius amphibius Puntius filamentosus Puntius sarana Puntius vittatus Rasbora daniconius Aplocheilus lineatus Mystus cavasius Mystus oculatus Macropodus cupanus Heteropneustes fossilis Xenentodon cancila Channa gachua Channa striatus
Monogena
 Ddactylogyrus cauveryi Tripathi p
 D. daniconius Razia Beevi and Radhakrishnan p
 D. arwetrabus Razia Beevi and Radhakrishnan p
 Dactylogyroides macracanthus Tripathi p
 D. gussevii Razia Beevi and Radhakrishnan p
 Ancyrocephalus acqualis forma travencoriensis Razia Beevi and Radhakrishnan   p
 Neomuraytrema tengra Tripathi p p
 Haliotrema sp. p
 Diplozoon indicum Dayal p  
 Neodiplozoon barbi Tripathi p
Digenea
 Clinostomum sp. 1 metacercaria p p p p
 Clinostomum sp. 2 metacercaria p
 Clinostomum sp. 3 metacercaria p
 Euclinostomum heterostomum Rudolphi p
 Diplostomum metacercaria p
 Neodiplostomum sp. Metacercaria p p
 Masenia fossilis Gupta p
 Eumasenia moradabadensis Srivastava p p
 Acanthostomum sp. p p p
Cestoda
 Senga malayana Fernando and Furtado p
 Neogryporhynchus sp. Plerocercus p
Nematoda
 Paracamallanus furtadoi Petter p
 Paracamallanus sp.   p
 Procamallanus sp. p p p p
 Spirocamallanus sp. p p
 Philometra lateolabracis (Yamaguti) p
 Pseudocapillaria indica Moravec et al. p
Acantho-cephala
 Pallisentis nagpurensis Bhalerao p p p p p
 Arythmorhynchus platysomi George and Nadakkal   p p p
Copepoda
 Lamproglena krishnai Thomas and Hameed p
 Lernaea bengalensis Gnanamuthu p
Isopoda
 Alytropus typus M. Edwards p
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Table 3.

Distribution of metazoan parasites in 7 families of freshwater fishes of Kerala (p present)

Parasite species/group Fish family
Cyprinidae Cyprinodontidae Bagridae Belontidae Heteropneustidae Belonidae Channidae
Monogenea
 Ddactylogyrus cauveryi Tripathi p
 D. daniconius Razia Beevi and  Radhakrishnan p
 D. arwetrabus Razia Beevi and  Radhakrishnan p
 Dactylogyroides macracanthus Tripathi p
 D. gussevii Razia Beevi and Radhakrishnan p
 Ancyrocephalus  acqualis forma  travencoriensis  Razia Beevi and  Radhakrishnan p
 Neomuraytrema tengra Tripathit p
 Haliotrema sp. p
 Diplozoon indicum Dayal p
 Neodiplozoon barbi Tripathi p
Digenea
 Clinostomum sp. 1 metacercaria p
 Clinostomum sp. 2 metacercaria p
 Clinostomum sp. 3 metacercaria p
 Euclinostomum heterostomum Rudolphi p
 Diplostomum metacercaria p
 Neodiplostomum sp. Metacercaria p p
 Masenia fossilis Gupta p
 Eumasenia moradabadensis Srivastava p
 Acanthostomum sp. p p p
Cestoda
 Senga malayana Fernando and Furtado p
 Neogryporhynchus sp. Plerocercus p
Nematoda
 Paracamallanus furtadoi Petter p
 Paracamallanus sp. p
 Procamallanus sp. p p p p
 Spirocamallanus sp. p
 Philometra lateolabracis (Yamaguti) p
 Pseudocapillaria indica Moravec et al. p
Acantho-cephala
 Pallisentis nagpurensis Bhalerao p p p p p
 Arythmorhynchus platysomi George and Nadakkal p p p
Copepoda
 Lamproglena krishnai Thomas and Hameed p
 Lernaea bengalensis Gnanamuthu p
Isopoda
 Alytropus typus M. Edwards p
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Table 4.

Prevalence (P = %), MI mean intensity, A abundance, DV dominance value and proportion of metazoan parasites in different species of freshwater fishes of Kerala

Fish species/Family Number examined Number infected Number of parasites Total Monogenea Digenea Cestoda Nematoda Acantho-cephala Copepoda Isopoda Proportion
Puntius amphibius 339 194 2,311 P 57.2 12.4 47.5 8.6
MI 11.9 9.2 11.7 1.4 0.0932
A 6.8 1.1 5.6 0.1
DV 12.3 16.8 81.5 1.73
P. filamentosus 191 81 446 P 42.4 33.5 24.1
MI 5.5 5.4 2.2 0.0431
A 2.3 1.8 0.5
DV 2.4 77.1 22.9
P. sarana 76 36 236 P 47.4 10.5 44.7
MI 6.6 5.6 5.6 0.0513
A 3.1 0.6 2.5
DV 1.3 19.1 80.9
P. vittatus 213 70 269 P 32.9 0.0 32.86
MI 3.8 3.84 0.0301
A 1.3 0.0 1.26
DV 1.4 0.0 100.0
Rasbora daniconius 317 193 1,816 P 60.9 17.7 51.4 9.8
MI 9.4 5.7 8.9 1.6 0.0736
A 5.7 1.0 4.6 0.2
DV 9.7 17.6 79.7 2.7
Aplocheilus lineatus 240 177 4,882 P 73.8 69.2 1.7 18.3
MI 27.6 28.4 1.5 3.8 0.2157
A 20.3 19.6 0.0 0.7
DV 26.1 96.4 0.1 3.4
Mystus cavasius 174 116 955 P 66.7 36.2 14.4 33.3 30.5
MI 8.2 7.7 2.4 3.8 3.7 0.0644
A 5.5 2.8 0.3 1.3 1.1
DV 5.1 50.5 6.3 22.8 20.4
M. oculatus 202 176 3,805 P 87.1 60.4 27.2 1.5 45.0 61.4
MI 21.6 17.1 6.0 1.7 6.0 6.8 0.1691
A 18.8 10.3 1.6 0.0 2.7 4.2
DV 20.3 54.8 8.6 0.1 14.3 22.1
Macropodus cupanus 216 131 870 P 60.6 54.2 8.8 12.0
MI 6.6 6.8 1.7 1.5 0.0519
A 4.0 3.7 0.1 0.2
DV 4.6 91.7 3.68 4.60
Heteropneustes fossilis 244 198 1,521 P 81.1 1.6 79.9 8.2
MI 7.7 2.8 7.5 2.6 0.0601
A 6.2 0.0 6.0 0.2
DV 8.1 0.7 95.9 3.4
Xenentodon cancila 212 142 722 P 67.0 54.7 21.2
MI 5.1 5.8 1.1 0.0398
A 3.4 3.2 0.2
DV 3.9 93.2 6.8
Channa gachua 106 69 425 P 65.1 21.7 54.7
MI 6.2 3.7 5.9 0.0482
A 4.0 0.8 3.2
DV 2.3 19.8 80.2
C. striatus 104 63 480 P 60.6 1.0 24.0 44.2 33.7 2.88
MI 7.6 1.0 4.6 5.6 2.9 1.67 0.0596
A 4.6 0.01 1.1 2.5 1.0 0.05
DV 2.6 0.2 24.0 54.0 20.8 1.04
Total 2,634 1,646 1,8738 P 62.5 17.9 32.8 0.2 18.8 13.1 2.4 0.1
MI 11.4 9.2 11.4 1.5 5.6 4.7 2.2 1.7
A 7.1 1.6 3.8 0.002 1.0 0.6 0.1 0.002
DV   23.1 52.7 0.03 14.8 8.6 0.7 0.03
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Table 5.

Prevalence (P = %), MI mean intensity, A abundance, DV dominance value and proportion of metazoan parasites in different families of freshwater fishes of Kerala

Fish species/family Number examined Number infected Number of parasites Total Monogenea Digenea Cestoda Nematoda Acantho-cephala Copepoda Isopoda Proportion
Cyprinidae 1136 574 5,078 P 50.5 15.0 41.7 2.7 2.6
MI 8.8 6.4 8.2 1.6 1.4 0.1120
A 4.5 1.0 3.4 0.0 0.0
DV 27.1 21.6 76.7 0.96 0.8
Cyprinodontidae 240 177 4,882 P 73.8
MI 27.6 0.3492
A 20.3
DV 26.1
Bagridae 376 292 4,760 P 77.7 49.2 21.3 0.8 39.6 47.1
MI 16.3 13.9 4.9 1.7 5.1 5.8 0.2064
A 12.7 6.8 1.0 0.0 2.0 2.8
DV 25.4 53.9 8.2 0.1 16.0 21.7
Belontidae 216 131 870 P 60.6
MI 6.6 0.0841
A 4.0
DV 4.6
Heteropneustidae 244 198 1,521 P 81.1
MI 7.7 0.0972
A 6.2
DV 8.1
Belonidae 212 142 722 P 67.0
MI 5.1 0.0644
A 3.4
DV 3.9
Channidae 210 132 905 P 62.9 11.0 0.5 39.52 21.9 16.7 1.4
MI 6.9 3.7 1.0 5.5 5.6 2.9 1.7 0.0868
A 4.3 0.4 0.0 2.2 1.2 0.5 0.0
DV 4.8 9.3 0.1 50.4 28.6 11.0 0.6
Total 2,634 1,646 18,738 P 62.5 17.9 32.8 0.2 18.8 13.1 2.4 0.1
MI 11.4 9.2 11.4 1.5 5.6 4.7 2.2 1.7
A 7.1 1.6 3.8 0.002 1.0 0.6 0.1 0.0
DV 23.1 52.7 0.03 14.8 8.6 0.7 0.0
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Table 6.

Community characteristics of metazoan parasites of 13 species of freshwater fishes of Kerala

Parameters Fish families/species Grand total
Cyprinidae Cyprinodontidae Bagridae Belontidae Heteropneustinidae Belonidae Channidae
Pa Pf Ps Pv Rd Total Al Mc Mo Total Mcu Hf Xc Cg Cs Total
Number examined 339 191 76 213 317 1136 240 174 202 376 216 244 212 106 104 210 2634
Number infected 194 81 36 70 193 574 177 116 176 292 131 198 142 69 63 132 1646
Total no. of parasites (N) 2,311 446 236 269 1816 5078 4882 955 3805 4760 870 1521 722 425 480 905 6513
No. of species of parasites (S) 3 3 3 1 6 14 5 4 5 5 6 4 2 4 6 10 33
No. of taxa of parasites (K) 3 2 2 1 3 4 3 4 5 5 3 3 2 2 5 6 7
Prevalence (%) 57.2 42.4 47.4 32.9 60.9 50.5 73.8 66.7 87.1 77.7 60.6 81.1 67.0 65.1 60.6 62.9 62.5
Mean intensity (MI) 11.9 5.5 6.6 3.8 9.4 8.8 27.6 8.2 21.6 16.3 6.6 7.7 5.1 6.2 7.6 6.9 4.0
Abundance (A) 6.8 2.3 3.1 1.3 5.7 4.5 20.3 5.5 18.8 12.7 4.0 6.2 3.4 4.0 4.6 4.3 2.5
Proportion of parasites 0.0932 0.0431 0.0513 0.0301 0.0736 0.1120 0.2157 0.0644 0.1691 0.1275 0.0519 0.0601 0.0398 0.0482 0.0596 0.0868  
Dominance index (DI) 0.6924 0.6472 0.6914 1.0000 0.6674 0.6345 0.9312 0.3525 0.3773 0.3707 0.8448 0.9201 0.8735 0.6828 0.3921 0.3566  
Richness index on S (RI) 0.2824 0.3169 0.3083 0 0.7303 1.9158 0.5049 0.4469 0.5209 0.5408 0.7694 0.4515 0.1605 0.4671 0.7535 1.3781  
Richness index on K (RI) 0.2824 0.1584 0.1542 0 0.2921 0.4421 0.2525 0.4469 0.5209 0.5408 0.3078 0.3010 0.1605 0.1557 0.6028 0.7656  
Evenness index on S (EI) 0.4885 0.7759 0.7029 0 0.5311 0.4456 0.1449 0.8516 0.7217 0.7270 0.3116 0.1744 0.3579 0.7172 0.6601 0.6718  
Shannon index (H) 0.5367 0.5378 0.4872 0 0.5834 0.6177 0.1592 1.1806 1.1615 1.1700 0.3423 0.1916 0.2481 0.4971 1.0624 1.2037  
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Pa P. amphibius ,Pf P. filamentosus, Ps P. sarana, Pv P. vittatus, Rd R. daniconius, Al A. lineatus, Mc M. cavasius, Mo M. oculatus, Mcu M. cupanus, Hf H. fossilis, Xc X. cancila, Cg C. gachua, Cs C. striata

Table 7.

Community characteristics of metazoan parasites of seven families of freshwater fishes of Kerala

Parameters Cyprinidae Cyprino-dontidae Bagridae Belontidae Heteropneu-stidae Belonidae Channidae Total
Number examined 1136 240 376 216 244 212 210 2,634
Number infected 574 177 292 131 198 142 132 1,646
Total No. of parasites (N) 5,078 4,882 4,760 870 1,521 722 905 6,513
No. of species of parasites (S) 14 5 5 6 4 2 10 33
No. of taxa of parasites (K) 4 3 5 3 3 2 6 7
Prevalence (%) 50.5 73.8 77.7 60.6 81.1 67.0 62.9 62.5
Mean intensity (MI) 8.8 27.6 16.3 6.6 7.7 5.1 6.9 4.0
Abundance (A) 4.5 20.3 12.7 4.0 6.2 3.4 4.3 2.5
Proportion of parasites 0.1120 0.3492 0.2064 0.0841 0.0972 0.0644 0.0868
Dominance index (DI) 0.6345 0.9312 0.3707 0.8448 0.9201 0.8735 0.3566
Richness index on S (RI) 1.9158 0.5049 0.5408 0.7694 0.4515 0.1605 1.3781
Richness index on K (RI) 0.4421 0.2525 0.5408 0.3078 0.3010 0.1605 0.7656
Evenness index on S (EI) 0.4456 0.1449 0.7270 0.3116 0.1744 0.3579 0.6718
Shannon index K(H) 0.6177 0.1592 1.1700 0.3423 0.1916 0.2481 1.2037
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Table 8.

Parasite species overlap in different species of freshwater fishes of Kerala

Fish species S Pf Ps Pv Rd Al Mc Mo Mcu Hf Xc Cg Cs
Puntius amphibius (Pa) 3 1 1 1 0 0 0 0 0 0 0 0 0
20.0 20.0 33.3
P. filamentosus (Pf) 3 1 1 0 0 0 0 0 0 0 0 0
20.0 33.3
P. sarana (Ps) 3 1 0 0 0 0 0 0 0 0 0
33.3
P. vittatus (Pv) 1 0 0 0 0 0 0 0 0 0
Rasbora daniconius (Rd) 6 2 0 0 2 1 0 0 1
22.2 20.0 11.1 9.1
Aplocheilus lineatus (Al) 5 0 0 5 2 0 1 2
83.3 28.6 12.5 22.2
Mystus cavasius (Mc) 4 4 0 0 0 0 0
80.0
M. oculatus (Mo) 5 0 0 0 0 0
Macropodus cupanus (Mcu) 6 0 2 0 1 0
25.0 11.1
Heteropneustes fossilis (Hf) 4 0 0 1 1
14.3 11.1
Xenentodon cancila (Xc) 2 0 0 0
Channa gachua (Cg) 4 0 0
C. striata (Cs) 6 0
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Bold values are indicate results

Table 9.

Parasite species overlap in different families of freshwater fishes of Kerala

Fish family S Cyp Cyd Bag Bet Het Ben Cha
Cyprinidae (Cyp) 13 2 0 2 1 0 1
12.5 11.8 6.2 4.5
Cyprinodontidae (Cyd) 5 0 5 2 0 3
83.3 28.6 25.0
Bagridae (Bag) 5 0 0 0
Belontidae (Bet) 6 2 0 3
25.0 23.1
Heteropneustidae (Het) 4 2
16.7
Belonidae (Ben) 2
Channidae (Cha) 10
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Bold values are indicate results

Metazoan parasites occurred in all the 13 species. Of the 2,634 fishes examined, 62.5% harboured metazoan parasites and the average number of parasites was 11.4 per fish. Prevalence of infection was the highest in M. oculatus (87.1%) and the lowest in P. vittatus (32.9%). On the whole, in the carnivorous and omnivorous fishes prevalence of infection was comparatively higher than in the predominantly herbivorous species. The highest MI of metazoan parasites was noted in A. lineatus (27.6) and the lowest in P. vittatus (3.8); the former a predominantly carnivore (particularly larvivore) and the latter a herbivore. As with prevalence, MI was also was slightly higher in the carnivorous species than in the herbivorous. Proportion of metazoan parasites registered the maximum in A. lineatus (0.2157) and the lowest in P. vittatus (0.0301) (Table 4).

Of the 13 species of fishes examined 84.6% harboured digeneans, whereas only 7.7% harboured isopods. The percentage occurrence of the other major taxa of metazoan parasites was, Monogenea = 53.8%, Cestoda and Copepoda = 15.4% each, Nematoda = 61.5% and Acanthocephala = 38.5%. The dominance pattern of the major taxa of metazoan parasites in freshwater fishes of this region was in the order, Digenea > Nematoda > Monogenea > Acanthocephala > Cestoda = Copepoda > Isopoda (Table 2). The most dominant group of parasites was Digenea (DV = 52.7%) and the least were Cestoda and Isopoda (DV = 0.03%) (Tables 2, 3, 4).

Results of the family-wise comparison of parasitic infection (Table 5) showed that the highest prevalence of metazoan parasitic infection was in Heteropneustidae (81.1%) and the lowest in Cyprinidae (50.5%). Prevalences of infection in the other six families were, Bagridae = 77.7%, Cyprinodontidae = 73.8%, Belonidae = 67.0%, Channnidae = 62.9% and Belontidae = 60.6%. The highest MI was noted in Cyprinodontidae (27.6) and the lowest in Belonidae (5.1). In the other families MI varied between 6.6 and 16.3. The highest proportion of metazoan parasites was recorded in Cyprinodontidae (0.3492) followed by Bagridae (0.2064) and Cyprinidae (0.1120). The lowest proportion was noted in Belonidae (0.0644). In Belontidae it was 0.0841, in Channidae, 0.0868 and in Heteropneustidae, 0.0972.

Community ecology of metazoan parasite fauna in different species of fishes

The results are shown in Table 6. Each host species had a characteristic assemblage or community of parasites, which differed in several respects among the host species. Of the 13 host species, three (R. daniconius, M. cupanus and C. striatus) harboured six parasite species each and P. vittatus harboured only one. In the other hosts species, the number of parasite species varied between two and five. In M. oculatus and C. striatus the parasite fauna was constituted by five major taxa of parasites (Monogenea, Digenea, Cestoda, Nematoda and Acanthocephala in the former and Digenea, Nematoda, Acanthocephala, Copepoda and Isopida in the latter).

The parasite fauna was the richest in Macropodus cupanus (RI = 0.7694), which harboured six species of parasites belonging to three genera, closely followed by C. striata (RI = 0.7535) and R. daniconius (RI = 0.7303) both with six species of parasites represented by five major taxa in the former and three in the latter. The least rich fauna was that of P. vittatus in which only one species of parasite (Clinostomum sp. metacercaria) was encountered. The parasite fauna of A. lineatus was the most unevenly distributed or the most heterogeneous (EI = 0.1449) and that of M. cavasius was the most homogeneous (EI = 0.8516) followed by that of P. filamentosus (EI = 0.7759).

Barring, P. vittatus, which harboured only one species of parasite, dominance index was the highest (0.9312) for the parasite fauna of A. lineatus in which digeneans were a very dominant component constituting 96.4% of the total number of parasites in this fish. DIs were comparatively high in H. fossilis (0.9201), Xenentodon cancila (0.8734) and M. cupanus (0.8447). In H. fossilis nematodes and in M. cupanus digeneans dominated in the parasite fauna. In C. striata, M. oculatus and M. cavasius DI recorded comparatively low values (0.3921, 0.3773 and 0.3525, respectively) and in these species the parasite faunas were comparatively homogeneous.

Diversity of parasite fauna was the greatest for M. cavasius (H = 1.1806). In this species the parasite fauna represented by four species of parasites belonging to four major taxa was somewhat homogeneously distributed (EI = 0.8516). Diversity of the parasite fauna was the lowest in A. lineatus (H = 0.1592) in which five species of parasites belonging to three major taxa were encountered and of these digeneans were highly dominant (DV = 96.4%) over the other groups. In H. fossilis also diversity of parasite fauna was comparatively low (H = 0.1916); in this species the parasite fauna was represented by four species belonging to three major taxa, of which nematodes were very dominant (DV = 95.9%).

Qualitative similarity of the parasite fauna of the host fishes (Table 8) showed that there was relatively high similarity between the parasite fauna of A. lineatus and M. cupanus (Jaccard index = 83.3) as also between those of M. cavasius and M. oculatus (Jaccard index = 80.0). Of the six species of parasites encountered in A. lineatus and M. cupanus five were shared by the two hosts. Similarly, out of the five species of parasites harboured by M. cavasius and M. oculatus, four were shared by them. Only relatively lesser similarity was noted in the parasite fauna of the cyprinids; even though seven species of parasites were encountered in them only one species was shared by them.

Community ecology of metazoan parasite fauna in different families of fishes

The highest prevalence of metazoan parasitic infection was in Heteropneustidae (81.1%) and the lowest in Cyprinidae (50.5%). However, the highest number of species of parasites was recorded in Cyprinidae (13 belonging to four major taxa) and the lowest in Belonidae (2). Channidae harboured nine species of parasites belonging to six major taxa and Belontidae, six species belonging to three major taxa. In Cyprinidae the parasite fauna was predominated by monogeneans (eight species), whereas the most assorted fauna of parasites was in Channidae. Mean intensity recorded the highest in Cyprinodontidae (27.6) followed by Bagridae (16.3). Belontidae recorded the lowest MI (5.1). In the other families MI varied between 6.9 and 8.9 (Table 5).

The richest parasite fauna was that of Cyprinidae (RI = 1.9158) followed by that of Channidae (RI = 1.3781) (Table 7). In Cyprinidae 13 species of parasites representing four major taxa and in Channidae nine species representing six major taxa occurred. RI was 0.7694 in Belontidae (six species in three major taxa) and it was the lowest (0.1605) in Belonidae (two species belonging to two major taxa). Dominance index recorded high for Cyprinodontidae (0.9312), Heteropneustidae (0.9201), Belonidae (0.8735) and Belontidae (0.8448). In these cases Digenea (DV = 96.4%), Nematoda (DV = 95.7%), Monogenea (DV = 93.2%) and Digenea (DV = 91.7%) respectively dominated over the other taxa of parasites. The parasite fauna of Bagridae was the most homogeneous (EI = 0.7270) and of Cyprinodontidae, the most heterogeneous (EI = 0.1449). Diversity of parasite fauna war the greatest in Channidae (H = 1.2037). That of Bagridae was also high (H = 1.1700). Both host families had somewhat homogeneous parasite faunas, that of Bagridae being more evenly distributed than of Channidae and in both none of the parasite taxa being overly dominant. The lowest diversity index was recorded for Cyprinodontidae (H = 0.1592). That of Heteropneustidae was also low (H = 0.1916). In both cases the parasite assemblages were very heterogeneous (EI = 0.1449 and 0.1744, respectively) and they were dominated by Digenea (DI = 0.9312) and Nematoda (DI = 0.9201), respectively (Table 7).

Analysis of parasite species overlap in different host families (Table 9) showed that the parasite species were qualitatively very similar in Cyprinodontidae and Belontidae (Jaccard index = 83.3). Of the 11 species of parasites recorded from these two host families, five were shared by them.

Discussion

Overall nature of parasitic infections

Interspecific and interfamilial comparisons of metazoan parasitic fauna revealed that both prevalence and mean intensity were higher in carnivorous/omnivorous species/families indicating that feeding habit of the host is significant factor in determining the nature of parasitic faunas in them. As noted by Bibby (1972), Rampus (1975), Evans (1977), Lian and Leong (1979), Moravec (1985), Zaman and Leong (1987a, b) and Wierzbicka (1991), carnivorous/omnivorous species of fishes are more prone to parasitic infections as they stand higher chances of acquiring parasites, particularly heteroxenous forms than the herbivorous forms, which because of the restriction in food, do not have the chances of acquiring more infections nor more varied fauna of parasites.

Community ecology of metazoan parasite fauna

Kennedy et al. (1986) are of the view that compared to the parasite fauna of birds and mammals, that of freshwater fishes is poor and less diverse and that species richness and mean intensity of parasites of freshwater fishes is less than that of marine fishes. The present results corroborate both these contentions as only 33 species of metazoan parasites were encountered in 13 species of freshwater fishes as against 65 species from 13 species of marine fishes (Radhakrishnan and Nair 1980) and 50 from eight species of mullets (Santhosh 2001) from the same geographical area. Yet, such a generalisation may not always hold good as Bijukumar (1996a) found only 50 species of metazoan parasites in 21 species of marine flatfishes of the same region. It is to be noted in this context that the compound community of parasites (= local parasite fauna) is influenced by several factors and there could be even temporal differences in the nature of the compound communities (Holmes 1990). Further, there is evidence to show that the parasite communities of freshwater fishes are basically stochastic assemblages determined by events like chance introduction, colonization and extinction of parasites in a given region (Esch et al. 1988; Hartvigsen and Kennedy 1993; Kennedy 1993).

Carnivorous forms such as Channa spp., M. cupanus, Mystus spp. and H. fossilis harboured richer parasite faunas than the predominantly herbivorous forms. Moreover, the distribution of parasite species was somewhat more homogeneous in carnivorous forms than in herbivorous. Diversity index of parasite species was also comparatively higher in carnivorous forms than in herbivores. But results obtained for R. daniconius, a herbivore and X. cancila a carnivore, betray the general conclusions drawn above, the reasons for which remain elusive. However, since many other factors other than the feeding habit of the hosts are involved in deciding the nature of the parasite fauna of fishes, the results obtained for R. daniconius and X. cancila do not overrule the significant relation between feeding habit and nature parasite fauna of fishes.

Marine fishes generally have rich parasitic helminth communities (Holmes 1990; Rohde 1993; Thoney 1993). In conformity with this Radhakrishnan and Nair (1980) found that about 58% of the parasites in the marine fishes they examined were helminths and Bijukumar (1996a) found 75% of the parasites in flatfishes to be helminths. However, in mullets of Kerala waters the proportion of helminth parasites is only 42% (Santhosh 2001). The present results however show that in freshwater fishes also helminth parasite fauna is very dominant possibly even more than that in marine fishes; in the present study of the 33 parasites met with 30 (about 91%) were helminths.

Qualitative similarity of parasite fauna

Qualitative similarity of the parasite fauna has been very marked for the two herbivorous species, A. lineatus and M. cupanus and for the two bagrids, M. cavasius and M. oculatus, lending support to the fact that the feeding habit of the host species is a very significant factor in deciding the parasite fauna of the hosts. However, there has been no similarity between the parasite fauna of the channids, C. striata and C. gachua. Similarly, only very little similarity was recorded for the parasite faunas of the four cyprinids, P. amphibius, P. filamentosus, P. sarana and P. vittatus, and none of the parasites of the cyprinid, R. daniconius was shared by the other four. The reasons for the observed dissimilarity of the parasite fauna of closely allied hosts species is beyond comprehension. Bijukumar (1996b), who also reported on a similar situation in respect of Etroplus suratensis and E. maculatus, two closely allied Asian cichlids, in which also the metazoan parasite communities differed considerably in spite of the phylogenetic closeness of the two, their similar habits and habitats, attributed it to the interspecific differences inherent in parasitism. The fundamental stochastic nature of the component parasite communities of freshwater fishes might also have contributed to this end.

Acknowledgements

The authors are thankful to the Department of Aquatic Biology and Fisheries, University of Kerala, Trivandrum, for the facilities received. One of us (MRB) is grateful to the UGC for the award of JRF, during the tenure of which this work was carried out.

Contributor Information

M. Razia Beevi, Email: razia.mes@gmail.com.

S. Radhakrishnan, Email: dr_srk_aqb@yahoo.co.in

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