Abstract: Background and Objective: Fishes of the genus Mystus are the members of Bagridae family which occupy an important place in Godavari fishery. Two commonly available species, Mystus vittatus Bloch, 1800 and Mystus cavasius Hamilton, 1822 of River Godavari, Rajahmundry Andhra Pradesh serve as significant hosts for metazoa\n parasites. The present study was aimed to ascertain the population dynamics, community characteristics and the faunal similarity of the two bagridae fishes, Mystus vittatus (n = 116) and Mystus cavasius (n = 94) at both infra and component community level during the 2008-2009. Materials and Methods: Standard statistical analyses were conducted to study the parasitic communities of both the fishes. Jaccard’s similarity coefficient was used to observe the faunal similarity of both the fishes. Various parameters such as Shannon-wiener index (H'), evenness (E) and Simpson’s diversity indices were applied to the fully sampled metazoan infracommunities of both fishes. Mean-variance ratio described the distribution patterns of the parasites within the host. The correlation coefficient (R) explained the correlation between the standard length of host and parasitic abundance for all parasites. The Mann-Whitney U-test was applied to both the fishes to observe the influence of host sex on the overall parasitic abundance. Jaccard’s interspecific association was used to find out the interspecific association between each pair of parasite species within a same host. Results: A total of nine metazoan parasites were obtained from both the fishes during the research study. The present investigation includes five species, i.e., Haplorchoides macrones, Bifurcohaptor indicus, Thaparocleidus tengra, Raosentis podderi and Raosentis thapari that are common to both the species. On the other hand, Metacercaria Isoparorchis hypselobagri, Raosentis godavarensis and Argulus striatus occurred specifically in Mystus vittatus and Lamproglena hospetensis occur exclusively from Mystus cavasius. There were no core and secondary species in the parasitic communities of both the fishes. Host length and rate of parasitisation showed very less correlation. There was no influence of sex on the parasitisation. Over-dispersed distribution is the generalized pattern of distribution of macroparasites and all the parasites showed over-dispersed distribution patterns except Argulus striatus, which displayed a random distribution pattern. The higher JI values indicate that there is very less competition among species as they occupy different niches within the same host. Conclusion: Though, the faunal similarity of both the fishes was high but the parasitic communities of these fishes are less diverse, depauperate and non-interactive.
INTRODUCTION
River Godavari is highly renowned as for its vibrant environment, affluent nutrients, high productivity and potential field to carry out fishery research1. The genus Mystus Scolpoli, 1771 is the representative of the family Bagridae native to Asia and consists of 45 recognized species. Two species, Mystus vittatus Bloch, 1800 and Mystus cavasius Hamilton, 1822 are of common occurrence in the River Godavari2-4. Mystus, commonly known as Eti Jella, is one of the popular commercial fish highly relished in Southern India as delicious proteinaceous food and forms an important inland fishery in Indian subcontinent. Mystus vittatus, the striped dwarf catfish, is a species of catfish that grows upto a length of 21 cm and found in brackish water systems with marginal vegetation in lakes and swamps with a mud substrate of Asian countries like India, Pakistan, Sri Lanka, Nepal, Bangladesh and probably Myanmar. Mystus cavasius, the Gangetic mystus, is a species of catfish that grows to a length of 40 cm and found in Indian Subcontinent countries such as, India, Pakistan, Sri Lanka, Nepal and Myanmar. The pectoral spine of this species may be noxious and cause agonizing wounds. Both the population are known to be declining in recent past, due to their indiscriminate catching, pet trading and habitat destruction. Most of the work on the silurid fishes was concentrated on its breeding and culture techniques, embryonic and larval development, fecundity and sex ratio5-12. Parasites occupy a very decisive place in animal kingdom for their invasive adoption and harmful activities to host13,14. Every parasite residing in or on a fish impose some degree of detrimental effect on its host. Heavily infected fish shows an intermittent or inhibited growth. Extensive research conducted on parasitic infection in various freshwater fishes such as Clarias batrachus, Channa punctatus, Rita rita, Anabas testudineus and carps from all over the world15-27. Conversely, only a few surveys on parasite community structure of freshwater fishes were executed globally28-35. The silurid fishes of the genus Mystus serves as better hosts for the metazoan parasites. However, very less amount of work has been concentrated on the parasitic fauna of Mystus due to the poor diagnosis of the genus36,37. The composition of parasite community in a fish is influenced by many environmental factors such as the location of the habitat, season of the year, physio-chemical factors of water and fauna present in and around the habit. All these factors can add to the emergence of new species and may amplify the parasite species richness38-43. Also the diet, age, abundance of fish length, sex and interdependence of members of the parasite fauna within the fish and season are some other factors which directly persuade parasitic fauna of the host44-48. The community structure of parasites in a host is shaped by many factors such as the parasitic interaction in various trophic levels, food webs, competition and biodiversity around them. The ecological studies on the metazoan parasites of fish are incredibly scarce in Indian Sub-continent especially in Andhra Pradesh. There are no comparative studies on the parasitic community structure of the two Mystus species. A meticulous attempt was made to ascertain the parasite diversity of M. vittatus and M. cavasius at component and infra-community structural levels and to calculate the possible effect of host standard length and sex on its parasitic abundance.
MATERIALS AND METHODS
Study area: Godavari is the second longest river in India and often referred to as the Vriddh (Old) Ganga or the Dakshin (South) Ganga. The river is about 1,450 km (900 miles) long. It rises at Trimbakeshwar, near Nashik and Mumbai in Maharashtra around 380 km distance from the Arabian Sea but flows Southeast across South-central India through the states of Madhya Pradesh, Karnataka, Orissa and Andhra Pradesh and joins Bay of Bengal. At Rajahmundry, 80 km from the coast, the river splits into two streams, thus forming a very fertile delta. It is a seasonal river, widened during the monsoons and dried during the summers. Godavari river water is brownish. Some of its tributaries include Indravati river, Manjira, Bindusara and Sarbari49-51. Some important urban centers of Andhra Pradesh on its banks include Bhadrachalam, Rajahmundry and Narsapur (Fig. 1a-c). Godavari River is known for its lively environment, enriched with the nutrients proved to be a highly productive and prospective field to accomplish fishery research and fishing operations. The catchment area of the river has been estimated as 290,600 km.
The present study was designed to investigate the parasites of the Mystus vittatus and Mystus cavasius collected from the River Godavari, Rajahmundry Andhra Pradesh from local fish markets during 2008-2009. A total of 116 Mystus vittatus and 94 Mystus cavasius transported to the laboratory to screen the presence of parasites. Morphometric characters such as length, weight and sex of each fish was noted cautiously and all the organs were examined separately under the stereo zoom microscope (LM-52-3621 Elegant) and specific characters were observed under the Lynx Trinocular microscope (N-800 M). A conventional technique was followed to prepare permanent slides of the collected52.
| Fig. 1(a-c): | Centers of Andhra Pradesh, (a) Geographical map of India showing Godavari river flowing Andhra Pradesh state, (b) Andhra Pradesh River map and (c) River Godavari |
Statistical analysis: Monthly population dynamics of the parasites were calculated by employing standard statistical computations (prevalence, mean intensity, mean abundance, index of infection and standard deviation) using various statistical softwares. To study the seasonal impact, each annual cycle was classified into three seasons as follows:
Winter (November-February), summer (March-June) and rainy (July-October). The seasonal influence on the incidence of infection was analyzed by Chi-square test53. The structure of the component and infra communities of Mystus vittatus and Mystus cavasius was described following the terminologies of Margolis et al.54 and Bush et al.55. Parasite infracommunities were expressed by means of statistical computations i.e., prevalence, abundance and intensity, however component of communities are described in terms of species richness, mean abundance, mean intensity and community similarity such as diversity, dominance and evenness indices. Species classification was done according to Bush and Holmes56, as central/core species (if prevalence >66.6%), secondary species (prevalence between 33.3-66.6%) and satellite species (prevalence <33.3%) of the total number of fish analyzed. Dispersion index (DI) evaluated the dispersion pattern of parasite species. The distribution of parasites was classified as aggregated (DI>1.96), regular (DI<-1.96) and random (DI<1.96). The parasite diversity of the sample was calculated using Simpson diversity index (λ) and for infinite population, Shannon’s index of diversity (H’) was employed57. For evenness, Shannon-based evenness (E) was calculated. Host size is considered as the decisive factor in determining the parasitic communities in any host. Pearson linear correlation coefficient (r) determines the possible correlation between host standard length with prevalence and abundance of each parasite species respectively53. The existence of an association among species for measuring degree of association was done by Jaccard’s index (JI) whose value ranged between 0-1 and as the value approached to 1, indicated the high association among species. Mann-Whitney U-test was used as an indication to scrutinize the influence of host sex on the parasitic abundance. Community structure of parasites has been determined as a function of host habitats, sizes and sexes.
All the statistical tests were conducted using excel in SPSS, IBM 21.0, MS-Office and statistical significance level adopted was p<0.05.
RESULTS AND DISCUSSION
Nine metazoan parasites were obtained from both the fishes during the present investigation, i.e., Haplorchoides macrones, Bifurcohaptor indicus, Thaparocleidus tengra, Raosentis podderi and R. thapari, Metacercaria Isoparorchis hypselobagri, Raosentis godavarensis, Argulus striatus Lamproglena hospetensis, whose monthly population dynamics and seasonal influence were carefully studied with a prime focus on their individual community structure (Table 1).
Monthly population dynamics of the metazoan parasites in M. vittatus and M. cavasius and the seasonal influence on parasitization: In the present study, the prevalence was 100% in the months of February, August, September and October, moderate in April, June, July and December and least in the rest of the month for M. vittatus while M. cavasius showed the highest prevalence in the months January and July and least prevalence in the months of March and April (Fig. 2a-d). Remaining months depicted the moderate to high prevalence’s (Fig. 2a). Mean intensity and mean abundance were high in the months of July and August and higher index of infection was observed in August for M. vittatus (Fig. 2b-d). Similarly, M. cavasius showed high mean intensity, mean abundance and index of infection values in September and October (Fig. 2b-d). The season is also one of the main factors in structuring the parasitic community in the fish population58-60. Prevalence, mean intensity, mean abundance and index of infection were high in the rainy season, followed by winter season and least in summer season for both the fishes.
| Table 1: | Metazoan parasites of Mystus vittatus Bloch, 1800 and Mystus cavasius Hamilton, 1822 |
| Fig. 2(a-d): | Monthly population dynamics of total parasites of M. vittatus and M. cavasius, (a) Prevalence, (b) Mean intensity, (c) Mean abundance and (d) Intensity of infection |
However, the insignificant Chi-square values χ2 = 2.64, p = 0.267 for M. vittatus and χ2 = 2.45, p = 0.292 for M. cavasius at p<0.05 showed no influence of seasons on the parasitization (Table 2).
Component community structure of M. vittatus and M. cavasius: Of the nine metazoan parasites obtained from both the fishes 5 species i.e., H. macrones, B. indicus, T. tengra, R. podderi and R. thapari are common to both the species whereas Metacercaria I. hypselobagri, R. godavarensis and A. striatus occurred specifically in Mystus vittatus and L. hospetensis from M. cavasius (Table 1, 3, 4). Monogeneans (49.5%) predominated the parasitic community of M. vittatus followed by the digeneans (35.6%) whereas in M. cavasius, acanthocephalans (43.8%) conquered the parasitic community followed by the monogeneans (29.1%) (Table 5). Of the 116 hosts, 59 hosts (50.8%) of M. vittatus showed infection with any single parasitic group, 9 hosts (7.75%) were infected with any two parasitic groups and only 2 hosts (1.72%) showed infection with the 3 parasitic groups and none of the hosts showed infection with all the 4 parasitic groups (Table 6). On the other hand, of the 94 hosts, 39 hosts (41.4%) of M. cavasius showed infection with any single parasitic group, 20 hosts (21.2%) were infected with any two parasitic groups and only 5 hosts (5.3%) showed infection with 3 parasitic groups and none of the hosts showed infection with all the 4 parasitic groups (Table 6). Analysis on infestation with endo and ectoparasites shows that infestation with ecto helminth community (56.5%) was slightly more than endoparasitic community (43.5%) in M. vittatus whereas M. cavasius showed more endoparasitic infection (60.6%) than ectoparasites (39.3%). Alimentary gut, especially esophagus, stomach and intestine are the ideal locale of the endoparasites whereas gills and skin being much-preferred habitats of ectoparasites and parasites retain a commensalistic relationship with its host and do not create any nuisance although present in abundant number61. The number of parasites present in skin, gills, stomach and intestine of M. vittatus and M. cavasius was enumerated. Gills showed the maximum infection of 49.5% monogeneans, followed by the intestine (43.5%), swim bladder (4.5%) and skin (2.4%) in M. vittatus however, M. cavasius showed high infection in intestine (60%) rather than gills (39%) (Fig. 3a-b). The present study is in concurrence with the views of a few scientists, who predicted that endoparasites choose frequently intestine as its favorite locale due to the presence of digested food or due to its greater surface area and ectoparasites preferably choose gills as their favorite site22,62-64.
| Table 2: | Influence of seasons on parasitization of M. vittatus and M. cavasius |
| *Result is not significant at p<0.05 | |
| Table 3: | Diversity parameters and distribution patterns of parasitic species of Mystus vittatus (n=116) |
*Common: 30-50%, Frequent: 10-30%, Rare: 4-10%, Sporadic: <4%, **Core sp.: >66%, Secondary sp.: Between 66-33%, Satellite sp.: <33% |
|
| Table 4: | Diversity parameters and distribution patterns of parasitic species of Mystus cavasius (n = 94) |
*Common: 30-50%, Frequent: 10-30%, Rare: 4-10%, Sporadic: <4%, **Core sp.: >66%, Secondary sp.: Between 66-33%, Satellite sp.: <33% |
|
| Fig. 3(a-b): | Percentage of infection in different organs of M. vittatus and M. cavasius |
| Table 5: | Number of parasites obtained, dominance index and mean total parasites of different parasitic groups in M. vittatus and M. cavasius |
| Table 6: | Frequency distribution of number of parasitic groups per individual in M. vittatus and M. cavasius |
*n = 116, Σx = 3, X = 3/116 = 0.025, Range = 1-3, **n = 94, Σx = 3, X = 3/94 = 0.031, Range = 1-3 |
|
Various factors such as length of the host, age, sex, alteration in diet, in the quantity of food ingested, variation in immunological competence and changes in the possibility of contact with intermediate hosts might discriminate the prevalence and intensity of the parasite community.
Infracommunities of M. vittatus and M. cavasius: A total of 70 (60.3%) M. vittatus and 64 (68.1%) M. cavasius parasitized with at least one or more parasite species. A sum of 283 individual parasites was collected with a mean of 2 parasites/fish in M. vittatus whereas a total of 399 individual parasites were collected with a mean of 4 parasites/fish in M. cavasius. Forty-six hosts (39.6%) showed infection with one parasite species and 19 (16.3%), 4 (3.44%) and 1 (0.86%) showed multiple infections with 2, 3 and 4 parasite species, respectively in M. vittatus (Table 7). Likewise, 32 (34.04%), 22 (23.4%), 8 (8.51%), 1 (1.1%) and 1 (1.1%) M. cavasius fish depicted multiple infections with 1, 2, 3, 4 and 5 parasite species, respectively (Table 7). The lower values of Shannon’s H’ index (0.64±0.45) and Simpson index (0.16) for M. vittatus and H’index (0.75±0.54) and Simpson index (0.29) for M. cavasius indicates less diversification of parasitic community. On the other hand, the slightly higher value of Shannon based evenness (E = 0.84±0.59) for M. vittatus and (E = 0.75±0.54) for M. cavasius suggests that community structures show consistent distribution of all parasite species (Table 8). Among the eight parasites obtained from M. vittatus, H. macrones (28.44%), T. tengra (19.8%) and B. indicus (13.8%) are frequently occurring species. Similarly, R. podderi (6.89%), A. striatus (6.03%), Metacercaria I. hypselobagri (5.17%) and R. thapari (4.31%) occur rarely with prevalence ranging between 4-10% and R. godavarensis was the sporadically occurring species. While all the six parasites of M. cavasius were frequently occurring with H. macrones (28.47%) and R. podderi (19.14%) showing a high prevalence (Table 3, 4). All the nine species are satellite species and there are no core and secondary species in both the hosts. Berger-Parkers dominance index was calculated for each species of parasite in the host. The monogenea, T. tengra (37.8%) was most prevalent in the parasite community of M. vittatus but occupied the position of satellite species.
| Table 7: | Frequency distribution of number of parasitic species per individual in M. vittatus and M. cavasius |
| *n = 116, Σx = 4, X = 4/116 = 0.034, Range = 1-4, **n = 94, Σx = 5, X = 5/94 = 0.053, Range = 1-5 | |
| Table 8: | Diversity parameters of metazoan parasite communities of M. vittatus and M. cavasius |
Likewise, R. podderi (24.5%) occurred in high numbers but occupied the position of satellite species in the parasitic community of M. cavasius. Of the total 9 metazoan parasites from both the fishes 5 species i.e., H. macrones, B. indicus, T. tengra, R. podderi and R. thapari are common to both the hosts and presented a strong similarity in the species richness of both the fishes which was evidenced by a Jaccard’s similarity coefficient (SJ = 55%). The ratio of variance to mean values gave the index of dispersion (DI). All the parasites, expect R. godavarensis and A. striatus exhibited over-dispersed (aggregated) distribution in M. vittatus. Similarly, all parasites of M. cavasius exhibited over-dispersed distribution (Table 9). The aggregated distribution of the parasite population is one of the universal features of metazoan parasite infection65-67. The present study is in harmony with the views of Anderson and Gordon68 which suggested that the aggregated pattern might be due to varied behavioral changes of the host, susceptibility sand capability of host immunological response.
Infection with respect to host standard length: The relationship between host length and might be due to the incidence and association between parasite diversity and body length of sample46,69-75. According to Pearson’s correlation coefficient, a less positive correlation (r = 0.359 for M. vittatus and r = 0.395 for M. cavasius) exists between host length and parasitic abundance. Middle-aged fishes are more susceptible to parasite infection than the younger and older ones.
Infection in relation host sex: Prevalence of parasites with respect to host sex varies. Male hosts showed more infection than females71,76-78 while a few scientists were of the opinion that females are more infected than males79-81. The present study is in harmony with the views of Jarkovsky et al.82, who suggested that there are no significant differences in infection rates of male and female hosts. In the present survey of 116 M. vittatus, 51 being males, 65 being females, of which 31 (60.7%) male and 39 (60%) female fishes were infected with at least one parasite. Similarly, of the 94 M. cavasius, 48 being males and 46 being females, of which 34 (70.8%) male and 30 (65.2%) female fishes were infected with at least one parasite. The impact of host sex on the overall prevalence of infection was analyzed by Chi-square test and Mann-Whitney U-test for each host species sex wise individually. Based on a benchmark of 0.05 alpha, the estimated χ2-value = 0.0018, p = 0.966 for M. vittatus and χ2-value = 0.0648, p = 0.799 for M. cavasius suggested that there was no statistically significant association between the parasite abundance of males and females of both the fishes. The insignificant values with respect to sex from Z (U)-test for M. vittatus (Z = -0.13, p = 0.896) and for M. cavasius (Z = 0.17, p = 0.865) at p<0.05 showed that the ecological relationship of both males and females might be similar (Table 10, 11). However, individual parasitization showed consistent results which suggest that host sex has no role to play in the parasitization except Metacercaria I. hypselobagri in M. vittatus which showed infection in males.
Co-existence of two species within a same host is referred it as interspecific association. Jaccard’s index (JI) can monitor this type of association between each pair of parasite species. Hubalek83, suggested that sharing of same biotic and abiotic environments, different habitat preference and reciprocated affinity for each other might be the inspiring factors for the existence of association between different species. The above results depicted that there is very diminutive competition among species of ectoparasite and endoparasite in the host species as they share different niches within the hosts. Only, T. tengra and B. indicus (0.64) in M. vittatus and R. podderi and R. thapari (0.916) in M. cavasius showed higher values, suggesting that these parasites share a common niche i.e., gills within the host (Table 12,13).
| Table 9: | Mean (X), variance (s2) and dispersion index (s2/X) of parasite species in M. vittatus and M. cavasius |
| Table 10: | Diversity parameters of parasitic species in males and females and values of Mann-Whitney U-test to evaluate rate of host sex and parasitic abundance in Mystus vittatus |
Nm: Number of males examined, Nf: Number of females examined, Nmi: Number of males infected, Nfi: Number of females infected, Pm and Pf: Prevalence of males and females respectively, MIm and MIf: Mean intensity of males and females, MAm and MAf: Mean abundance of males and females respectively, p1, p2: Significance level |
|
| Table 11: | Diversity parameters of parasitic species in males and females and values of Mann-Whitney U-test to evaluate rate of host sex and parasitic abundance in Mystus cavasius |
Nm: Number of males examined, Nf: Number of females examined, Nmi: Number of males infected, Nfi: Number of females infected, Pm and Pf: Prevalence of males and females respectively, MIm and MIf: Mean intensity of males and females, MAm and MAf: Mean abundance of males and females respectively, p1, p2: Significance level | |
| Table 12: | Values of Jaccard’s Index (JI) to estimate interspecific association between each pair of parasite species of M. vittatus |
| Table 13: | Values of Jaccard’s index (JI) to estimate interspecific association between each pair of parasite species of M.cavasius |
Hence, the present ecological study put forward that parasitic communities of M. vittatus and M. cavasius show maximum similarity in their species composition less diverse, conventional, depauperate and non-interactive and holds good with the views of Holmes84, who suggested that freshwater counterparts are less diverse than the marine ones.
CONCLUSION
Comparative study of the parasite fauna of two fish species of the genus Mystus from the River Godavari revealed a strong similarity in their species richness. The parasitic community of M. vittatus was predominated by monogeneans followed by the digeneans whereas acanthocephalans conquered the parasitic community in M. cavasius followed by the monogeneans. The fully sampled metazoan infracommunities of both the fishes showed less but consistent diversity of parasitic species and there were no core and secondary species. Host size and sex has very less to no influence on the parasitization, respectively. All the parasites showed over-dispersed distribution patterns except A. striatus, which displayed a random distribution pattern. Only monogeneans in M. vittatus and acanthocephalans in M. cavasius showed high JI values which might be due to the sharing the common niches. Hence, the present ecological study puts forward that parasitic communities of M. vittatus and M. cavasius show maximum similarity in their species composition but are less diverse, conventional, depauperate and non-interactive.
SIGNIFICANCE STATEMENTS
This study discovers the fact that the parasitic community structure of the two freshwater fish species of the genus Mystus showed less species diversity and strong similarity of species composition compared to their marine counterparts. This study help the future researchers to analyze the parasitic community structure of other freshwater fishes.
ACKNOWLEDGMENTS
The First author, Anu prasanna Vankara is grateful to CSIR for providing the financial assistance as JRF and SRF (CSIR Award No. 9/2(467)/2004/EMR.dt.17.11.2004).