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Research Article
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Multifactorial Etiology of Infections by Larvae of Eustrongylides tubifex (Nematoda:Dioctophymidae) in Silver Whiting of the Central West Coast of India at Goa |
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Neeshma Jaiswal,
Sushil K. Upadhyay,
Anshu Malhotra
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Sandeep K. Malhotra
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ABSTRACT
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The investigations on ecological dynamics of larvae of Eustrongylides tubifex in silver whiting, Sillago sihama were conducted at the Central West Coast of India at Goa during 2008-2010.The fish were borrowed from commercial vessels and trawlers as well as purchased from market for the parasitological investigations. All the hosts were brought to laboratory, separated sexwise, freshly weighed, their total length and standard length measured. Viscera of the hosts were teased and carefully examined for helminthes parasites. The collected worms were processed for the morphometric analysis to establish indentify of worms. The dynamics of E. tubifex larvae was monitored and impact of environmental parameters established by the application of Principal Component Analysis using SYSTAT 11 software. The dominant 1st component (PCIp) of Principal Component Analysis elucidated critical negative impact (-0.560) of alkalinity of water on mean intensity of nemic populations in female fish, while the temperature optimum was 28°C, besides influence of seasonality depicting highest peak of infection prevalence in winter and the other lower peak during summer period. The appropriateness of Principal Component Analysis could be substantiated by the cumulative percentage of variance explained by Sillago sihama- E. tubifex model that could be used as post-hoc measure. Further, the stability of cumulative percentage in this study, which progressed from 28.190 to 30.167%, suggested that the model became more relevant each year. The robustness of the applications within Principal Component Analysis are strengthened in this study by the availability of two years samples under natural conditions in an aquatic ecosystem. The higher expression variability of certain select physico-chemical characteristics like, alkalinity, hardness, DO and water temperature were marked out by application of Principal Component Analysis. It also highlighted the reliability of correlation matrix as compared to covariance matrix because of ordered variability structure.
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How
to cite this article:
Neeshma Jaiswal, Sushil K. Upadhyay, Anshu Malhotra and Sandeep K. Malhotra, 2013. Multifactorial Etiology of Infections by Larvae of Eustrongylides tubifex (Nematoda:Dioctophymidae) in Silver Whiting of the Central West Coast of India at Goa. Asian Journal of Biological Sciences, 6: 21-39. DOI: 10.17311/ajbs.2013.21.39 URL: https://scialert.net/abstract/?doi=ajbs.2013.21.39
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Received: July 18, 2012;
Accepted: February 28, 2013;
Published: April 13, 2013
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INTRODUCTION
The dynamics of roundworm infrapopulations in fish of marine water bodies world
over, are under the interactive influence of a variety of hydrobiological attributes
but the intrinsic changes therein are most misunderstood, that have gained significance
in view of the recurrent climate change world over (Hudson
et al., 2006). The larvae of Eustrongylides are known to inhabit
various sites within the host fish, most frequently in the encysted form and
these worms usually mature in the interior of birds and mammals in the ambient
environment. The developmental dynamics of nematodes is under the influence
of salinity because of its direct impact on development and survival of the
nematodes in the water body (Kirk et al., 2000;
Fazio et al., 2008). Poisson distribution is
an appropriate tool to assess overdispersion of parasites within host populations
(Anderson, 1991), that ultimately assisted in estimation
of regulatory role of parasite burden on the survival of fish hosts. Parasite
have also been considered responsible to affect a wide variety of morphological
traits of the hosts (Moore, 2002) and pattern of consumption
of specific dietary items (Lindenfros et al., 2007),
which, in turn could easily influence the seasonality of infestation in fish
and other vertebrates. Despite the agreement among parasitologists on the nature
of serious effect of parasites on the biology of their hosts, an accurate identification
of traits that might be critical, could not be made mainly because of our lack
of understanding to substantiate precise influence of individual ecological
parameters in Asian waters, on specific host-parasite interrelationships. The
present investigation is a two years study to make an attempt to substantiate
affinity of environmental characteristics with host and parasite biology, by
using most modern biostatistical tools, in terms of dynamics of nematode infections
in a marine fish.
MATERIALS AND METHODS
The investigations were conducted for two consecutive years between July, 2008
to June, 2010 on marine fish Sillago sihama (N = 653) sampled at Cacra
beach at the Central West Coast of India. The collected hosts were brought to
laboratory, separated sex wise, freshly weighed and their total and standard
length were measured. The larval forms of E. tubifex (N = 2536) were
recovered in membranous cover attached to the visceral organs in body cavity
of the fish. The larvae were also encountered in the intestine as well as embedded
in cystic form in the outer wall of stomach. The cysts were then teased with
fine dissecting needles to extract the nematode larvae. The larvae were washed
in normal saline (0.85%); fixed in hot alcohol and glycerol (95:5 v/v), cleared
in lactophenol after (Malhotra and Rautela, 1984) and
mounted in glycerine.
The weekly quantitative estimation of dissolved oxygen in water was done by
the modified Winklers method (Strickland and Parsons,
1968) and water temperature recorded at the site of investigation. Water
samples were collected simultaneously in Torsons sampling bottles for
hydrobiological analyses of other parameters viz. hardness, acidity, alkalinity
and chloride by titrimetric methods after American Public Health Association
(APHA, 1998), while salinity was estimated using digital
Salinometer (ERMA hand Refractometer, Tokyo, Japan).
The correlation of Infection Prevalence (IP) and Mean Intensity (MI) with various
biological attributes of the fish as well as hydrobiological parameters were
worked out by using SYSTAT-11 software. Simultaneously, various biostatistical
parameters such as Linear regression trends, Principal Component Analysis, ANOVA
(one way), Multivariate analysis, Student t test and Mann-Whitneys
test were also worked out by using advanced biostatistical tools. The dispersion
of infection in the marine hosts was calculated by Poisson distribution.
RESULTS
Season and sex of fish: The seasonal abundance of larvae of E. tubifex
in S. sihama indicated typical single peak for mean intensity (20.0)
with infection prevalence, 90.91% during 2008-2009 and mean intensity 18.5 with
nemic prevalence 83.33% during 2009-2010 was reported in winter period. But
a second peak was also encountered in summer period (May-June) of 2008-2009
(15.2) and during 2009-2010 (14.5) (Table 1). Out of the total
examined hosts, 21.43-90.91% male fish with mean intensity 2.0-20.0 and 27.27-75.0%
female fish with mean intensity 2.29-15.20 were encountered during 2008-2009.
However, 25.0-83.33% nemic prevalence with mean intensity, 2.6-18.5 occurred
in male fish, and infection prevalence 10.0-70.0% with nemic intensity, 4.2-20.0
occurred in female fish during 2009-2010. The distribution of infection exhibited
poor agreement with Poisson series (p<0.20, Table 2). Therefore,
the nematode populations were over dispersed. The results would thus illustrate
restricted distribution of parasitic stages in certain select hosts but the
infection would not be spread in fishes all over the water body. The influence
of marine habitat characteristics, geographical location and individual physiological
state of the host fish have, therefore, predominantly influenced the distribution
pattern of these nemic larvae as one of the important factors of multifactorial
etiology highlighted in these investigations.
Hydrobiological attributes: The varied trends of infectivity by nematodes
are the order of interactive influence of physico-chemical parameters in a water
body. Therefore, no single parameter of infection, whether nemic prevalence
or mean intensity, is under the influence of a single environmental parameter.
Table 1: |
Monthwise distribution data of larvae of Eustrongylides
tubifex in Sillago sihama during 2008-2010 |
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Table 2: |
Poisson series of larvae of Eustrongylides tubifex
in Sillago sihama during 2008-2010 |
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*p<0.20(Significant) |
In the current study, the infestation by larvae in female fish inclined during
2008-2009, at higher salinity (Fig. 1) and the augmented degree
of incline between 34-35.5 mg L-1 influenced the overall incline
under salinity effect. However, the mean intensity decreased at higher alkalinity
(Fig. 2) during 2008-2009 and the effect was particularly
prominent due to effect of alkalinity at >350 mg L-1. The nemic
prevalence (Fig. 3) and mean intensity (Fig.
4) in male S. sihama declined at corresponding increase in hardness
of water during 2009-2010, that was predominantly marked at >6000 mg L-1.
The mean intensity of worms in female fish increased at enhanced water temperature
(Fig. 5) during 2008-2009.
Mann-whitneys test: The findings on nemic infection prevalence
and mean intensity in S. sihama by non-parametric Mann-Whitney Test confirmed
influence of salinity and Dissolved Oxygen during 2008-2010 as depicted in Appendix
1.
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Fig. 1: |
Correlation of mean intensity by larvae of Eustrongylides
tubifex in female Sillago sihama with salinity (ppt), during
2008-2009 |
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Fig. 2: |
Correlation of mean intensity by larvae of Eustrongylides
tubifex in female Sillago sihama alkalinity (mg L-1),
during 2008-2009 |
Multivariate analysis: The effect of salinity was predominantly marked on infection prevalence and mean intensity in both the sexes during both years of investigations, except in female fish, where influence of water temperature showed predominant effect over salinity vis-α-vis mean intensity as depicted by the multivariate analysis given below:
2008-2009
IPMALE- |
r = 0.838 |
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Tempsalinitydohardnessalkalinityaciditychloride |
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Y=-289.800-4.528X1+15.956X2+1.03X3-0.004X4-0.168X5-2.000X6-0.000X7 |
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Fig. 3: |
Correlation of infection prevalence by larvae of Eustrongylides
tubifex in male Sillago sihama hardness (mg L-1),
during 2009-2010 |
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Fig. 4: |
Correlation of mean intensity by larvae of Eustrongylides
tubifex in male Sillago sihama hardness (mg L-1),
during 2009-2010 |
IPFEMALE- |
r = 0.809 |
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TempSalinityDOHardnessAlkalinityAcidityChloride |
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Y=-69.594-11.304X1+13.183X2+5.403X3+0.003X4-0.107X5-4.455X6+0.001X7 |
MIMALE- |
r = 0.801 |
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TempSalinityDOHardnessAlkalinityAcidityChloride |
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Y=-14.336-0.878X1+2.450X2-1.006X3-0.001X4-0.057X5-0.906X6-0.000X7 |
MIFEMALE- |
r = 0.741 |
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TempSalinityDOHardnessAlkalinityAcidityChloride |
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Y=-113.063-0.632X1+4.300X2+0.156X3+0.001X4-0.039X5-0.377X6-0.000X7 |
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Fig. 5: |
Correlation of mean intensity by larvae of Eustrongylides
tubifex in female Sillago sihama with water temperature (°C),
during 2008-2009 |
2009-2010
IPMALE- r = 0.858 |
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TempSalinityDOHardnessAlkalinityAcidityChloride |
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Y=183.660+4.013X1-3.081X2-1.189X3-0.016X4-0.113X5+0.534X6-0.002X7 |
IPFEMALE- r = 0.750
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TempSalinityDOHardnessAlkalinityAcidityChloride |
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Y=389.944+5.698X1-13.079X2+8.359X3-0.011X4-0.059X5-1.718X6-0.000X7 |
MIMALE- r = 0.663 |
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TempSalinityDOHardnessAlkalinityAcidityChloride |
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Y=98.861-0.513X1-2.668X2+1.405X3-0.002X4-0.014X5+1.292X6+0.000X7 |
MIFEMALE- r = 0.812 |
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TempSalinityDOHardnessAlkalinityAcidityChloride |
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Y=-27.821+2.622X1+0.167X2-0.352X3-0.000X4-0.193X5+1.762X6-0.000X7 |
where, Temp: Water temperature; DO: Dissolved Oxygen |
Pearsonss correlation matrix: The influence of water temperature (-0.529) on infection prevalence in female; salinity (0.502) on mean intensity in female; hardness (-0.567) on infection prevalence in male and alkalinity (-0.551) on mean intensity in male were significant during 2008-2009 (Table 3). However, the negative influence of hardness (0.506) on infection prevalence in female fish by larvae of E. tubifex was recorded during 2009-2010 (Table 4). Principal component analysis: The biostatistical assessment of the impact of pollution related parameters, like enhanced salinity was substantiated by the application of Principal Component Analysis and positive coefficient value (0.528) representing mean intensity in female fish (2008-2009)(Table 5).
Table 3: |
Pearson correlation matrix interrelationship of hydrobiological
factors of larvae of Eustrongylides tubifex in Sillago sihama
during 2008-2009 |
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°C: Water temperature, DO: Dissolved oxygen, IP: Infection
prevalence, MI: Mean intensity |
Table 4: |
Pearson correlation matrix interrelationship of hydrobiological
factors of larvae of Eustrongylides tubifex in Sillago sihama
during 2009-2010. |
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°C: Water temperature, DO: Dissolved oxygen, IP: Infection
prevalence, MI: Mean intensity |
The higher expression variability of certain select physico-chemical characteristics like, alkalinity, hardness, DO and water temperature were marked out by application of PCA. It also highlighted the reliability of correlation matrix as compared to covariance matrix because of ordered variability structure, particularly its highest coefficient value (0.886) at enhanced alkalinity (2008-2009). On the other hand, declining effect of hardness (Coefficient value, -0.869) on mean intensity of roundworms in male fish (0.750) during 2009-2010 (Table 6) highlighted the significant principal inorganic ion components as salinity, alkalinity and hardness in parasitological analysis of E. tubifex infections in silver whiting in India. The Scree plots in Fig. 6 and factor loadings in Fig. 7 illustrated dominant effect of the 1st component during 2008-2009, and that of the 1st Component during 2009-2010 is depicted by Scree plots (Fig. 8) and factor loadings (Fig. 9). The inherent variance in the data of distribution of the nematode, E. tubifex in Silver whiting was illustrated by the ordered arrangement of Principal Components, that were assigned a specific number label by decreasing order of its contribution to the inherently compiled variance. A Scree plot thus generated exhibited an elbow down the abscissa, that marked point of separation of the most effective Principal Component segregated from other Principal Components, whose effects were representedly masked biostatistically, under the predominant effect of the dominant one.
Table 5: |
Magnitude of pattern of PC1P coefficient
for sexwise infection by larvae of Eustrongylides tubifex in Sillago
sihama during 2008-2009 |
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Table 6: |
Magnitude of pattern of PC1P coefficient
for sexwise infection by larvae of Eustrongylides tubifex in Sillago
sihama during 2009-2010 |
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Fig. 7: |
Factor loadings plot of infection parameters by larvae of
Eustrongylides tubifex in Sillago sihama during 2008-2009 |
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Fig. 9: |
Factor loadings plot of infection parameters by larvae of
Eustrongylides tubifex in Sillago sihama during 2009-2010 |
Therefore, the Scree plot projected restricted number of PCS in the predominant condition under natural environment, as against their contribution to mask the effect of other subsidiary ones in effect. In interpretation, the eigenvalues <0.1 are usually not very helpful in statistical terms to derive any conclusions on pattern of distribution of nematodes vis-α-vis factors of the hydrological environment. However, the Principal Components with higher eigenvalues occupied a higher location on the Scree plot and the Factor Loadings plot. The decreasing fractions of total variance explained helped to assort Principal Components displayed in decreasing order on X axis of the Scree Plot. The elbow commenced at PC3 (Started at PC3 and was distinctly noticeable at PC5 onwards till PC11) (Fig. 6 for 2008-2009 and Fig. 8 for 2009-2010), thus outlining noticeable effect of the 1st and 2nd Principal Component. Simultaneously, the non-significant influence of PC3 onwards, till PC11 was marked.
The robustness of the applications within Principal Component Analysis are
strengthened in this study by the availability of two years samples under
natural conditions in an aquatic ecosystem. Pedhazur and
Schmelkin (1991) postulated that, as a rule of thumb, 50% of the variance
should be explained by the first two or three components, to which very closer
results were computed in these investigations. In such manner, the appropriateness
of Principal Component Analysis could be substantiated by the cumulative percentage
of variance explained by this model which could be used as post-hoc measure.
Further, the stability of cumulative percentage in this study, which progressed
from 28.190 to 30.167%, suggested that the model became more relevant each year.
With all 4 indicators of infection prevalence and mean intensity loading significantly,
on the first factor during the two years (2008-09: IP male- 0.701, MI male-
0.838, MI female, 0.886; 2009-2010: IP female- 0.665, MI male- 0.752, MI female-
0.595), its strength and general character seem confirmed. In addition, the
first factor loadings for alkalinity (-0.560), hardness (-0.869) and salinity
(-0.528) also supported the strength of conclusive outcome of the study, that
have already been documented in the foregoing text (Fig. 6,
8; Table 5 for 2008-2009 and Fig.
7, 9; Table 6 for 2009-2010).
DISCUSSION
Season and sex of fish: The sustained infection peaks were encountered
in late autumn to winter period in female as well as during winter in male (OSullivan
et al., 1984; Montgomery and Montgomery, 1988).
Simultaneously, appreciably higher level of infection throughout the year illustrated
that this was due to the continuous availability of annelid intermediate hosts
for continuous occurrence of larvae of E. tubifex during most part of
the year, that further increased during late autumn to winter period. This was
in consonance with the studies of Kennedy and Fitch (1990)
and Gollock et al. (2005). There was single peak
of mean intensity in both the sexes of S. sihama during winter, as was
also concluded by Gollety et al. (2005). However,
a second peak was also observed in summer (May-June) period (Salvati
et al., 2002; Cattadori et al., 2005;
Loot et al., 2007), though such a phenomenon
was not influenced only due to the season and sex, but also by some other extrinsic
factors. A demographic pattern of parasite populations could be concluded in
which dynamics of populations interacted with spatial and temporal variations
in the environment (Anderson and Gordon, 1982; Nee
et al., 1991). The voracious host feeding habits and local habitat
characteristics, availability of appropriate intermediate hosts, niche, size
of population, spatial features of habitats were suggested as some of the main
factors contributing to the variability observed in community composition and
richness by earlier workers (Martinez-Aquino et al.,
2007).
There was higher infection in female fish than males in 2008-2009, as the report
of Pence and Meinzer (1979) also found that the prevalence
of Taenia leonine was significantly higher in female than males in west
Texas. It was due to the positive interaction between endocrine and immune parameters
that females harboured lower levels of infection and infestation than male fish
during the current investigations. Such factors could contribute to the immune
systems of carp being more effective during spawning season (Saha
et al., 2002). Therefore, female fish were more immunized due to
higher level of cortisol (F), a major glucocorticoid, which often increased
in the plasma of the spawning fish (Schmidt and Idler, 1962;
Wingfield and Grimm, 1977; Maule
et al., 1996). So, the female fish was more healthy and resistant
for the helminthes infection than that of the male fish.
One major finding on Poisson series was that parasite assemblages were not
the result of random processes (p<0.20), but rather the result of the interplay
among geographical location, habitat characteristics and host identity (Kennedy
and Hartvigsen, 2000; Nelson and Dick, 2002; Calvete
et al., 2004). It was demonstrated by Krasnov
et al. (2008) that the external environmental influence critically
determined the extent and variety of invasion by helminth parasites, because
of its initial influence on host populations, while the frequent recurrence
of parasitic communities depended, in turn, on the effect of hosts physiological
response to parasitic invasion.
Hydrobiological parameters: The regulatory influence of Dissolved oxygen
of marine water body on mean intensity by larvae of E. tubifex in male
(Y = 20.74-1.96 X; r = -0.50, p<0.40) and female fish (Y = 16.42-1.60 X;
r = -0.50, p<0.50) was very well marked and showed negative association during
2008-2009. These findings were supported by the conclusions of Zargar
et al. (2011) on Diplozoon kashmirensis. However, the pattern
of nemic prevalence in female fish during 2009-2010 was dependent of the effect
of Dissolved oxygen (Kuris et al., 1980).
The available literature also supported that the frequency of infection was
greater due to the temperate regions having served as the most suitable habitat
for parasitizes carp (Brock, 1983). But, simultaneously,
the establishment of developmental stages resulted in increase of mean intensity
in female fish at augmented water temperature (Y = 24.22+1.12 X; r = 0.50, p<0.40;
Fig. 5) during 2008-2009. Kovskii and
Khudolei (1989) concluded from their study a direct relation in temperature
and parasitic infection, exhibiting positive association between the two. These
observations were in agreement with the work reported herein, as the rate of
infection increased with increase in temperature. It was also emphasized by
Chubb (1980) and Ernst et al.
(2005) that temperature increased the growth period of parasites and shortened
the generation time. Under these conditions, the parasites were in a position
to complete their life cycle rapidly. The enhanced temperature could not support
the infection prevalence in female fish, because the lymphocyte count in plasma
of fish increased at the higher temperature in female fish with simultaneous
increase in the cortisol level, that was responsible for the immunity of fish
against the nemic infection (Saha et al., 2002).
The augmentation in salinity supported the increase in mean intensity in female
S. sihama (Fig. 1) during 2008-2009. This finding derived
support from the contention of Dogiel et al. (1961),
Snieszko (1974), Chubb (1980),
Beer and German (1993), Kennedy and
Watt (1994), Marcogliese (2001) and Lafferty
and Kuris (2005) that anthropogenic activities were responsible for the
eutrophication and thus provided favourable conditions for the emergence of
more annelids larvae as intermediate hosts for larvae of E. tubifex.
Therefore, the voracious feeding of S. sihama during that period was
apparently responsible for the greater prevalence of infection. No effect of
acidity and chloride on the infection prevalence and mean intensity was concluded
in the two years studies.
The multivariate analysis illustrated that salinity masked the effect of other hydrobiological parameters and had significant association with infection prevalence in male (r = 0.838) and female (r = 0.809) as well as with mean intensity in male (r = 0.801) and female (r = 0.741) during 2008-2009. However, water temperature co-ordinated with influence of salinity to mask the impact of other hydrobiological factors on the infection prevalence in male (r = 0.858) and mean intensity in female (r = 0.812). However, significant masking influence of Dissolved oxygen on infection prevalence in female (r = 0.750) and salinity on mean intensity in male S. sihama (r = 0.663) was noticed on the other physico-chemical factors during 2009-2010. The principle advantage of application of principle component analysis was to provide an insight to explain variability that was an outcome of a gamut of interactions between host-parasite and hydrological environment. PCA facilitated to mask singularity and thus exposed multiplex of directions of variability operative within an aquatic ecosystem to support fish-E. tubifex interactions at the differential level under the combined influence of a variety of hydrobiological attributes opearating at the same point of time and in several directions to effectuate different dimensions. The higher expression variability of certain select physico-chemical characteristics like, alkalinity, hardness, DO and water temperature were marked out by application of PCA. It also highlighted the reliability of correlation matrix as compared to covariance matrix because of ordered variability structure.
Principal component analysis: The dominant 1st component (PC1p)
could be deduced from the scree plot of Principal Component Analysis of monthwise
response of infection data by E. tubifex in S. sihama during 2008-2009
(Fig. 6; Table 5) and 2009-2010 (Fig.
8; Table 4.) as well as factor loadings plot during 2008-2009
(Fig. 7) and 2009-2010 (Fig. 9). The influence
of alkalinity (-0.560) had a critical impact on the oscillations in monthly
and seasonal cycles of nemic mean intensity in female fish (0.886; Table
5). Identical evidence emerged from linear regression analysis between nemic
mean intensity in female fish vis-α-vis alkalinity (Y = 13.95-0.02
X, r = 0.50, p<0.05, F1,10 = 1.642, S0.250; Fig.
2). The indirect discriminatory attributes of the hydrological environment
like alkalinity, that contributed to a variety of structural inequalities (Wrench,
2007), by their neutral actions, influenced the action of direct discriminatory
factors of hormonal intereference by the female sex. These findings were supported
by the earlier studies of Engelbrecht (1958) on Eustrongylid
infections in fishes of reservoirs of thermal power plants and by Malhotra
and Banerjee (1990) on plerocercoid infections in the fishes of Indian Gangetic
plains reporting significant decline at increased alkalinity. The analysis of
targeted mechanism with an outreach into the step by step operations
of an aggregated group of environmental factors, as well as the mechanism
of their initiation i.e., trigger has been approached by putting
into statistical test, the data generated from naturally occurring interactions
within the host-parasite system that is a part of a specific ecosystem, for
instance, aquatic ecosystem in the current investigations. The outcome is particularly
significant because the data might otherwise seem to be with potentially non-discriminatory,
yet the interactive resultant effect could reveal meaningful exclusionary and
inclusionary dimensions. The study provided an opportunity to understand that
among a voluminous data on environmental sets being available, a select few
attributes could eventually be active to influence the pathway of a particular
parasite, E. tubifex, in this case. In the similar fashion, the association
of salinity (0.528) with mean intensity in female fish hosts could be explained
by 28.190% total explained variance, as also confirmed by the significance obtained
(r = 0.741) with multivariate analysis and linear regression trend (Y = 89.67+2.75
X, r = 0.50, p<0.50, F1,10 = 3.377, S0.100 Fig.
1) during 2008-2009. Pearson correlation matrix also exhibited high significance
(0.502) with salinity during 2008-2009 (Table 3). In the following
year, 2009-2010, Principal Component Analysis of infection variables of mean
intensity by nematode larvae in male fish (0.750) under influence of hardness
of riverine water (-0.869; Table 6) showed a first component
(PC1p) accounting for 30.167% (Fig. 7, 8).
This was in conformity to the finding of significant linear regression trend
between hardness and nemic intensity in male fish (Fig. 4).
The declining influence of hardness on the mean nemic intensity (Y = 17.53-0.002
X, r = -0.50, p<0.025, F1,10 = 3.023 S0.250; Pearson
correlation matrix, -0.482; Fig. 4) and infection prevalence
in male fish (Y = 129.32-0.02 X, r = -0.82, p<0.40, F1,10 = 22.201,
S0.005; Pearson correlation matrix, -0.830; Fig. 3)
during 2009-2010 were also noticeable. Therefore, the biostatistical correlations
worked out in the current investigation highlighted the relatively significant
influence of salinity, alkalinity, hardness and Dissolved oxygen as well as
water temperature in the dynamics of infrapopulations of E. tubifex infections
in marine fish, S. sihama at the Central West Coast of India at Goa.
Navara (2009) attributed such influence to the resource
availability and consumer density differentiation pattern due to the effect
of latitudinal variation in climatic factors between temperate and tropical
regions. Therefore, the study based on the analysis of environmental data related
to a host fish-E. tubifex infections provided evidence of the existing
constituents of structural inequalities in natural water body, comprising alkalinity,
hardness, salinity, dissolved oxygen and water temperature, having triggered
larval growth following patterns, that were demonstrated herein, and predominantly
thus, these structural inequalities affected the role of direct discriminators
of host biology that deduced specific nemic pathways concluded in these investigations.
ACKNOWLEDGMENTS NJ acknowledges the award of Post-Doctoral Fellowship from the University Grants Commission, Govt. of India. SKU is thankful to Department of Biotechnology, Govt. of India for a research fellowship under grant no. BT/PR9651/SPD/09/818/2007. APPENDIX
APPENDIX 1 |
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