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96
Indian Journal of Animal Sciences 80 (11): 1152–56, November 2010
Occurrence of fish louse (Argulus sp.) on Indian snow trout
(Schizothorax richardsonii) and golden mahseer (Tor putitora) in subtropical
Himalayan Lake of Bhimtal, Uttarakhand, India
SUMANTA KUMAR MALLIK1, NEETU SHAHI2, N N PANDEY3, R S HALDAR4 and AMIT PANDE5
Directorate of Coldwater Fisheries Research (DCFR), ICAR, Bhimtal, Nainital, Uttarakhand 263 136 India
Received: 16 January 2010; Accepted: 1 September 2010
ABSTRACT
Indian snow trout (Schizothorax richardsonii) and golden mahseer (Tor putitora) from cage culture unit of Bhimtal
Lake were examined for fish louse (Argulus) infestation from August 2008 to January 2009. The percentages of
S. richardsonii infected were 51.21, whereas abundance and mean intensity of infestations were 1.05 and 2.06 respectively.
Maximum prevalence (70.1%) was observed in September with least in December. Percentages of host infected in T.
putitora were 25 with abundance and mean intensity of 0.34 and 1.36 respectively. One to two percentage of fish stock
was fungal infected. Measurement of crustacean parasite illustrated carapace length (CL) comprised 75% of average
total body length (5.4 mm). Prevalence was positively correlated (S. richardsonii: r = 0.88; and T. putitora: r = 0.91)
with decrease in water temperature. The results of mean intensity of Argulus infestation indicated an initial stage of
infection in both the species. So the present study draws immediate attentions of fish health management towards
enhancement of fish production in coldwater aquatic resources of India.
Key words: Argulus, Coldwater, Fish health
The crustacean ectoparasite fish louse (Argulus), is one
of the major threats for fish health management and aquatic
crop production in fisheries in tropical and temperate regions
(Costello 1993). This crustacean parasite punctures the skin
of the hosts with modified mouthparts and feeds on blood
by releasing anticoagulants into fish (Hakalahti et al. 2004).
Thus in Argulus infestation (Aurgulosis), the chance of fish
death due to secondary infection increases. Aurgulosis
(Crustacea: Branchiura) was observed in many European
freshwater lakes and fish farm (Buchmann and Uldal 1995,
Grignard et al. 1996, and Valtonen et al. 1997). Trout and
carp stocks were severely damaged by epizootics of this
parasite (Menezes et al. 1990, Rahman 1996). Argulus
infestations have been reported round the globe (Shimura
1983, Gusev 1987, Menezes et al. 1990, Gault et al. 2002,
Hakalahti and Valtonen 2003 and Bhuiyan et al. 2008).
In India, fish louse mainly infested inland capture and
culture fisheries of cyprinids, as temperatures of these water
bodies provide optimum environment for life-cycle of
Argulus. There was report of Argulus infestation in carps
from West Bengal (Clers et al. 1992). Present study is the
first report on incidence of Argulus in cage reared Indian
snow trout (Schizothorax richardsonii) and golden mahseer
(Tor putitora) from Bhimtal Lake of Uttarakhand in India.
MATERIALS AND METHODS
Description of study site
Bhimtal lake (29°2035 N 79°3333 E) is a sub-tropical
lake, situated 4494.7 feet (1370 m) above the mean sea level,
with an area of 44 ha (Kumar et al. 2007). It is situated in
Nainital district of Uttarakhand in India. This lake is perennial
in nature and a habitat to a large variety of aquatic flora and
fauna. Bottom is muddy with high organic load.
Sample collection
Live specimens of Schizothorax richardsonii and Tor
putitora were collected from cage culture unit of Bhimtal
lake, from August 2008 to January 2009. Sampling was done
once in a month. Collected specimens were examined
externally for Argulus infestation.
Data collection
Total of 2187 numbers of S. richardsonii and 186 numbers
of T. putitora were examined during the study period. The
external surface of host (skin, fins, base of the fins and
opercula region) was examined thoroughly for presence of
Argulus. Parasites were easily seen with naked eyes and were
Present address: 1–5Scientists (1e mails: sumanta1
@rediffmail.com).
November 2010] OCCURRENCE OF FISH LOUSE AND GOLDEN MAHSEER IN HIMALAYAN LAKE 1153
97
picked from the infested host with help of a blunt forceps
and needle, and fixed in 70% ethanol for identification and
measurements. Then they were examined by light microscope
at 40X and 100X for identification. S. richardsonii stock was
divided into 2 groups (4.5–5.5 cm and > 5.5 cm in length)
depending on their size to find out the effect of host size on
prevalence, abundance and mean intensity of Argulus
infestation as per Margolis et al. (1982) and Abdus et al.
(2008). Surface water temperature of the lake at cage culture
site was measured by mercury thermometer (Accuracy
0.1°C).
Data analysis
The statistical program SPSS 15.0 for Windows was used
for Spearman rho correlation analysis.
RESULTS AND DISCUSSION
Prevalence, abundance and mean Intensity of Argulus sp.
infestation on Schizothorax richardsonii
A thorough observation of collected sample showed that,
these ectoparasites were generally attached to the base of
the fins, operculum, dorsal and ventral surface of the fish
body and caudal peduncle regions. The incidence of parasitic
attachment was maximum in the operculum and base of the
pectoral fins of the parasitized fishes. Total numbers of
S. richardsonii examined for parasite infestation were 2187.
Out of 2187 hosts, 1120 fishes were infested with Argulus
sp. The number of Argulus sp. recorded from all the infested
hosts was 2312. Prevalence (percentages of fish infested),
abundance and mean intensity (number of parasite per
infested host) were 51.21%, 1.05 and 2.06 respectively. The
mean intensity is low, which indicates that fish are of parasite
infestation at initial stage. Data on month-wise abundance
and mean intensity of Argulus infestation are shown in
Table 1.
Prevalence, abundance and mean intensity of Argulus sp.
on Tor putitora
Total number of T. putitora, examined during study period
was 186. Out of this, 47 number of host were infected with
parasite. The month-wise percentages of host infected,
abundance and mean intensity are given in Table 2, which
showed 25% of stocks were infected with Argulus sp.,
whereas mean intensity revealed initial stage of infection.
During sampling period, authors could not sample more
numbers of hosts due to sampling difficulty, which explained
a relatively small sample size of T. putitora.
Monthly patterns of prevalence of Argulus sp. on S.
richardsonii and T. putitora
Maximum prevalences of Argulus sp. on S. richardsonii
(Fig. 1; 70.1%) as well as on T putitora (Table 2; 42.2%)
were recorded in September 2008. During winter in January,
fishes of both the stocks were almost free from Argulus (Figs
2 and 3).
Argulus free hosts
The hosts (Indian snow trout and Golden Mahseer), which
did not show the infestation of Argulus sp. at the time of
sampling, were observed with presence of small patches of
grey-blue colour lesions on the skin, operculum and dorsal
surface of their body. It may be due to the irritation and tissue
Table 1. Abundance and mean intensity of Argulus infestation on S. richardsonii from August to December, 2008
Month of Total number of host Total number of Abundance Mean intensity
sampling Examined Infected parasite recorded
August 505 343 780 1.54 2.27
September 426 299 627 1.47 2.09
October 411 266 576 1.40 2.16
November 402 179 291 0.72 1.62
December 443 33 38 0.08 1.15
Total 2187 1120 2312
Table 2. Prevalence, abundance and mean intensity of Argulus infestation on T. putitora from August to December, 2008
Month of Total number of host Total number of Prevalence Abundance Mean
sampling Examined Infected parasite recorded (%) intensity
August 40 13 18 32.5 0.45 1.38
September 45 19 27 42.2 0.60 1.42
October 42 8 11 19.04 0.26 1.37
November 33 5 6 15.15 0.18 1.2
December 26 2 2 7.6 0.07 1
Total 186 47 64
1154 MALLIK ET AL. [Indian Journal of Animal Sciences 80 (11)
98
Fig 2. Decreasing trend of prevalence with decrease in water
temperature, Stock: S. richardsonii (August 2008 to January 2009). Fig 3. Decreasing trend of prevalence with decrease in water
temperature, Stock: T. putitora (August, 2008 to January, 2009).
Fig 1. Monthly (August to December 2008) prevalence (%) of
Argulus infestation on S. richardsonii from cage culture unit of
Bhimtal lake.
basis, the entire host (S. richardsonii) in one cage was
examined thoroughly; Argulus sp. were removed from the
infected host and Argulus free stock was allowed to restock
in the same cage. After 10 days the cage was lifted and
sampled again and it was found same stock heavily infested
with Argulus sp. again. It is reported that an adult Argulus
can survive without a host for up to 15 days, while a newly
hatched larva for 1 or 2 days. The life cycle of this ectoparasite
depicts a newly hatched larva actively seeks host and
continues its development on fish (Alexandre et al. 2002).
The netted cage wall forms a suitable submerged object for
egg laying, hatching and completion of life-cycle of Argulus
sp. As fishes were restocked in the same cage, as said above,
the adult Argulus sp. and newly hatched one might have re-
infested the stock.
Description of isolated Argulus sp.
In present study the collected Argulus sp. was identified
based on their external characteristics. The measurement was
based on 20 specimens. Morphometry of crustacean parasite
illustrated 5.4 mm average total length (TL), 4.1 mm carapace
length (CL), which comprised 75% of total body length, 4.0
mm carapace width (CW) and 2.1 mm abdominal length
(ABL). Yildiz and Kumantas (2002) reported that total body
length of Argulus foliaceus ranged from 6 mm to 7 mm,
whereas Argulus japanicus and Argulus coregoni are from 4
mm to 8 mm and 12 mm respectively. Tam et al. (2005)
reported 5.5 mm average body length, 3.03 mm average
length of carapace (53% of overall body length), 2.9 mm of
average width of carapace and 2.1 mm of average length of
abdomen in male Argulus personatus (measurement based
on 8 male specimens of Argulus personatus). In female
Argulus personatus, the total body length, carapace length,
carapace with and abdomen were 5.6 mm, 3.7 mm, 3.4 mm
and 1.5 mm respectively (measurement based on 1 female
damage by detached parasites, which left the host with small
patches of grey-blue and lesions on their body. Alexandre et
al. (2002) reported that once the mating is over on fish body,
the female Argulus swims away from hosts and lays eggs on
plants, stones, nets and other submerged objects. So, it may
form one of the reasons why observed fish were left with
small patches of grey-blue and lesions. One to two percentage
of total stock was also found infected with cottony wool like
appearance on base of the dorsal, pelvic and caudal fins,
which most likely a fungal disease. This infestation of Argulus
sp. may be the possible cause of the secondary infection such
as fungal diseases. The attachment of Argulus paves the way
for entry of opportunistic pathogens (Ravichandran et al.
2001 and Alexandre et al. 2002). Mortality of the fishes was
not observed during sampling. Fish infected with cotton wool
like growth, were sampled and brought to laboratory for
identification of fungi. With application of hemp-seed method
(Pottinger and Day 1999, Sati and Mer 1989) it was found to
be Saprolegnia sp., which caused this secondary infection
(cottony-wool like growth) on fish body. On experimental
November 2010] OCCURRENCE OF FISH LOUSE AND GOLDEN MAHSEER IN HIMALAYAN LAKE 1155
99
specimen of Argulus personatus). Wadeh et al. (2007)
observed total body length ranged from 4.9 mm to 8.2 mm
with an average of 6.5 mm and abdomen length 1.2 mm to
1.7 mm with an average of 1.4 mm in adult female Argulus
japanicus Thiele 1900 (Crustacea: Branchiura) collected from
Shunde of Guangdong, China. They have also reported
average total body length 3.6 mm of male Argulus japanicus
Thiele, with carapace length comprising 75% of total body
length.
Effect of host size on prevalence, abundance and mean
intensity of Argulus infestation on Indian snowtrout
In present study, prevalence, abundance and mean
intensity of Argulus infestation did not vary significantly
between fish size groups in length (Stock: S richardsonii,
Table: 3). The apparent result indicated infected hosts in size
class 45 to 55 mm acquired more Argulus (mean intensity
2.14) as compared to size class > 55 mm (mean intensity
1.87). Poulin (1999) demonstrated prevalence and mean
intensity correlate positively with host body size for copepod
ectoparasite. Grutter (1994) also found a positive correlation
between host fish length and gnathiid parasite loads.
According to island biogeography theory (MacArthur and
Wilson 1967), larger hosts are likely to harbour more parasite
species and higher number of individual parasites than
smaller host. The fact that parasites attached to body surface
of larger host may mean that they provide greater surface
area and are attacked more often than smaller host (Cochran
1985). Clers et al. (1992) also recorded the similar
observation of increase abundance of Argulus infestation with
increase in host size, but the observation recorded in the study
for effect of host size group on prevalence, abundance and
mean intensity did not concur with the reports stated above.
As fishes were stocked in cage net and reared in a confined
environment, which hardly allow them flee to open water,
the parasites might have easily accessed the stock for
infestation irrespective of size of the hosts. The effect of host
size on prevalence, abundance and mean intensity of Argulus
infestation was not studied in Golden mahseer, T. putitora
because of a relatively small sample size of the fish.
Effect of water temperature on percentage of host infected
(stock: S. richardsonii and T. putitora)
The effects of water temperature on prevalence showed
positive correlation (Fig.2; S. richardsonii: r = 0.88; Fig. 3,
T. putitora: r = 0.91) in the observation. The maximum
prevalence for both fishes (S. richardsonii 70.1% and T.
putitora 42.2%) was monitored in September. Then a
decrease in percentage of host infection from October
onwards was recorded with fall of water temperature in the
present study. As optimum water temperature for completion
of Argulus life-cycle ranges between 18 and 22°C, lessen in
prevalence in November and December may be the due to
unfavorable water temperature during the said months. The
whole life cycle may take 30–100 days depending on the
water temperature of the rearing unit. So eggs can over-winter
and hatch later when water temperature starts increasing
(Alexandre et al. 2002). Clers et al. (1992) also observed
that high water temperature promotes the increase in Argulus
population.
There is marked deterioration of water quality of Bhimtal
lake with recession of its margin and shallowing in the past
few years by anthropogenic activities. There is also a marked
decrease in depth of the lake during summer with increase
in water temperature, appearance of aquatic weed infestation
and muddy fauna. All these may be the basis for infestation
of Argulus sp. on coldwater fish in cage culture system. The
present infestation of Argulus sp. may be at initial stage, but
it can be categorized in high-risk group, where organism is
termed as typically pathogenic and requires immediate
treatment and mechanical removal. Because this crustaceans
infestation not only retards the growth of the fish, but also
acts as a vector for entry of certain fish viruses (Clers et al.
1992) and secondary infections such as bacterial and fungal
diseases. Lester and Roubal (1995) also reported that growing
Argulus sp. juveniles may expose fish to fungal and bacterial
infections by irritating the skin that can affect the fish’s
feeding habit, which results in retarding growth and
sometimes death of the host. Thus a periodical monitoring
program on fish health is considered necessary to keep the
stock in healthy state. The present study sensitized us to
examine the fish culture tank at higher altitude raceways
culture system. The Indian snowtrout and Rainbow trout
stock at coldwater fish farm, Champawat, which is situated
at 5688.97 feet (1734 m) above the sea level, were examined
for Argulosis. But the stocks did not show any sign of Argulus
infestation. During sampling period, the average water
temperature of Champawat fish farm was 11.5 °C.
Virtually no extensive survey of parasites in coldwater
aquatic resources of mid-Himalayan region of India has been
done so far. As there is no information on distribution and
abundance of Argulus infestation in coldwater bodies of India,
this occurrence of Argulus sp. on coldwater fishes, Indian
snowtrout and critically endangered Golden mahseer in cage
Table 3. Prevalence, abundance and mean intensity of Argulus infection on S. richardsonii in different length group
Size group No. of No. of Number of Prevalence Abundance Mean
(length in mm) host examined host infested parasite recorded (%) intensity
45–55 459 227 486 49.45 1.05 2.14
>55 312 151 283 48.39 0.90 1. 87
1156 MALLIK ET AL. [Indian Journal of Animal Sciences 80 (11)
100
culture unit of Bhimtal Lake draws immediate attentions of
fish health management and extensive survey of parasites
towards enhancement of fish production in coldwater aquatic
resources of hilly states of India.
ACKNOWLEDGEMENTS
We are thankful to Dr P C Mahanta, Director, Directorate
of Coldwater Fisheries Research (DCFR), Bhimtal,
Uttarakhand for providing necessary support for the study
under institutional project “Coldwater Fish Health
Management”.
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