1.
Introduction
Fish
is an important source of protein to humans and other animals. Fishing
activities also offer employment opportunities to many people as well as income
at household and national level. Therefore, it can provide numerous yields to a
large number of unskilled people including women through their involvement in
fish processing activities [1].
More
than 200 species of fish are known to occur in lakes, rivers and reservoirs in
Ethiopia [2]. The country depends on its inland
water bodies for fish supply for its population. The annual fish production
potential of the country based on empirical methods on individual lake surface
area and mean depth of major water bodies was estimated to be 30.000 to 51.000
tons [3].
Lake
Ziway serves as a home for several species of fish including Oreochromis
niloticus, Tilapia zillii, Barbus species, Clarias
gariepinus and Carp species, in which some are native and others
are exotic. The exotic fish species were introduced into the Lake by the
Ministry of Agriculture with the aim of fishery development [4]. The
annual fish production potential yield of Lake Ziway was estimated between
3,000 to 6680 tons per year [5].
Freshwater
fish can serve as definitive, intermediate or paratenic (Transport) hosts in
the life cycles of many species of protozoan, metazoan and crustacean
parasites. The parasites usually affect the marketability of commercially
produced fish, thus raising a lot of public health concerns, especially in
areas where raw or smoked fish are eaten [6].
Fish
parasites are known to cause mortality both in aquaculture and inland fisheries
and some are also a cause for human diseases in many areas of the world [7]. Disease and parasites infestation of aquaculture
fish species in Africa have been poorly studied in Africa as a whole and in
sub-Saharan Africa in particular (South Africa being the exception). So,
parasites are the most prevalent problems in African fresh water [8]. Parasites of fish are of concern since they often
produce a weakening of the hosts immune system thereby increasing their
susceptibility to secondary infection by disease causing agents (e.g. fungi,
bacteria and viruses) resulting in the nutritive devaluation of fish and
subsequent economic losses [9]. In fish farming or
aquaculture, for example, some parasites may be highly deleterious for fish species
causing serious outbreaks of diseases and contribute to high fish mortalities resulting
in economic losses [10]. parasites of fishes may
cause a decrease in growth rate, weight loss, emaciation or even suppress reproductive
activity [11].
Nematodes are
common parasites in freshwater and marine fish, amphibians, reptiles and birds.
Larval stages of nematodes either occur encysted in the tissue or free in the
body cavity of fish, while the adults live in the stomach or small intestine of
piscivorous birds, notably pelicans, cormorants, herons and darters [6]. Of all the larval nematodes, the most common genus
is Contra caecum, which has a trans-African distribution and has been recorded
in both Clarias gariepinus
and Oreochromis
niloticus fish species [12]. Adult
Contra caecum species from fish-eating birds have been studied and recorded by Saayman
et al. (1991) [13]. Contra caecum species are in
genus ascaridoide, family anisakidae, and they are parasite of aquatic birds
and mammals. The larvae of contra caecum species occur in the body cavity and
mesenteries of fish while adult in gut of pscivorous birds, notably pelicans, cormorants,
herons and darters [14].
So,
the objective of this paper is
·
To assess the
prevalence of contraceacum parasite of African catfish and Nile tilapia of Lake
Ziway,
·
To identify the
risk factors for parasitic infestation and
·
To aware public
about zoonotic importance of parasite when people eat raw fish meat.
2. Material
and Methods
2.1. Study
Area
The study was
conducted on Lake Ziway which is adjacent to Batu town located in Oromia
regional state, in eastern Shoa; Adami Tulu jiddo wereda at distance of 160km
from Addis Ababa. The town is adjacent to Lake Ziway (Lake Dambal) on western
shore. The economy of town is based on fishing and horticulture. Lake Ziway is
one of the fresh water rift valleys of Ethiopia. It is 31km long and 20km wide
with surface of 440 kilometer square. It has maximum depth of 9m and elevation
of 1,636 meters above sea level. The climate of Ziway is warm and temperate.
The summer has a good deal of rain fall, while the winter has very little
rainfall. The average of annual temperature and rainfalls are 19.30c and 837mm respectively. The lake is fed primarily by two rivers, the Meki from the west and
the Katar from the east direction.
It contains five islands, including Debre Sina, Galila, Bird Island and Tulu Gudo [15].
2.2. Study Population
Ziway Lake is endowed by many native and exotic fish
species. Of these, four species of fish are commercially important. These are
African catfish, Nile tilapia, common carp and crussian carp [16]. The fish species included in the current study were Nile tilapia and
African cat fish of the Lake Ziway. From commercially important fishes, the
rest two were not included because they can resist the infestation of contra
caecum parasite. The native fish species were not included except African cat
fish and Nile tilapia because their body sizes were very small and hence, it
was not convenient to catch them during study periods. In study both sexes and
species of fishes were included.
2.3. Study
Design
A cross sectional
study was conducted from November 2016 to March 2017 at Lake Ziway to determine
and identify the prevalent contra caecum parasite on randomly selected Nile tilapia and African catfish species.
2.4. Sample
Size and Sampling Method
A simple random
sampling method was used to select study fish species. The sample sizes needed
for the study were calculated by using the formula given by Thru field (2005) [17].
n= 1.962P
(1-P)
d2
Where n= Total calculated sample size, P=
expected prevalence, d= absolute precision.
The study
considered expected prevalence of 50% for the sample size calculation, and
hence, the sample sizes were 384. But previously, the proportion of contra caecum
infestation was stated in research conducted on prevalence of internal parasite
and fish disease survey of Ziway Lake. Extra 28 species fishes were added for
purpose of precision. So, overall 412 sample sizes were selected.
2.5. Study
Methodology
All fish samples selected by lottery method were purchased
from fish seller at near of Ziway Lake. Then, the samples were transported
immediately in ice box to Ziway Fishery Research Center Laboratory. In the
laboratory, the species, sex and site of infection of the fish were identified
and recorded. The external surface of each organ was examined and postmortem
examination was done using appropriate postmortem kits using standard
evisceration technique [18]. In short, the whole
body cavity was cut opened and examined for parasite. The internal organs were
removed and placed separately in Petri dishes containing 0.75% saline solution.
The collected parasite was preserved in 70% ethanol and fixed in glycerin for
further identification. Finally, the parasite was identified under stereo
microscope using the identification guideline of Paperna (1996) [6].
2.6. Data Management and Analysis
Collected data
were summarized as proportion by descriptive statistics. Then the data analyzed
for the considered risk factors by Chi-square test, 95% CI and p-value. For the
analysis STATA 11 software will be used. For all statistical analysis, a
significant level (p-value) of less than 0.05 was considered as statistically
significant.
3. Result
In this study a
total of 412 fish samples were selected. Of these, 52 were affected by contra
caecum parasite, giving the overall prevalence of 12.62%. Out of the examined
255 Nile tilapia, 19 (7.45%) were affected by the parasite. However, from the
examined 157 African cat fish, 33 (21.01%) were affected by the parasite. The
result reveal that there was statistically significant difference (χ2=16.2208, p=0.000) in the distribution of parasite
between the two species of fish. African cat fish was found (p=0.000,
CI=0.146065-0.2743172) more association with contra caecum parasite than Nile
tilapia (Table 1).
(Table 2) Depicts the occurrence of contra
caecum parasites in male and female fish. Out of the examined 214 male fish,
23(10.75%) were infected by contra caecum parasite. On the other hand, of the
examined 198 female fish, 29(14.65%) were affected by contra caecum parasite of
fish. The occurrence of the internal parasites did not show any statistical
significant difference between male and female fish (χ2=1.4175,
p=0.234).
The genus Contra
caecum was the parasite affecting both species and sexes of fish in Lake Ziway.
The larva of parasite was observed in pericardium cavity (13.46%), intestine
(11.54%), ovary (17.3%) and caecum (17.3%). The larva of parasite also observed
on mesentery (13.46%), liver (15.38%) and heart (11.54%).
4. Discussion
The study of this
work revealed that Nile Tilapia and African cat fish were infested by contra caecum
parasite. Prevalence of parasite was higher in African cat fish (21.01%) than
Nile tilapia (7.45%). It was due to feeding behavior of African catfish.
In
fact, the African catfish is less selective or omnivorous feeding behavior [19]. This behavior of the fish could expose it for
easy transmission of parasites from invertebrate intermediate hosts and fish
intermediate hosts [20].
The prevalence of contra
caecum parasite of Nile tilapia in current study was lower than prevalence previously reported in Lake Alau (23.8%) in Nigeria [21], 39.9% in
northern Tana [22], in Lake Naivasha 85% with
mean of 9 worms per fish, in Lake Baringo 70% with 5 worms per fish and in Lake
Magadi 80% with a mean of 2 worms per fish were reported [23], in southern gulf of Lake Tana (59.77%) in
Ethiopia [24] and 39.67% at Lake Awassa [25]. Teferra (1990) [26]
on the other hand reported that, in Lake Tana 68.66% Oreochromis niloticus were found infested with larval nematode Contra caecum species. This
difference might be due to the geographical variation difference offering
suitable ecological niches for the parasite. As described by Paperna (1996) [6], the present of intermediate hosts and prevailing
physiochemical factors will affect parasitic diseases. Moreover, the hygienic
conditions and the prevailing climatologically factors may affect the
distribution of parasites. However, the prevalence parasite infestation of Nile
tilapia obtained in the current study was almost nearly similar to the
prevalence of 8.60% recorded in the previous study in the same Lake two years
ago.
The prevalence of
contra caecum parasite of Africa cat fish was also lower than the previous
report of 27.60 % at Lake Awassa in Ethiopia [27] and at
lake Lake Chivero (42.6%), Zimbabwe [10]. It
was also lower than prevalence recorded from the Hartbeespoort dam (95.3%) by Boomers
(1982) and recorded a prevalence of 46% from Lake St. Lucia [12]. Current prevalence of contra caecum infestation
of African catfish was higher than previous report from the same lake (5.33%)
in Ethiopia [28]. This increased value due to
gutting activity conducted at side of Ziway Lake that perpetuate the life cycle
of contra caecum parasite. Everything except edible fish was returned to the
lake. Fish butchers wash their hands and materials within lake. They also
expose gutted internal organs to surround birds. But the prevalence parasite
infestation of African catfish obtained in the current study was almost nearly
similar to the prevalence of 19.02% recorded in the previous study in the same
Lake two years ago.
In current study
Even though statistically no significant difference obtained relatively higher
prevalence of larvae of Contra caecum
nematode infestation was recorded in female (14.65%) than male (10.75%).This observation correspond to the findings of Imam and Dewu
(2010) [29], Bichi and Ibrahim (2009) [30] and Mhaisen et al. (1988) [31], It
was due to female fish were generally more liable than male to infestation with
nematodes, cestodes, acanthocephalan, crustacean and copepod parasites [32]. The difference in infestation rate of male and
female fish recorded in these studies could be attributed to genetic
predisposition and differential susceptibility owing to the difference of their
physiological condition. Female fish especially gravid ones are susceptible to
helminthes infestation as this physiological state could reduce the resistance
of the fish to infestation by the parasite [33,34].
5.
Conclusion
and Recommendations
The study of this
work revealed that Nile Tilapia and African cat fish were infested by contra caecum
parasite. Prevalence of parasite was higher in African cat fish than Nile
tilapia. The parasite has many hosts range including some aquatic fish, and
piscivorous birds. So, infestation of fishes by this Parasite can cause
nutritive devaluation of fish and subsequent economic losses.
Gutting activity
conducted at side of Ziway Lake was one of the factors that perpetuate the life
cycle of contra caecum parasite. Everything except edible fish was returned to
the lake. Fish butchers wash their hands and materials within lake. They also
expose gutted internal organs to surround birds. The parasite has also zoonotic
importance which human can be affected by eating raw fish meat. Based on above
conclusion the following recommendations are forwarded:
·
Constructing fish
abattoir is essential. It has numerous advantages such as: - To create job
opportunity for people, suitable for tax collection, comfortable for regulation
and to alleviate over fishing activity.
·
Appropriate
disposal of gutted organs is essential in order not expose to surrounding
birds.
·
Price gain
between fish butchers and fish sellers should be balanced. Fish sellers of
ziway town were gain more price than fish butchers. For this reason, fish
butchers were spending most of time on gutting and most of them ate a raw fish
meat.
·
Creating public
awareness about zoonotic importance of contra caecum parasite is essential in
order human not to consume raw fish meat without cooking.
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