Health Condition of a Farmed Tilapia (Oreochromis niloticus) in Earthen
Ponds, Northern Bangladesh
M. Belal Hossain
Investigation on health conditions of a farmed tilapia (Oreochromis niloticus) in two upazilas of Mymensingh District were carried out through clinical and histopathological observation during September, 2010 to March, 2011. Fish sample and water quality parameters (temperature, dissolved oxygen, pH, alkalinity, nitrite and ammonia) were monitored on a monthly basis. Clinical observations of the fish were also done for any kind of abnormalities at monthly intervals. Samples of skin, muscle, liver and kidney were observed by histological techniques. Among the water quality factors, water temperature and alkalinity were found at unfavourable level for fish during the colder months. Clinically, it was observed that the tilapia were more affected from December and January and almost normal in appearance during September, October, November and March. Different clinical symptoms like rough skin, scale loss, red spots and dermal lesions were noticed in December and January. Histopathologically, sampled fish were found almost normal in the months of September and October. In the month of November minor pathologies were found to be started. Marked pathological changes like necrosis, pyknosis, hemorrhage, hypertrophy, hyperplasia, missing of primary and secondary gill lamellae, vacuums, fat droplets and fungal granuloma and fungal hyphae were observed in fish organs during December and January. Whereas, the pathological condition of fish gradually reduced in February. Again when considered individual fish pond, fishes of pond 1 (P1) in Bhaluka upazila were more affected than other ponds. The study showed that severity of clinical and pathological changes were increased in December and January. During the period of Epizootic Ulcerative Syndrome (EUS), bacterial and protozoan diseases were evident.
Received: May 04, 2012;
Accepted: July 18, 2012;
Published: September 06, 2012
The introduction of tilapia in Bangladesh from Thailand was first initiated
in 1954 with Tilapia mossambicus and later in 1974, high yielding species
of tilapia (Oreochromis niloticus) was introduced by UNICEF (Das
et al., 2010). Bangladesh Fisheries Research Institute (BFRI) again
carried a batch of Oreochromis niloticus from Thailand in 1987 and developed
low input and low cost technologies (Das et al.,
2010). For poverty alleviation and livelihood support, tilapia has made
a significant contribution Bangladesh. Tilapia has good resistance to poor water
quality and disease, tolerance of wide range of environmental condition, ability
to convert efficiently the organic and domestic waste into high quality protein,
rapid growth rate and tasty flavour. Tilapia may be cultured as monoculture
and polyculture system. In some cases, monoculture of tilapia is practiced at
the farmers level that might not achieve the total production in polyculture.
Intensive culture system with very high stocking densities and poor water qualities
are encountered with much of the health problems. Due to improper management
disease has become a major problem in fish culture system in Bangladesh (Rahman
and Chowdhury, 1996). Freshwater fishes of Bangladesh may have different
health status, showing disease symptoms like tail and fin rot, gill rot, red
spot, dropsy, EUS, argulosis, nutritional disease and white spot disease (Faruk
et al., 2004). In fish the most obvious external clinical signs are
inflammation, hemorrhage of fins, skin or head, frayed fins, haemorrhaged opaque
eye, necrotic and ulcerative lesions at any location on the body, scale loss
and excessive mucus production (Plumb, 1994). In recent
times, farmers of Mymensingh regions are facing many health problems in the
culture of tilapia.
It was thus necessary to investigate health condition of fish through some suitable techniques. Clinical and histopathological procedures are important tools used to diagnose disease in fish. Clinical investigation provides information on the nature of disease in fish. However, histopathology is an important tool for the diagnosis of disease and it has been successfully used throughout the world. Use of histopathology is limited in Bangladesh due to technical know how and facilities. Thus the present investigation was aimed at observation of the production and health condition of tilapia in Mymensingh region through clinical and histopathological observations.
MATERIALS AND METHODS
Study sites: The experiment was carried out for a period of 7 months
from September, 2010 to March, 2011. Two upazilas of Mymensingh, namely Muktagacha
and Bhaluka (Fig. 1) were selected for the present study because
of tilapia were abundantly cultured species in that area. Four fish farms, two
from Bhaluka Upazila (village Bohuli, 40 km to the southern side of Mymensingh)
and two from Muktagacha Upazila (village Digholgoan, 16 km away from Mymensingh
District) were selected for present study. One pond from each farm having tilapia
was selected randomly. Average depth of pond 1 (P1) was 3.5-4 feet.
Stocking densities of P1 was 220 fry decimal-1. Average
depth of pond 2 (P2) was 4-5 feet and stocking densities was 225
fry decimal-1. On the other hand average depth of P3 and
P4 was 3-4 feet. Stocking densities of P3 was 220 fry
decimal-1 and P4 was 230 fry decimal-1.
Fish sample and environmental data collection: To study health and disease
status of farmed tilapia (Oreochromis niloticus), monthly sampling was
done by seine net and measured to record of weight (g) by the precision balance.
Water quality parameters like temperature, pH, Dissolved Oxygen (DO), alkalinity,
nitrite (NO2) and ammonia (NH3) were determined by using
HACH Freshwater Aquaculture Test Kit (USA). The sampled fish were examined just
after taking out of the container to observe external symptoms and any injury,
infection and other abnormal condition of fish body. For histopathological observation
samples of fish from various organs such as skin, muscle, gill, liver and kidney
were collected by a sharp scalpel and forceps and fixed in 10% formalin. Then
the samples were placed in an automatic tissue processor for dehydration, clearing
and infiltration. The samples were then embedded at a thickness of 5 μm.
|| Location of study sites (Banglapedia)
The sections were then stained with hematoxylin and eosin stains. Then the
sections were mounted with Canada balsam and covered by a cover slip. Then the
slides were examined under a compound microscope (Olympus). Then photomicrographs
from the stained sections taken by using a photomicroscope. Pathological observation
were made from the slides and photographs and compared among different months
of the study period.
RESULTS AND DISCUSSION
All water quality parameters were within suitable range for fish culture except
temperature and alkalinity which were considerably low (18°C and 70 mg L-1)
in the months of December and January. Dissolved oxygen (DO) value did not found
to vary among the ponds and were within the range from 6 to 8.5 mg L-1.
The pH ranged from 6.5-8.5 and ammonia level ranged from 0.001-0.03 mg L-1.
Low temperatures have negative impact on fish health. Hossain
and Paul (1993) observed that the outbreak of EUS was peak when water temperature
was the low, which might be due to the fact that a low temperature fish immune
system ceased to function normally. According to Ahmed and
Hoque (1999), cooler environment with reduced temperature play major role
in the incidence of disease outbreak in the fishes of Bangladesh. Increased
symptoms and pathology in December and January would be due to reduced temperature
and alkalinity during this period. Hossain (2008) mentioned
that, clinical symptoms like scale loss, dermal lesion, loss of caudal fin were
seen in December and January. Ahmed and Hoque (1999)
also reported that clinical signs like gray white necrotic areas were increased
in December, January and February in various carp species in Bangladesh.
Clinically, all the fish of both the upazilas were normal in September, October,
February and March as Fig. 2 shows there are no lesion or
|| Healthy disease free tilapia
However, in November mild lesion, rough skin and scale loss were observed in
some fishes of Bhaluka. It was observed that, more fish affected from December
and January. In December and January, from Bhaluka, fish were observed to have
red spots and deep ulcers in the caudal region (Fig. 3). In
Muktagacha, pale body colour and swollen anus were observed in December shown
in Fig. 4.
Histopathologically it was observed that in skin and muscle of Oreochromis
niloticus, epidermis totally or partly lost, vacuums and necrotic muscle
cells were found from fishes of all ponds (Fig. 5, 6)
during the September, October and November. In December and January, necrotic
muscle with fungal hyphae and fungal granuloma in Bhaluka and trace of fungal
granuloma were found in Muktagacha.
Histopathologically almost normal gill was observed during the months of September
and October. Less affected gills were observed in November. Hypertrophy and
hyperplasia, gill clubbing, haemorrhage in primary gill lamellae and secondary
gill lamellae were lost (Fig. 7, 8) during
December and January in Bhaluka and Muktagacha.
||Tilapia with red spots and caudal lesions in January from
||Tilapia with pale body colour and swollen anus in December
Liver of investigated fish was normal during September, October and March in
both the upazilas. But in November pathologies were found to be started with
few abnormalities. Necrosis, fibrosis, haemorrhage and vacuum was observed in
December and January (Fig. 9, 10). In case
of kidney almost normal structures were observed during the months of September
and October. Presence of fungal hyphae and fungal granuloma in fish of both
upazilas indicated that fishes were suffered with EUS in December and January
(Fig. 11, 12). Ahmed
et al. (2007) found that during December and January, epidermis and
dermis were totally lost and necrotic, whereas, muscles had fungal granuloma
in A. testudineus of investigated farms.
||Muscle of O. niloticus from fish of P1 in
December, epidermis and dermis were lost; necrosis (N), fungal hyphae (Fh),
vacuum (V) and fungal granuloma (fg) were seen. H and E, x125
||Section of muscle from fish of P4 in January, marked
fungal granuloma (fg), necrosis (N) and vacuums (V) were found. H and E,
Hatai et al. (1994) also reported that fungal
hyphae and fungal granulomas in the internal organs and musculature of Colisa
lalia suffering from an invasive mycosis in Japan. Thus it could be mentioned
that tilapia during the period were infected with EUS. Moniruzzaman
(2000) also found almost similar results in skin and muscle of major carps
in winter season. In February, vacuums, melanocytes and protozoan cysts were
found in Bhaluka.
Liver of investigated fishes were highly necrotic and pyknotic having vacuums,
fat droplets, bacterial colony and hemorrhage from the both upazilas during
December and January. Ahmed et al. (2009) also
found similar result Fig. 9. Liver pathology from fishes of
Bhaluka in December. Necrosis (N), fibrosis (fb), Haemorrhage (H) and vacuum
(V) found. for freshwater eel. Liver had highly necrotic hepatocytes, pyknotic
and inflammatory cell during the months of December and January (Roy
et al., 2006).
||Section of gill of from fish of Bhaluka in December, hypertrophy
(ht) and hyperplasia (hy), gill clubbing (gb), hemorrhage (H) in primary
gill lamellae and secondary gill lamellae were lost ().
H and E, x235
||Section of gill obtained from fish of Muktagacha in January,
gill clubbing (gb) and pyknosis (p) in primary gill lamellae were found.
H and E, x125
||Liver pathology from fishes of Bhaluka in December, necrosis
(N), fibrosis (fb), haemorrhage (H) and vacuum (V) found
||Liver pathology from fishes of Muktagacha in December, necrosis
(N) and pyknosis (P) were found
Hossain et al. (2009) reported that severe necrosis
of hepatocytes, pyknosis, vacuoles, fat droplets and hemorrhage were observed
in small indigenous species during December and January. In the present study
it was observed that liver pathology was recovered during February and March.
In the study vacuums, necrosis and pyknosis were found in the month of November.
Ahmed et al. (2009) also observed necrosis, vacuums,
hemorrhage and blood cells in kidney tubule of Unibus testudineus during the
month of November. However, in December and January, degenerated kidney tubules,
many pyknotic nuclei, hemorrhage and inflammatory cells were found. However,
in March, kidney pathology was recovered to almost normal structure except some
From clinical, parasitological and histopathological point of view, fish were
less affected during the months of September, October, February and March and
increased signs and pathology were recorded during the months of colder season
i.e., in December and January.
||Kidney in December from fish of Bhaluka, marked necrosis (N),
wide vacuum (V) and pyknosis (P) were present. H and E, x235
||Kidney from fish of Muktagacha, numerous pyknosis (P), necrosis
(N) and vacuum (V) were found. H and E, x125
This could be due to reduced temperature, alkalinity and dissolved oxygen fishs
metabolic process also reduces and as a result fishes are subjected to be stressed,
infected and diseased. Ahmed et al. (2004) who
examined through clinical, parasitological and histopathological observation
of three small indigenous fishes and found that all fishes were severely affected
in the months of December and January. Ahmed and Hoque (1999)
also mentioned that in freshwater fish, EUS outbreak was most severe during
colder months of the year when water temperature, alkalinity and hardness were
reduced at their minimum levels. Parveen et al. (2005)
found that during winter season water temperature reduced to nearly 10°C
which diminishes antibody in fish. Thus sudden drop of water temperature in
winter season was supposed to be an important predisposing cause of diseases.
Water exchange, reduced feeding, removal of the dead and moribund fishes as
soon as possible are some precautionary measures through which farmers would
be benefited in respect of the control of the diseases (Boungou
et al., 2008; Mohammed and Sambo, 2008; Ibrahim,
From the present study, it was observed that most of the fish of Bhaluka were more affected and less affected fish were found in Muktagacha. P1 in Bhaluka was modified agricultural land and in dry season its water depth remains very low. There are also possibility of being stressed by different pesticides and insecticides deriving from the agricultural lands. Moreover, reduced water depth, temperature and alkalinity might be reasons for increased infection and pathology of fishes during December and January. Under histopathological observation it was found that a great percentage of fish were affected by various pathogens especially bacteria, protozoan parasites, fungal hyphae and fungal granuloma. Thus it is necessary to take more precautionary measures to prevent and control of such diseases. Some preventive measures should be taken before outbreak of such disease. Farmers should apply 500 g lime and 500 g salt per decimal water body especially before winter, when disease outbreak occurs. It might be continued for 3-4 weeks at 7 days intervals. It is expected farmers would be benefited through increased fish production by controlling serious problems in aquaculture like diseases. Government and NGOs should take initiative to give the local farmers hands-on training on fish health management which can increase local and national production rate, ultimately gain economic benefit.
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