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IMPACT OF WATER QUALITY PARAMETERS ON MONOSEX TILAPIA (Oreochromis niloticus) PRODUCTION UNDER POND CONDITION

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The study was conducted at Reliance Aqua Farm in Rahmatpur, sadar upazila, Mymensingh during July to November 2012 to monosex tilapia (Oreochromis niloticus) hatchery ponds with the view to evaluate it's water quality parameters (physico-chemical) for successful production. The samples were collected from Reliance Aqua Farm at Rahmatpur in sadar upazila under Mymensingh district of Bangladesh. The experiment was consisted of three treatments having with two replicates. Six ponds were used for the experiment. The area of each pond was 18 decimal and water depth 1.2 m. Each pond was stocked with tilapia at the density of 200 fish per decimal. There were three treatments which are treatment 1 (T 1) , treatment 2 (T 2) and treatment 3 (T 3) respectively. Artificial feed was applied at 20% body weight at 1 st month (up to 30 days) and reduced to 15% at 2 nd month, 10% at 3 rd month and 5% at the last month of the experiment. Water quality parameters such as water temperature, transparency, pH, dissolved oxygen, ammonia, nitrate and nitrite were measured at ten days interval. Parameters were measured by using thermometer, secchi disc, a portable multiparameter (HACH sension TM 156) meter and HACH device (DR-4000), a direct reading spectrophotometer. It was found that most of the water quality parameters were within suitable range among three treatments. There were no significant differences in temperature among three treatments. But in T 2, all the parameters were within desirable level. However, the highest DO was 7.29 mg/l found in T 2. The ammonia content was 0.36 to 1.325 mg/l in T 3 which was higher than T 1 and T 2. The higher ammonia content in T 3 might be due to the decomposition of uneaten feed. The nitrate concentration was observed with null value (0.0 mg/l) in all the cases. From the present study, it could be said that excess feed (uneaten) which produce ammonia was the main problem for tilapia farming. The problem should be addressed from the view point of research and for better production. Finally, it was observed that among three treatments the highest production was recorded in T 2 (40.19±513.53 kg/dec) compared to T 1 (33.69±26.08 kg/dec) and T 3 (36.14±189.56 kg/dec). The study revealed that the application of artificial feeding influenced the water quality parameters and production of fish in tilapia ponds.
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Int. j. anim. fish. sci. (Online). 2(1):14-21, August 2014, website: www.gurpukur.com or www.gscience.net
IMPACT OF WATER QUALITY PARAMETERS ON MONOSEX TILAPIA
(Oreochromis niloticus) PRODUCTION UNDER POND CONDITION
A. BEGUM1, S. MONDAL2*, Z. FERDOUS3, M. A. ZAFAR4 and M. M. ALI 5
ABSTRACT
The study was conducted at Reliance Aqua Farm in Rahmatpur, sadar upazila, Mymensingh during
July to November 2012 to monosex tilapia (Oreochromis niloticus) hatchery ponds with the view to
evaluate it’s water quality parameters (physico-chemical) for successful production. The samples were
collected from Reliance Aqua Farm at Rahmatpur in sadar upazila under Mymensingh district of
Bangladesh. The experiment was consisted of three treatments having with two replicates. Six ponds were
used for the experiment. The area of each pond was 18 decimal and water depth 1.2 m. Each pond was
stocked with tilapia at the density of 200 fish per decimal. There were three treatments which are treatment
1 (T1), treatment 2 (T2) and treatment 3 (T3) respectively. Artificial feed was applied at 20% body weight at
1st month (up to 30 days) and reduced to 15% at 2nd month, 10% at 3rd month and 5% at the last month of
the experiment. Water quality parameters such as water temperature, transparency, pH, dissolved oxygen,
ammonia, nitrate and nitrite were measured at ten days interval. Parameters were measured by using
thermometer, secchi disc, a portable multiparameter (HACH sensionTM 156) meter and HACH device (DR-
4000), a direct reading spectrophotometer. It was found that most of the water quality parameters were
within suitable range among three treatments. There were no significant differences in temperature among
three treatments. But in T2, all the parameters were within desirable level. However, the highest DO was
7.29 mg/l found in T2. The ammonia content was 0.36 to 1.325 mg/l in T3 which was higher than T1 and T2.
The higher ammonia content in T3 might be due to the decomposition of uneaten feed. The nitrate
concentration was observed with null value (0.0 mg/l) in all the cases. From the present study, it could be
said that excess feed (uneaten) which produce ammonia was the main problem for tilapia farming. The
problem should be addressed from the view point of research and for better production. Finally, it was
observed that among three treatments the highest production was recorded in T2 (40.19±513.53 kg/dec)
compared to T1 (33.69±26.08 kg/dec) and T3 (36.14±189.56 kg/dec). The study revealed that the application
of artificial feeding influenced the water quality parameters and production of fish in tilapia ponds.
Keywords: Monosex, Water quality, Production and Pond.
INTRODUCTION
Fish provides 63% of the animal protein intake in Bangladesh and the annual per capita fish
consumption is 14kg. About 1.4 million people directly and 11 million people indirectly engaged with
fisheries activities (BBS, 1999). Aquatic products are the country’s 2nd largest export commodity
contributing 10% of annual export earning, 5.2% of national GDP and 20% of the agriculture (DoF,
2005). According to a nutrition survey, approximately 30,000 children are becoming blind each year
due to vitamin deficiency (Thilsted et al., 1997). Therefore, any effort to increase animal protein
production must be concentrated on aquaculture. Since augmentation of fish production from rivers and
estuaries is quite difficult, it should depend on pond aquaculture for increasing supply of fish.
Freshwater aquaculture consists mainly of polyculture of carps and monoculture of tilapia and various
catfish in ponds. 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). Tilapia is more easily grown than other foul fish species for either
commercial or non-profit enterprises. In recent years, tilapia culture has become very popular among
the fish farmers. It is currently ranked second only to carps in global production. The predominant
advantage of monosex culture can be achieved in aquaculture situations where one sex displays marked
1Aunguri Begum, Upazilla Fisheries Officer, Department of Fisheries, Dhaka, 2Subrata Mondal, Assistant Professor, Department
of Fisheries & Marine Bioscience, Jessore University of Science & Technology, 3Zannatul Ferdous, Lecturer, Department of
Aquaculture, Bangladesh Agricultural University, Mymensingh, 4Md. Abu Zafar, Lecture, Department of Aquaculture, Hajee
Mohammad Danesh Science & Technology University, Dinajpur and 5Md. Mohsin Ali, Professor, Department of Aquaculture,
Bangladesh Agricultural University, Mymensingh, Bangladesh. *Corresponding author’s Email: subratajstu1975@gmail.com.
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growth superiority, as in male tilapia. Thus, culture of monosex tilapia might prove effective to induce a
positive approach towards tilapia culture in Bangladesh (FAO, 2000). Success of aquaculture depends
almost completely on the quality of different water parameters. Water quality for aquaculturists refers to
the quality of water that enables successful propagation of the desired organisms. These parameters
provide important information about the health of a water body. The quality of the aquatic environment
depends on four kinds of factors, such as physical, chemical, biological and meteorological factors.
Environmental factors are critical in aquaculture, because survival, reproduction and growth of
aquacultural species depend upon a satisfactory environment. The maintenance of good quality of water
is essential for both survival and optimum growth of culture organisms. Good water quality is
characterized by adequate oxygen and limited levels of metabolites. This is because large quantities of
feed is loaded in ponds and excess feed, fecal matter and then metabolites can cause drastic changes in
water quality parameters and sediment chemistry which may affect the growth. As fish is a cold-
blooded animal, its growth, reproduction, maturity and survival mostly depends on water temperature.
Inadequate maintenance of water quality might cause severe problems in tilapia production. Sometimes
lack of maintenance of water quality may cause great loss to the farmers. Therefore, tilapia farming
requires a regular management of water quality for maintaining a suitable environment and to maximize
their production. The main water quality parameters (physico-chemical) are- transparency, temperature,
dissolved oxygen, pH, ammonia etc. The objectives of the study were i) to understand the fluctuation of
water quality parameters in terms of feeding frequency ii) to establish relationship between tilapia
production and water quality parameters.
MATERIALS AND METHODS
The study was conducted at Reliance Aqua Farm in Rahmatpur, sadar Upazilla, Mymensingh during
July to November 2012.
Pond condition: Six rectangular earthen ponds (all ponds were 18 decimal each)
and an average depth of
1.2 m each were used. Ponds were equal in size, depth, basin configuration, bottom types and contour.
The ponds were well exposed to sunlight, not interconnected by inlet and outlet and the main sources of
water were rainfall and water supplied from a pump using a flexible plastic pipe whenever needed. The
embankments were well protected and covered with grass. The water depth was maintained at least 1m.
Experimental design: The experiment was consisted of three different treatments with two replications
each. Treatment 1= applied feed once daily, Treatment 2= applied feed twice daily and Treatment 3= applied
feed thrice daily. Stocking density (200/dec.) of tilapia was same in all treatment.
Pre-stocking management
Pond preparation: All unwanted fishes were eradicated by netting the ponds. Those were manually
cleaned before starting the experiment. The weeds of embankment were also cleaned manually.
Transportation and stocking of fry: Tilapia fry were collected from a fish hatchery “Reliance Aqua
Farm” situated at Trishal, Mymensingh and were transported to “Reliance aqua Farm” at Rahmatpur,
sadar Upazilla, Mymensingh in plastic bags equipped with aerators. Fry were collected from hatchery
stocked in experimental ponds. The initial average length and weight of the fingerlings of tilapia were
7.5 cm and 6 g respectively. Each pond was stocked at the same rate.
Post stocking management
Feeding: Artificial feed was applied at 20% body weight at 1st month (up to 30 days) and reduced to
15% at 2nd month, 10% at 3rd month and 5% at the last month of the experiment. Feed was distributed
evenly over the pond surface. Individual weight of minimum 10% of initially stocked tilapia in numbers
was recorded monthly to estimate the biomass and adjust the feeding rate. The tilapia was sampled by
using a seine net.
Water quality monitoring: Throughout the experimental period the water quality parameters were
determined ten days interval. Water quality measurement and sample were collected in plastic bottles
with stopper having a volume of 250 ml each and marked with hapa number between 08:00 to 10:00
am. Water temperature was recorded with a Celsius thermometer. DO & pH of water samples were
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measured by a Portable Multiparameter (HACH). Alkalinity of water was measured in the Pond
Dynamics Laboratory, Dept. of Fisheries Management of BAU, Mymensingh by the titration method
with the help of 0.02N H2SO4 and methyl orange solution. The concentration of nitrate-nitrogen (NO3-
N) and nitrite-nitrogen (NO2-N) was determined by HACH kit (DR-2010, a direct reading
spectrophotometer) using NitraVer-6 and NitriVer-3 powder pillow. Ammonia-nitrogen (NH3-N) was
also determined by the HACH kit with Rochelle salt and Nessler reagent.
Sampling of fishes: Monthly sampling was done by using a seine net to observe the growth of tilapia to
adjust the feeding rate. Small and rather inadequate sample 5-10 tilapia was taken to make some rough
assessment of growth trends, even knowing that such samples might not present the actual growth
situation. Growth of tilapia in each sampling was measured by using a balance. General pond conditions
were monitored regularly during the culture period. The sampled tilapia was handled very carefully to
prevent handling stress.
Analysis of growth data: The following parameters were used to evaluate the growth of fishes:
Weight gain (g) = Average final weight (g) - average initial weight (g)
Weight gain (%) =
Mean final wei
g
ht Mean initial wei
g
h
t
×100
Mean initial wei
g
h
t
Survival rate
(
%
)
= No. of fish harveste
d
×100
Specific growth rate (%) = (Brown, 1957)
Here, W1= the initial live body weight (g) at time T1 (day) and W2= the final live body weight (g) at
time T2 (day).
Production (kg/dec./120 days): = No of fish caught × Average final weight.
Harvesting of fishes: Fishes were completely harvested on 8 November after 120 days of rearing.
Primarily, the partial harvesting of fishes was performed by repeated netting, using a seine net. Final
harvesting was done by de-watering the ponds by using pump. During harvesting all fishes of each pond
were collected and weighed individually to assess the survival rate and pond production.
Statistical analysis: For the statistical analysis of the data, a one-way ANOVA (Analysis of Variance)
was done by using the SPSS (Statistical Package for Social Science) version-20.00. Significance was
assigned at 1% level of probability.
RESULTS AND DISCUSSION
Results
Water quality parameters
Various types of water quality parameters were observed during the study period. Water and air
temperature (ºC), transparency (cm), dissolved oxygen (mg L-1), pH, ammonia (mg L-1), nitrate (mg L-
1), nitrite (mg L-1) were measured after ten days interval. One way analysis of variance (ANOVA) was
performed to observe whether any difference exists in the mean values of water quality parameters
among different treatments. Water quality parameters of three treatments have been presented in table 2.
Table 2. Mean (±SE) values of water quality parameters recorded from different treatments.
Parameters Treatments Level of significance
T1 T2 T3
Air Temperature (°C) 30.25±0.14 30.25±0.14 30.25±0.14 NS
Water Temperature (°C) 31.27±0.22 31.33±0.22 31.20±0.21 NS
Transparency (cm) 36.63±0.36 34.38±0.36 34.98±0.36 **
Dissolved oxygen (mg L-1) 4.56±0.15 5.78±0.16 4.62±0.15 **
pH 6.84±0.03 7.38±0.08 6.87±0.04 **
Ammonia (mg L-1) 0.31±0.02 0.40±0.03 0.80±0.04 **
Nitrite (mg L-1) 0.02±0.0 0.03±0.0 0.13±0.04 **
Nitrate (mg L-1) 0±0 0±0 0±0 NS
** = Significant at 1% level of probability and NS = Not significant.
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Physical parameters
Air temperature (°C): Air temperature was same for all the experimental ponds on each sampling day.
The air temperature ranged from 29 to 31.5°C during experimental periods. The maximum air
temperature was 31.5°C and the minimum air temperature was 29°C. The mean values of air
temperature were 30.25±0.14°C in all treatments. The statistical analysis showed that there was no
significant difference (P>0.05) among temperature values recorded in different treatments.
Water temperature (°C): The water temperature of experimental ponds was found to vary from 30 to
34.5°C. The mean (±SE) values of water temperature were 31.27±0.22, 31.33±0.22 and 31.20±0.21°C
during the experiment in T1, T2 and T3 respectively. There was no significant difference (P>0.05)
among three treatments, when statistical analysis was performed.
Transparency (Cm): The mean (±SE) values of transparency were 36.63±0.36, 34.38±0.38 and
34.98±0.55 cm in T1, T
2 and T3 respectively. The statistical analysis showed that the values were
significantly different.
Chemical parameters
Dissolved oxygen (mg L-1): The level of dissolved oxygen varied from 3.21 to 7.29 mg L-1 in three
treatments. The mean values of DO were 4.56±0.15, 5.78±0.16 and 4.62±0.15 mg L-1 in T1, T2 and T3,
respectively. The highest value was found 7.29 mg L-1 in case of T2 and the lowest value was recorded
3.21 mg L-1 in T1.
PH (Hydrogen ion concentration): The mean values of pH were 6.84±0.03, 7.38±0.08 and 6.87±0.04 in
T1, T2 and T3 respectively. The statistical analysis showed that the values were significantly different.
Ammonia (mg L-1): The level of ammonia content varied from 0.105 to 1.325 mg L-1 in three treatments
during the experimental period. The ammonia content was 0.105 to 0.52, 0.2 to 0.7, 0.36 to 1.325 mg L-
1 with mean value of 0.31±0.02, 0.40±0.030 and 0.80±0.04 mg L-1 in T1, T2 and T3 respectively. The
highest value was 1.325 mg L-1 in T3 and the lowest value was 0.105 mg L-1 in T1.
Nitrite (mg L-1): During the study period, the value of nitrite varied from 0 to 0.67 mg L-1 in six selected
culture ponds. The mean value of nitrite content was 0.02±0.0, 0.03±0.0 and 0.13±0.04 mg L-1 in T1, T2
and T3, respectively. The maximum (0.67 mg L-1) and minimum (0.003 mg L-1) nitrite levels were
observed in T1 and T2 respectively.
Nitrate (mg L-1): Nitrate content of experimental ponds was found zero (0.0 mg L-1) in all the cases
(Table 2).
Growth and production of tilapia
The growth and production parameters of tilapia in three treatments are shown in table 3. The mean
stocking weight of tilapia was 6.0±0.0 in three treatments. At the end of the experiment the final weight
were 197±1.0, 219.0±1.0 and 212±2.0 in T1, T2 and T3 respectively. So the individual mean weight gain
of tilapia was 191±1.00, 213±1.00 and 206±2.00 in three treatments respectively. The mean specific
growth rates (SGR) of tilapia were 1.26±0.0, 1.30±0.0 and 1.29±0.0 in all the treatments respectively.
Table 3. Mean (±SE) values of growth parameters recorded for tilapia (Oreochromis niloticus).
Growth parameters Treatment Level of
significance
T1 T2 T3
Initial weight (g) 6.0±0.00 6.0±0.00 6.0±0.00 NS
Final weight (g) 197±1.00 219±1.00 212±2.00 ∗∗
Weight gain (g) 191±1.00 213±1.00 206±2.01 ∗∗
% of weight gain 3183.33±16.72 3550±16.72 3433.33±3343 ∗∗
SGR (% per day) 1.26±0.00 1.3±0.00 1.29±0.00 NS
Survival (%) 85.5±0.50 91.75±0.75 85.25±1.25 ∗∗
Production (kg/dec/120 days) 33.69±26.08 40.19±513.53 36.14±189.56 ∗∗
** = Significant at 1% level of probability and NS = Not significant
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The ANOVA results showed that the specific growth rate of tilapia was not significantly different in
different treatments. The mean survival rate of tilapia was 85.5±0.50, 91.75±0.75 and 85.25±1.25 in T1,
T2 and T3 respectively. These values were significantly different. The mean productions were
33.69±26.08, 40.19±513.53 and 36.16±189.57 kg/dec/120 days in three treatments, respectively. The
ANOVA results showed that the production of tilapia was significantly different in different treatments.
The production of tilapia in three treatments is shown in fig. 1.
Fig. 1. Production of tilapia in three treatments.
Discussion
Water quality parameters
The maintenance of good water quality is essential for both survival and optimum growth of culture
organisms. Environmental factors govern growth, survival and feed consumption of tilapia (Fry, 1971
and Brett, 1979) and aquaculture almost depends on the water quality, i.e. qualities of aquatic
environment. Therefore, it is generally believed that the suitable range of water quality parameters
ensure the better management of aquatic organisms as well as aquatic environment. Water temperature
is one of the most important water quality parameters that influence the growth, food intake,
reproduction and other biological activities of aquatic organisms. Generally, the metabolic demand for
oxygen in aquatic animals double or triples with every 10°C increase within the range of temperature
that the animal can tolerate. Aminul (1996) stated that the water temperature ranged from 28 to 35°C is
suitable for fish culture. In the present study, water temperature varied from 30 to 34.5°C with the mean
of 31.27±0.22, 31.33±0.22 and 31.20±0.21°C respectively which might be fluctuated due to seasonal
changes, changes of sun brightness, time and length of the day. The water temperature of experimental
ponds ranged from 30 to 34.5°C during the experiment in different treatments, which was more or less
similar to Asaduzzaman et al. (2005), Rahman (2005), Asaduzzaman et al. (2006) and Kunda et al.
(2008). FAO (1981), DoF (2009) and observed that the optimum temperature for aquatic production
were 23-31°C, 25-30°C and 26.5-31.5°C, respectively which is more or less similar to the findings of
the present study. Water transparency grossly indicates the presence or absence of natural food particles
of fish as well as productivity of a water body. It has an inverse relationship with the abundance of
plankton. Boyd (1990) noted that the transparency of water was affected by many factors such as silt,
microscopic organisms, suspended organic matter, season of the year, latitude and intensity of light,
application of manure, grazing pressure of fishes and rainfall. Transparency between 15 to 40 cm is
appropriate for fish culture. The mean values of transparency were 36.63±0.36, 34.38±0.38 and
34.98±0.55 cm in T1, T2 and T3 respectively, which was more or less similar with the findings of
Kohinoor et al. (2001) as recorded values ranging from 15-58cm. Wahab et al. (1995) suggested that
the transparency of productive water should be 40 cm or less.
The gases, which are found in dissolved condition in natural waters, the most important and critical one
is oxygen. Maintaining good levels of DO in water is essential for successful production since oxygen
(O2) has a direct influence on feed intake, disease resistance and metabolism. A sub-optimal level is
very stressful for fish. Regular supply of dissolved oxygen is required for all kinds of aquatic organisms
except anaerobic bacteria. It is therefore important to continuously maintain dissolved oxygen at
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optimum levels of above 3.5 ppm. In the this study, dissolved oxygen varied from 3.21 to 7.29 mg L-1
with a mean of 4.56±0.15 and 5.78±0.16 mg L-1 in three treatments during culture period. DoF (1996)
reported that the range of dissolved oxygen suitable for fish culture would be 5.0 to 8.0 mg L-1. The
concentration of dissolved oxygen in the present study was similar to findings of Alam et al. (1997), Ali
et al. (2004) and Asaduzzaman (2005) who recorded dissolved oxygen ranged from 4.0 to 7.0, 4.3 to
6.9 and 1.2 to 7.2 mg L-1 respectively which was more or less similar to the present study. Boyd (1998)
found the desired concentration of DO 5-15 mg L-1 which was far from the findings in this study. The
pH is considered as an important factor in fish culture and treated as the productivity index of a water
body. An acidic pH reduces the growth rate, metabolic rate and other physiological activities of fishes
(Swingle, 1967). In the present study, pH ranged from 6.5 to 7.33 during the culture period. The mean
values of pH were 6.84±0.03, 7.38±0.08 and 6.87±0.04 in T1, T2 and T3 respectively. The pH level of
ponds water under different treatments was approximately neutral. The desired concentration of pH was
7-9 (Boyd, 1998). The pH value recorded from the experimental ponds agreed with the findings of
Ahmed (2004), Ali et al. (2004), Fatema (2004), Asaduzzaman (2005) and Asaduzzaman et al. (2006)
who found the ranges of pH from 6.3 to 8.9, 7.55 to 7.84 and 7.51 to 7.91 respectively. Kunda et al.
(2008) Alam et al. (1997) found pH values ranges from 7.0 to 9.0 and 8.0 to 9.5 which were slightly
different with the findings of the present study as well.
Ammonia is a very important parameter for good fish production. Ammonia in water exists in two
forms, as ammonium ions (NH4
+), which are non toxic and as the un-ionized toxic ammonia (NH3). The
desirable range of ammonia for fish farming was <0.1 mg L-1 (Boyd, 1998). The presence of ammonia
in fish pond water is normal due to natural fish metabolism and microbiological decay of organic
matter. As little as 0.6 mg L-1 free ammonia (NH3) can be toxic to many kinds of fish and shrimp,
causing gill irritation and respiratory problems. The higher water temperature and pH, the greater the
concentration of the toxic ammonia form (NH3). The mean values of NH3 were 0.31±0.02, 0.40±
0.03and 0.80±0.04 mg L-1 in T1, T2 and T3 respectively which were more or less similar to Rahman
(2005) and Asaduzzaman et al. (2006) who recorded ammonia value ranged from 0.01 to 0.82 and
0.203 to 0.569 mg L-1 respectively. The findings of the present study were more or less similar to the
findings of Boyd (1998), DoF (2009) and FAO (1981). Nitrite is another form of nitrogenous compound
and an intermediate product of the transformation of ammonia into nitrate by bacterial activity. More
recent evidence indicates that nitrite may be a significant limiting factor in fish production ponds. The
absorbed nitrites from the gut bind to haemoglobin and reduce its ability to carry oxygen. Nitrite can be
associated with ammonia concentration in the water body. At 2 ppm (mg L-1) and above, nitrites are
toxic (injurious or lethal) to many fish and shrimp. The recommended level of nitrite for fish farming
was <0.3 mg L-1 (Boyd, 1998). Alim (2005) recorded nitrite concentration ranging from 0.00 to 1.021
mg L-1 that was more or less similar to the findings of present study. Nitrates are the final products of
the aerobic decomposition of organic nitrogen compounds, which are generated from nitrites by
oxidation and reduce to ammonia by bacterial action. Nitrate-nitrogen is usually occurs in relatively
small concentration in unpolluted freshwater. Nitrate is added to the ecosystem as a byproduct of
nitrification. It is removed from the solution through the utilization of green plants and through bacterial
denitrification to uncombined nitrogen and reduction to ammonia-nitrogen. They are present in low
concentration in all surface water. In the present study nitrate content of water is null (0.0 mg L-1). It
might be due to the no use of nitrogenous fertilizer, which is the main source of nitrate pollution in
surface water and the discharge of sewage effluent from treatment ponds.
Effect of feed on water quality parameters
It is well established that the success of fish culture depends largely on feeding. Both floating and
sinking feed can produce satisfactory growth. Determining whether feeding rates are too low or too
high is important in maximizing fish growth and feed use efficiency. Feeding rates and frequencies are
in a part of a function of fish size. But overfeeding is a waste of expensive feed. It also results in water
pollution, low dissolved oxygen levels, increased biological oxygen demand and increased bacterial
loads. Feed also affects the productivity of a water body. In the present study, T2 was applied feed twice
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daily which showed the best growth performance and survivability. This indicated that fish should feed
at optimal level so that the water quality parameters were suitable for fish growth. The water quality
parameters measured in all ponds were founds within acceptable range for fish culture and there was no
significant difference among the treatments.
Growth and production performance of tilapia
The production of tilapia in different treatments found to vary among treatments due to difference in
survival and growth rate. A significant difference was observed in production among three treatments.
The production was calculated on per decimal basis over 120 days culture period. The mean survival
rate of tilapia was 85.5±0.50, 91.75±0.75 and 85.25±1.25 in three T1, T2 and T3 respectively. The mean
productions were 33.69±26.08, 40.19±513.53 and 36.16±189.57kg/dec./120 days in three treatments,
respectively. Significantly the highest production of tilapia was obtained in T2 and the lowest in T1.
Fatema (2004) and Rahman (2005) obtained tilapia production with freshwater prawn in periphyton-
based culture from 27.11 to 35.23, 21.55 to 34.45 and 35.62 to 43.09 kg/dec. respectively which were
slightly respectively, lower than the present study. The mean weight gain of tilapia was 191±1.00,
213±1.00 and 206±2.01 in three treatments respectively. The production of tilapia was high in T2 where
feed applied twice daily which supported better production performance of fishes than T1 and T3. In T3
feed applied thrice daily which was cost effective. Besides, excess feed produce ammonia which is
health hazardous. So, from this experiment it might be concluded that culture of tilapia by supplying
feed twice daily enhance production of fishes and earns profit.
CONCLUSION
It may be concluded that water quality parameters vary with feeding frequency and have wider impacts
on primary productivity and fish production. So excessive feeding was discouraged and feeding twice in
a day is essential for better production. Finally, there are some general recommendations for farmers to
maintain the optimum level of water quality parameters in tilapia farms which may be helpful to obtain
the better production of fish and ensuring the environmental sustainability. The recommendations are
excessive feeding should be avoided water exchange should be done if required and regular monitoring
of the ponds should be done.
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