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Figure 1. Growth performance of Oreochromis shiranus cultured in earthen ponds fertilized using broadcasting, bagging and crib methods. |
| Livestock Research for Rural Development 24 (4) 2012 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This experiment was carried out in earthen ponds of 200 m2 at Bunda College of agriculture students’ farm to compare the effectiveness of broadcasting, bagging and crib as methods of pond fertilization of organic manure on growth and survival of Oreochromis shiranus for 90 days.
There were significant differences (P<0.05) in growth of fish between treatments with crib method showing higher growth of fish and had final mean weight of 23.9±1.32g followed by bagging method which had the final mean weight of 20.9±2.31g and finally broadcasting method with final mean weight of 19.91±3.09 g. There were no significant differences (P>0.05) between the treatments in amount of chlorophyll a when broadcasting, bagging and crib method were used and also survival rate did not show any significant differences (P>0.05). The results of the experiment would help the small-scale fish farmers to use cribs in their ponds as a way of fertilizing the ponds to attain higher yields.
Key words: Pond fertilization, Tilapia rendalli, semiintensive system, chlorophyll a, organic manure
Pond fertilization involves the application of both organic and inorganic fertilizers in order to increase the production of the natural food organisms which are then eaten by the fish. These natural food organisms include the phytoplanktons, zooplanktons, periphytons and insects (Brummet 2000). These are all part of a complex food web converging towards the fish production. By increasing the availability of major nutrients, fertilizers promote the development of the planktonic algae, which provide food for many fishes. Fertilization also leads to the development of animals which feed on algae including tilapia which are herbivorous (Boyd 1982).
When organic or inorganic fertilizer is added to the fish pond, the nutrients dissolve in water where the greatest portion is taken up by the phytoplankton present either to be stored or assimilated and used for growth and reproduction (FAO 1997). Organic manure from plants and animals is used to fertilize the pond and, as this is applied in the pond, fish might use it as a feed (Chakroff 1978). Out of all organic manures, chicken manure is the best because urine is added to the fecal material in the cloaca during digestion which increases its nitrogen percentage (FAO 1997).
Fish yield depends on natural productivity which depends on the nutrient availability in pond soils and water. Fertilization can also increase nutrient content in the pond (Arrignon 1998). Nitrogen, phosphorous and potassium are the most important nutrients that enhance natural production. These nutrients are supplied by organic and inorganic fertilizers. Fertilizers are applied in the pond to stimulate and maintain plant growth and establish secondary food chain. Fertilizers applied in the pond alter the physical, chemical and biological status of the water and this determine the survival, growth and production of fish in the pond (Arrignon 1998).
In pond fertilization with organic manure, there are different methods involved of which some are more advantageous than the others. Some of these methods include broadcasting, use of compost crib and bagging (Hecht 2006). When using these methods, the main aim is to establish and maintain a dense growth of planktons which color the water with a rich shade of green and this is called planktonic bloom (Boyd 1982).
Fish as a source of rich food for poor people plays an important role in improving Africa’s food security and nutritional status (NAGA 2005). As such, the government of Malawi is promoting aquaculture to supplement the dwindling catches from capture fisheries (Makwinja 2005). However, there are several limitations in aquaculture production which include expensive formulated feed, lack of aquaculture extension expertise, lack of reliable water sources, just to mention a few. The possible alternative in Malawi as a developing country is pond fertilization.
Despite that formulated feeds are expensive, small scale fish farmers are also facing the problem of poor growth and survival of fish. This problem is caused when some water quality parameters like temperature, pH, alkalinity, concentration of phosphorous, calcium, and ammonia are altered. When organic manure is applied in the fish ponds, the water quality is altered and also the method used would also determine the rate of change of the water quality. Therefore, lack of knowledge on effectiveness and cheap method of manure application are contributing factors to this problem. The fish production does not only rely on availability of feeds in the ponds but also on water quality. Water quality parameters play a significant role in biology and physiology of fish (Boyd 1998; Mertinez-Palociosset et al 2002). Through out the period of this experiment, the water quality parameters remained within the favorable range required for Oreochromis shiranus which are as stated in Table 1.
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Table 1. The recommended water parameter levels for Oreochromis species. |
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Water quality parameter |
Recommended Level |
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Temperature |
200C-350C |
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pH |
5-11 |
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An un ionized ammonia |
2.4 mg/l |
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Dissolved oxygen |
>1 mg/l |
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Salinity |
13.5% |
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Source of data: Lovell 1998; Fryer and Iles 1972. |
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To minimize these problems of rising prices of formulated feeds, poor growth and low survival of fish in most small scale fish farms in Malawi, there is need to find the best method of manure application that will result in high production of primary products thereby improving growth and survival of fish in ponds and hence improving the living standards of local fish farmers. Natural feeds will lead to high production of fish in ponds because they provide food for fish. This leads to improved living standards of the farmers since the farmers use the fish for food and sell the surplus. This experiment was therefore conducted to identify the best method of organic manure application that should be used to achieve maximum production in small scale ponds, specifically to compare the effectiveness of broadcasting, compost crib and bagging methods of fertilizing the pond with organic manure.
The experiment was carried out at Bunda College fish farm using 9 earthen ponds of 200 m2 for 3 months during the months of November 2009 to January 2010. The water source was the Bunda Reservoir.
The ponds were drained and allowed to dry. Then the mud was removed. Lime was applied in all the ponds using the application rate of 2000kgs/ha (20kgs/200m2). Fish were stocked on 26th October, 2009 at the rate of 2 fish per m2 which was chosen basing on the fact that the system that was practiced was falling under semi-intensive system which recommends the stocking rate of 2-4 fish per m2. Each pond was stocked with 400 fish. Fish of average weight of 7.2g were stocked because O. shiranus start spawning as early as 12g so to avoid stocking bloodstocks that is why 5-10g fish were chosen. Before stocking, the fish weight and the total length measurements were taken.
This activity started 2 weeks before stocking the fish because there was no supplemental feed that was given to the fish as such prior application helped the fish to find the primary products already existing in the pond. The application rate was 250 kg/ha per week.
Fish sampling was done every month throughout the experimental period. It was done at an interval of 1 month. The sample size was 10% of the stocked fish in each pond. After each sampling, the data that was collected included fish body weight in grams (using an electronic scale) and its total length in millimeters (using a ruler). Data of mortalities was also collected and recorded.
The initial data on water quality parameters was collected. Thereafter, water quality parameters like salinity, pH, turbidity and dissolved oxygen were measured at 0800hrs and 1400hrs every day. Chlorophyll a was also monitored and data collected every month using spectrophotometry method. These water quality parameters were determined using a Horiba (NTU) water checker from Tokyo in Japan.
The experiment was laid out in a completely randomised design (CRD). The treatments which included broadcasting, bagging, crib methods of pond fertilization, were assigned to nine ponds used at random.
The formulae used in measuring growth, weight gain, percent increase in weight and survival rate were as follows:
SGR= [(lnWt1 - lnWt0)/t2-t1] *100
Where: Wt1 =final weight of fish
Wt0 = initial weight of fish at stocking time
t = time
ln = natural log
SR= [(# of fish stocked- # of fish died)/ # of fish stocked]*100
Wt gain = final wt- initial wt
% increase in wt = {(final wt- initial wt)/initial wt}*100
Data on growth, survival, and primary production was analyzed using one way Analysis of Variance (ANOVA) and where significant differences appear, treatment means will be separated using Duncan’s Multiple Range Test (DMRT). The Mathematical Model of the experiment was γij = μ + ti +εij Where: γij = jth observation on ith treatment; μ = overall treatment mean; ti = effect of the ith treatment; and εij = error component associated with jth unit on the ith treatment.
The final weight was compared and found to be significantly different (P<0.05) between the treatments. The highest final weight was noted in the treatment where crib method was used (23.9g) while broadcasting and bagging methods had the final weights of 19.9g and 20.9g, respectively. Likewise, when the weight gains were compared between the treatments, the results showed significant differences (P<0.05) (Table 2, Figure 1).
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Figure 1. Growth performance of Oreochromis shiranus cultured in earthen ponds fertilized using broadcasting, bagging and crib methods. |
There were no adverse mortalities observed hence the survival rate was found to be insignificant between the treatments (P>0.05). Though there are no differences between the treatments, ponds fertilized using bagging method had the highest survival rate of 86.1% and followed by those ponds fertilized using broadcasting method (85%) and lastly crib method which had the survival rate of 73.9% (Table 2).
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Table 2. Effects of the treatment on growth performance of Oreochromis shiranus cultured in earthen ponds (Means ± SE). |
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Parameter |
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Treatment |
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Broadcasting |
Bagging |
Crib |
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Initial wt (g) |
6.31±0.1 |
7.12±0.1 |
7.07±0.1 |
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Final wt (g) |
19.9±3.1a |
20.9±2.3a |
23.9±1.3b |
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Wt gain (g) |
13.8±2.9a |
13.3±2.9a |
16.1±0.7b |
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SGR (%) |
1.24±0.3 |
1.23±0.6 |
1.41±0.5 |
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Increase in wt (%) |
246±42a |
194±50b |
231±22a |
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Survival (%) |
85.0±3.3 |
87.3±10.3 |
73.9±6.2 |
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abThe means with different supercripts are significantly different (P<0.05) |
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At the end of the experiment, it was noticed that temperature and pH were not significantly different (P>0.05) but dissolved oxygen showed significant differences (P<0.05) between the treatments. Chlorophyll a was highest in ponds fertilized with chicken manure using crib method (80.22 µg/l) followed by ponds which were broadcasted (79.29 µg/l) then ponds which were fertilized using bagging method (78.28 µg/l) but these were not significantly different. It was observed that the overall mean temperature was 25.9 °C and dissolved oxygen was 2.8mg/l. mean pH was found to be slightly above 8 (8.5) (Table 3).
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Table 3: Summary of water quality parameters in earthen ponds of Oreochromis shiranus. |
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Parameter |
Treatments |
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Broadcasting |
Bagging |
Crib |
| pH | |||
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AM PM |
8.32±0.06 8.68±0.08 |
8.39±0.28 8.86±0.16 |
8.33±0.11 8.57±0.05 |
| Oxygen (mg/l) | |||
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AM PM |
2.72±0.08a 2.94±0.01 |
2.59±0.08b 2.91±0.01 |
2.56±0.01b 2.94±0.01 |
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Mean turbidity (NTU) |
165.8±3.4b |
160±2.8b |
201±3.7a |
| Temperature (°C) | |||
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AM PM |
24.3±0.03 27.6±0.09 |
24.3±0.03 27.6±0.09 |
24.2±0.10 27.4±0.19 |
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Salinity |
0.01±0.01 |
0.01±0.01 |
0.01±0.01 |
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Chlorophyll a (µg/l) |
79.3±0.64 |
78.3±0.51 |
80.2±1.15 |
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abThe means with different superscripts are significantly different (P<0.05) |
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The final mean weight gain was highest (16.11g) in the treatment which crib method of pond fertilization was used. Broadcasting method indicated 13.78g and bagging method indicated 13.28g weight gains. The fish’s growth increased at an increasing rate in all the three treatments in the first 30days but later growth at a decreasing rate was observed in ponds treated with bagging and crib methods of pond fertilization. Again the specific growth rate was observed to be higher at the beginning and later dropped. This means that the growth of Oreochromis shiranus, in this case varied with time. High growth of fish in ponds fertilized using crib method is attributed with high primary production that was observed in the ponds and algae have high protein, fat and ash content which could have influenced the high growth of the fish and zooplanktons (De Silva 1993).
The high growth was also observed in crib method due to the fact that fish were going into the crib to graze where they find worms and other rubbish which they eat and feed on the manure especially on uneaten staff (Lulenga 1997). In addition to that, Balarin (1979) reported that productivity of fry and planktivorous adults will therefore be determined by the productivity of the pond and pond fertilization is often implemented as a means of increasing fish production. He further said that productivity of a pond will depend both on the quantity of natural and supplementary feeding, and there is direct relationship between primary production and growth of fish. This means that the high growth of Oreochromis shiranus in ponds treated with crib method was due to high productivity of primary products.
According to Blakely and Hrusa (1989), bagging method is one of the best method of pond fertilization since it makes sure that the nutrients remain in the water column and off the bottom for as long as possible to insure complete nutrient dispersal. To complement what Blakely and Hrusa (1989) reported, this method came second in terms of growth performance from crib method because the fish only relied on the released nutrients from the porous bag. There was poor performance of growth in the ponds fertilized using broadcasting method because Blakely (1989) in addition reported that this method causes a significant loss of the manure to the bottom making them unavailable to the pond. Boyd and Hrusa (1982) also reported that despite that broadcasting method provides even distribution of manure, it has the disadvantage that as the manure is broadcasted over the pond, and much of the mineral content is wasted as it is tied up in the bottom sediments hence can lead to poor primary production. Furthermore, as manure is spread over the entire pond surface can lead to deoxygenation and it is preferable to put manure in heaps in a crib around the water’s edge to restrict the anoxic zones.
Throughout the experiment, the water quality parameters in all the treatments remained within the favorable range required for growth and survival of tilapia. The water condition was beneficial to the fish as the water quality play a significant role in the biology and physiology of fish (Boyd 1998; Mertinez-Paliosset et al 2002). The primary production was determined using the analysis of chlorophyll a and this showed no significant differences (P>0.05) when the treatments were compared. Despite no significant differences in terms of primary production between the treatments, ponds fertilized using crib method showed higher means of chlorophyll a levels than broadcasting and bagging method.
Manure was applied two weeks before the fish were stocked. This was done to make sure that the fish should find already made primary products since there was no supplemental feed that was given to the fish. It was observed that there were insignificant differences in terms of primary production when the different methods of manure application were used. However, rib method showed higher production of primary products than other methods. This is due to the fact that cribs provide good distribution of manure if well constructed and managed (Lulenga 1997).
The primary product that was measured in this research was chlorophyll a and this is the green pigment found in plants that allows them to convert sunlight to energy. Chlorophyll a measurement indicates the biomass of phytoplankton in a culture unit and it is well established that phytoplankton productivity is positively correlated with nutrient concentrations (Boyd 1990).
Ponds fertilized using bagging, broadcasting and crib methods showed no significant differences in survival rate. This indicates that the water level was within good levels above wooden stakes to prevent predation (Lulenga 1997). During the experiment it was noticed that the temperature, dissolved oxygen, turbidity and salinity were within acceptable ranges for tilapia (Balarin 1979; Boyd 1990).
According to Delince (1992), pH below 4 and above 11 are lethal to most fish including Oreochromis shiranus and the pH values ranging from 6.5 to 9 are considered as optimum. Blakely (1989) also reported that pH above or below the optimum levels will lead to poor growth and reproduction. It was also observed that the dissolved oxygen range throughout the experiment was ranging from1.86 to 7.09mg/l but according to Blakely and Hrusa (1989), the tilapia, carp and Clarias species tolerate a lower lethal limit of between 1.0 mg/l and 2.0 mg/l of dissolved oxygen.
Furthermore, these species are able to withstand moderate to prolonged exposure to waters of approximately 3.0 mg/l dissolved oxygen without major adverse effects to their health and feeding behavior (Blakely and Hrusa 1989). From the data on water quality it can be concluded that all the treatments provided the optimal level for growth and survival of Oreochromis shiranus. This suggests that the method and the rate of manure application used do not have adverse effects on water quality but instead provide the optimal levels.
The ponds which were fertilized using crib method showed higher fish growth rates than ponds fertilized using broadcasting and bagging methods. The primary production levels were in acceptable levels to make enough feed for the fish. The survival rates were not affected by treatment. Based on the growth, crib method may be encouraged as one way of fertilizer application options.
The authors sincerely appreciate and offer a profound gratitude to the Department of Aquaculture and \Fisheries Science for the facilities used during the experiment. We also thank Mr. E. Nyali for the assistance during the laboratory work and Mr. L.S. Sibili for the support and collaboration on various issues that needed immediate attention during the period of research project.
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Received 24 February 2012; Accepted 12 March 2012; Published 2 April 2012
