Comparison of natural pond system with an intensive (indoor) system for raising Cachama (Colossoma macropomu) and Tilapia (Oreochromis niloticus)

Tick Nouanthavong and T R Preston*

Living Aquatic Resource Research Center (LARReC), Lao PDR
tick_a@hotmail.com
* TOSOLY, AA #48, Socorro, Santander, Colombia

Abstract

Two systems of fish culture: intensive in indoor tanks and natural in outdoor ponds; and  two species of fish: Tilapia (Oreochromis niloticus) and Cachama (Colossoma macropomu) were compared in a 2*2 factorial arrangement with 3 replications.  The fish in the intensive system were raised in plastic tanks of 0.5 m3 capacity (50 fish per tank) and given commercial fish feed (35% crude protein) at 3-5% of live weight. The ponds in the natural system (2*2*1.5m) were lined with polyethylene film and fertilized with biodigester effluent (240 mg N/m²/day); supplementation was with fresh duckweed (Lemna minor) and Taro leaves (Colocacia esculenta).  

Over a 60 day period, both Tilapia and Cachama grew faster in weight and length, and in weight/length ratio, in the intensive system than in the natural system. In both systems the Tilapia grew faster than the Cachama. Less supplement DM was required per unit live weight gain for the Tilapia in the natural than in the intensive system, with the implication that despite the slower growth rates, the economic analysis would favour the former.

Key words: biodigester effluent, duckweed, fish feed, phytoplankton, supplementation, Taro

Introduction

There is a need to study alternative systems of fish production that do not depend on purchased feeds and which make better use of available resources in farming systems that recycle organic wastes. The objectives are to reduce the present dependency on imported concentrate feeds and to encourage farmers to adopt farming methods that are more economically viable. In an integrated farming system nothing is wasted, the byproduct of one system becomes the input for another. By contrast, in the intensive system, the fish are given supplementary feeds the residues from which can be a source of pollution.

In the natural pond system the strategy is to fertilize the water to encourage the growth of phytoplankton which become the main source of feed. Supplements may also be given but usually these are in the form of water plants such as duckweed and water spinach, which can be grown locally. By contrast, in the intensive system the feed is provided in a concentrated form with a high protein content made from ingredients that are purchased from outside the farm.

The importance of the natural system has been realized of late and the scientific basis is being investigated to evolve appropriate technologies to get optimum productivity of the land, labour, waste and water. Better integration of the systems to involve crop and livestock production with recycling of wastes for aquaculture can help small-holder farmers to diversify their farm production, increase cash income, improve quality and quantity of food produced and exploitation of unutilized resources particularly labour and waste. More emphasis is needed on the integration of fish farming with agriculture and irrigation, livestock farming, sewage utilization and water pollution control not only to increase the productivity of land and water and improve the economic conditions of poor farmers but also to maintain health and hygiene of the rural poor and city dwellers alike.

The two main components of the natural system are: (i) the means to fertilize the growth of phytoplankton; and (ii) the choice of water plants that can be a direct feed source to the fish. Early research used animal manures as replacement for chemical fertilizers (Cruz and Shehadeh 1980). Later research evaluated the processing of the manure in biodigesters and the use of the biodigester effluents as fertilizer in the pond (Edwards et al 1988; Pich Sophin and Preston 2001; San Thy and Preston 2003). Biodigester technology has developed considerably in the last decade and the use of low-cost tubular polyethylene has enabled the process to be within the reach of poor farmers (Bui Xuan An et al 1997; Doung Nguyen Khang and Le Minh Tuan 2002).  The recycling of waste gives additional value to both human and animal wastes through gas production, production of good quality fertilizer and the control of pathogens.

Duckweed has been used successfully as feed for mixed fish species in outdoor ponds fertilized with biodigester effluent (San Thy et al 2008; Sen Sorphea et al 2010). The leaves of Taro (Colocacia esculenta) have been shown to have high nutritive value for pigs (Chhay Ty et al 2010; Du Thanh Hang and Preston 2010; Manivanh Nouphone and Preston 2011) and ducks (Giang et al 2010). Recent observations indicate that the fresh whole leaves of Taro are readily consumed by Cachama (Colossoma macropomum) and Tilapia (Rodriguez Lylian, personal communication).  Duckweed and Taro grow naturally in most villages in SE Asia.

Hypothesis

A natural pond system for raising Cachama and Tilapia fish will be more economical than raising them indoors in plastic tanks with purchased fish feed.     

Materials and methods

Location and climate

The experiment was conducted from 15 August to 15 November 2010 at An Giang University, An Giang Province, Long Xeing district of Vietnam. In An Giang Province in the Mekong Delta, the rainy season is from June to November. Average temperature is around 25^oC, with a maximum of about 40^oC in April, while the coldest month is January, when the temperature is around 22^oC, with a maximum of about 35^oC. 

Experimental design

Four  treatments were compared in a 2*2 factorial arrangement with 3 replications.

System:

• IS: Intensive system using fish feed concentrate in indoor tanks
• NP: Natural ponds with supplementation of duckweed (Lemna minor) (Photo 1)  and leaves of Taro (Colocacia esculenta) (Photo 2)

Photo 1. Duckweed (Lemna minor)	Photo 2.  Taro (Colocacia esculenta)

Species of fish:

• ON: Tilapia (Oreochromis niloticus) (Photo 3)
• CC: Cachama (Colossoma macropomu) (Photo 4)

Photo 3. Tiapia (Oreochromis spp)	Photo 4. .Cachama (Colossoma macropomum)

The treatments were applied to 8 plastic tanks in the Aquatic Resources building (Photo 5) and to 8 ponds situated outdoors (Photo 6).

Procedure

The ponds in the NP system were 2*2m in area and 1.5m deep. They were lined with polyethylene sheet to prevent filtration. Biodigester effluent was added to the ponds at weekly intervals equivalent to 240 mg N/m²/day (about 1 liter biodigester effluent/m²/day). The effluent was taken from a “plug-flow” tubular polyethylene biodigester (0.5 m³ liquid volume with 20 days of retention time) charged daily with pig manure (5 kg of fresh manure and 20 litres of water) collected from a nearby  farm. The N content of the effluent was 600 mg/litre with 535 mg/litre as NH₄-N. Duckweed was obtained from a pond managed to optimize duckweed production by application of biodigester effluent. The duckweed was added to the NP ponds in amounts that resulted in the plants covering half the surface of the ponds; Taro leaves were given at the rate of 350g/week per pnd. Stocking rate was 20 fish/pond (5 fish/m²) for both species.

In the IS system, the fish were cultured in plastic (PVC) tanks of capacity 0.5 m³. The stocking density was 50 fish/m³.  Pelleted commercial fish feed was given at 3-5% of LW (DM basis). The water in the tanks was exchanged every day at 7:00 am.

Measurements

The weights and length of the fish were measured before releasing them into the ponds/tanks and at the end of the trial. The pH and ammonia-N were determined weekly in the morning (7:00 am). Temperature of the water was measured every day at 7.00 am, 12 am and 5.00 pm.

Chemical analyses

Feeds were analyzed for N following the method of AOAC (1990) and for DM using a micro-wave oven (Undersander et al 1993). Ammonia-N in the water was estimated by colour generation with a test kit.

Statistical analyses

The data were subjected to analysis of variance  using the General Linear Model (GLM) of the ANOVA option in the Minitab software (MTB 2000). Sources of variation were: species, system, species *system interaction and error.

Results and discussion

Water quality

Water temperature was lower in the intensive (indoor) tanks than in the natural (outdoor) ponds (Table 1). There were no differences in the average pH but ammonia-N was much higher (100 times) in the water in the intensive tanks than in the natural ponds. It is assumed the origin of the ammonia in the intensive system was from the decomposition of the un-ingested feed and the fecal material.

Growth of Tilapia and Cachama

Both species of fish grew faster in weight and length, and weight/length ratio, in the intensive system than in the natural system (Tables 2 and 3 and Figures 1-3). In both systems the Tilapia had better growth performance than the Cachama.

Figure 1. Growth in weight of Cachama and Tilapia in natural and intensive systems	Figure 2. Growth in length of Cachama and Tilapia in natural and intensive systems	Figure 3. Growth in weight/length ratio of Cachama and Tilapia in natural and intensive systems

Natural system

Pich Sophin and Preston (2001) compared 5 species of fish in ponds fertilized with biodigester effluent (117 mg N/m2/day), pig manure (as used in the biodigester) or chemical fertilizer. Daily growth rates of Tilapia were 0.499 g and 0.0405cm resulting in a weight/length increase of 12.3. These results were slightly superior to those in the present experiment, especially for the weight/length ratio. The application of effluent N was lower (117 mg N/m²/day) in the experiment of Pich Sophin and  Preston (2001) than in our study (240mg N/m²/day), and the fish density was less (2 fish/m²); also mixed cultures were used by Pich Sophin and Preston (2001). In terms of net fish yield (kg/ha/day) the results were similar (17 kg in our study compared with 15 kg for Pich Sophin and Preston 2001).  Growth rates in the natural system in our experiment were better than those reported by Edwards et al (1988) in earthen ponds fertilized with biodigester effluent and with pelleted feed supplement (range in weight gain with 5 Tilapia/m² was  0.15 to 0.23g/day).

Results from two experiments with Tilapia grown in a natural system, compared with the present study (Table 4), indicate comparable findings.

Intensive system

Nile tilapia (Oreochromis niloticus) were introduced to China in the late '70s. The rate of development was extremely rapid (Figure 4) approaching 1 million tonnes annually by 2003. In the main,  intensive methods are used with stocking rates of 3 -3.7 fish/m2 and high protein supplementary feed (28-35% crude protein) at 3 to 6% of live weight. Net yields in a 200-240 day cycle were reported to  be 15 to 20 tonnes/ha (Lai Qiuming and Yi No date). In our study with 5 fish/m^2, given pelleted feed at 3-5%  of live weight  the calculated net fish yield would have been 12.2 tonnes/ha assuming the growth rate of the Tilapia (1.22 g/day) would be maintained over a production cycle of 200 days.

Figure 4. Annual production of tilapias in China (from Lai Qiuming and Yang Yi [No date])

Feed costs of Intensive and Natural systems

Estimates of feeds offered and DM feed conversion ratios for the Tilapia in the intensive and natural systems (Table 5) show major differences with much higher intakes of DM in the intensive than in the natural system. Although growth rates were lower in the natural system (0.358 g/day) than in the intensive system (1.22 g/day), supplement intakes were much lower with the result that the estimated DM feed conversion in the natural system was only one half of that in the intensive system, The cost of the fish feed was USD 0.35/kg and the value of the net fish yield about USD 1.00/kg thus with a feed conversion of 1.58 the income over feed would be about 0.50 USD per 1 kg of fish. In the natural system, it is assumed the Taro and duckweed are grown on the farm and have no direct cost, as family labour would be used to grow and harvest them. In this case the estimated return would be about twice that in the intensive system.

Conclusions

• Both Tilapia and Cachama grew faster in weight and length, and in weight/length ratio, in the intensive system than in the natural system.

• In both systems the Tilapia grew faster than the Cachama.

• Less supplement DM was required per unit live weight gain for the Tilapia in the natural than in the intensive system, with the implication that despite the slower growth rates, the economic analysis would favour the former.

Acknowledgements

The authors would like to thank the Swedish International Development Agency (Sida) and the Norwegian Programme for Development, Research and Higher Education (NUFU) for the financial support for this research. The research forms part of the requirement by the senior author for the MSc degree from Cantho University. The administration and teaching staff of An Giang University are gratefully acknowledged for providing resources and advice for conducting the research.

References

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Received 7 January 2011; Accepted 1 March 2011; Published 1 April 2011

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