Effect of stocking density and fertilization on the growth performance of Nile tilapia (Oreochromis niloticus) fed rice bran, water spinach and duckweed in pond and paddy field

Sen Sorphea, Torbjorn Lundh*, T R Preston**, Khieu Borin

CelAgrid (Centre for Livestock and Agriculture Development), P.O Box 2423, Phnom Penh 3, Cambodia sorphea_sen@yahoo.com
*Department of Animal Nutrition and Management, Swedish University of Agricultural Science,
Uppsala, Sweeden
** University of Tropical Agriculture Foundation, UTA - TOSOLY Finca Ecológica,
AA # 48, Socorro, Santander, Santander del Sur, Colombia

Abbreviations

ADG Average daily weight gain

CP Crude protein

DM Dry matter

N Nitrogen

FE Feed fertilize with biodigester effluent

FNE Feed no fertilize with biodigester effluent

EF Effluent from biodigester with feed supplement

ENF Effluent from biodigester without feed supplement

1. Introduction

The natural fish harvest has declined during the last 10 years in Cambodia due to illegal fishing and environmental changes. This has a significant affect on the livelihood of Cambodian people whose main protein source is deriving from fish. At present, much effort from government, development institutions and the private sector has been given to the development of aquaculture in order to match the shortfall of fish protein fish human consumption. It has been observed that around Phnom Penh city and else where with access to water and ponds fish culture has increased. Farming of common carp, silver carp, silver barb, tilapia and catfish is encouraged by government and development organizations so that farmers in the rural area can have fish for their own consumption and income generation.

Fish culture in the rice field is especially interesting as a method for maximizing land use, combining the production of both rice and fish. Fish culture in the rice fields is mainly concentrated in Southeast Asia where it has been known for centuries. A number of advantages are obtained by applying the rice-fish cultivation. The presence of fish in a rice field generally increases the rice yield by 10 to 15% (Hilbrands et al 2004). Fish is a source of protein and by integrating production with rice food security is improved. In addition, raising fish contributes to the improvement of public health because they can eat insects like mosquitoes. Raising fish in a rice field is also a biological way of reducing weeds, insects, snails and some rice diseases. This is a safe and cheap alternative to using chemical pesticides to control insects and algae. In areas where rice production is not profitable in all seasons, fish production forms an alternative source of income from the field (Hilbrands et al 2004).

The major factors that influence the economics of fresh water fish production in pond culture are:

When fish are raised in the rice field, the same factors apply but in addition there are the direct and indirect effects of the fish on the yield of rice.

2. Objectives

· To study the effect of stocking density and supplementation on the growth performance of tilapia raised in rice paddies .

3. General discussion

3. 1. Tilapia

Thr advantages of using Tilapia are that this species can digest natural food organisms, such as plankton, some aquatic macrophytes, planktonic and benthic aquatic invertebrates, larva fish, detritus, and decomposing organic matter. They are thus well suited to systems which depend to a major extent on stimulating the natural feed chain and use of vegetative supplements such as duckweed and water spinach.

3. 2 Biodigester effluent as fertilizer for fish ponds

The potential for using animal wastes in fish culture has been demonstrated for many years in China, where animal manure has been used as the main fertilizer in fish culture. Processing of manure by anaerobic biodigestion results in the production of biogas which is used as fuel mainly for cooking,. and effluent which contains all the plant nutrients present in the original manure while the greater part of the nitrogenous compounds is converted to ammonium salts (San Thy and Preston 2003). This ionization of the nitrogenous fraction has been shown to improve the fertilizer value of the effluent compared with the original manure The biomass yields and crude protein content of duckweed and cassava foliage were increased when biodigester effluent rather than the manure put into the biodigester was used as fertilizer (Le Ha Chau 1998a,b). Similar positive results have been reported for the use of biodigester effluent in fish culture. Pich Sophin and Preston (2001) reported that tilapia, silver carp, bighead carp, silver barb and Mrigal grew faster in ponds fertilized with effluent than with urea-DAP or manure. Increased productivity in poly-culture fish ponds when biodigester effluent was the fertilizer rather than raw manure was also reported by Ding Jieyi and Han Yujin (1983). Yields of fish were increased by 26% when the effluent was applied compared with the original manure.

Surprisingly, there was no effect of biodigester effluent in the experiment reported in Paper I. The reason may have been the over-riding effect of the supplementation with duckweed, water spinach and rice bran, which besides serving as direct feed to the fish would also have acted partially as fertilizer for the ponds.

3. 3. Duckweed and water spinach

Duckweed is a small floating aquatic plant that grows very well on stagnant ponds and is commonly found throughout tropical countries (Leng et al 1995). Crude protein yields of between 6 and10 tonnes/ha/yr have been recorded when the N content in the water was in the range of 10 to 30 mg/litre (Nguyen Duc Anh 1997). Not only the yield but also the crude protein of duckweed responds to the nutrient content of the water, increasing from 15% in DM with 10 mg N/litre to 40% crude protein in DM with 60 mg N/litre (Rodríguez and Preston 1996). Many trials have been carried out using duckweed as the major feed to raise fish, with good results (Journey et al. 1991). Fasakin et al (1999) found that duckweed meal (from Spirodela polyrrhiza) could replace up to 30% of the total diet of the blue tilapia (Oreochromis niloticus) Hasan and Edwards (1992) grew tilapia in static water concrete tanks and found that the fish slowly consumed Spirodela polyrrhiza while Lemna perpusilla was rapidly consumed.

Water spinach and duckweed were compared as supplements to a polyculture (Tilapia, Silver carp and Migril) in ponds fertilized with biodigester effluent at 120 kg N/ha (San Thy et al 2008). Net fish yields were 1888 and 2493 kg/ha for water spinach and duckweed compared with only 848 kg/ha when only effluent was used.

In experiment 2 in Paper I, supplementation with a combination of duckweed, water spinach and rice bran (25, 25, 50% DM basis) increased the net fish yield from 81.4 to 122 kg/ha; however, the system was different from that described by San Thy et al (2008) in that the fish (Tilapia) were cultivated in a rice paddy.

3.4 Fish stocking density

There appear to be no studies on the effect of fish stocking density in culture systems of the kind described in Paper I. In the present study, when the Tilapia were raised in 10m² ponds, net fish yield was increased from 1466 to 2248 kg/ha; however, at the same time, the fish survival rate declined from 78 to 60%. In the rice paddy system, increased stocking density from 3 to 5 fish/m² also increased net fish yield (from 80 to 123 kg/ha) but this was also associated with a reduction in survival rate from 66 to 42%. The indirect effect of a decrease in survival rate was to increase the feed availability to the survivors which grew faster such that at the end of the experiment, the total fish weight was greater, although numbers were smaller in the treatments with lowest survival rate.

3. 5 Integrated Rice-Fish systems

Most studies on integrated rice-fish system have employed stocking densities of between 1500 and 6000 fish/ha of rice paddy. In the study with no supplement (Rothius 1998), the net fish yield increased linearly (from 60 to 180 kg/ha) as the fish density was increased from 1500 to 6600/ha. In the report of Bocek (no date), the increase in fish density from 1500 to 4500/ha resulted in the net yield increasing from 500 to 1000 kg/ha, but in this case the fish were supplemented with soybean, copra meal and rice bran.

In the study reported in Paper 1, the net fish yield increased from 80 to 123 kg/ha when the fish density increased from 3300 to 5500 fish/ha.

4. Conclusion

5. Acknowledgement

The authors are grateful to the MEKARN program, financed by Sida (Swedish International Development Agency)) for supporting this study.

6. References

Ding Jieyi and Han Yujin 1983: Comparative studies on the effects of fresh pig manure and anaerobically fermented

Fasakin E A, Balogun A M and Fasuru B E 1999 Use of duckweed, Spirodela polyrrhiza, L. Schleiden, as a protein feedstuff in practical diets for tilapia, Oreochromis niloticus L. Aquaculture Research 30:313-318

Hasan M S and Edwards P 1992 Evaluation of duckweed (L. perpusilla and S. polyrrhiza) as feed for Nile tilapia (Oreochromis niloticus). Aquaculture 104:315-326

Journey W K, Skillicorn P and Spira W 1991 Duckweed Aquaculture - A New Aquatic Farming System for Developing Countries. The World Bank. 76pp. Washington DC)

Leng R A, Stambolie J H and Bell R 1995: Duckweed - a potential high-protein feed resource for domestic animals

and fish. Livestock Research for Rural Development (7) 1 Livestock Research for Rural Development. (7) 1 http://www.lrrd.org/lrrd7/1/3.htm

Le Ha Chau 1998a Biodigester effluent versus manure from pigs or cattle as fertilizer for production of cassava foliage (Manihot esculenta). Livestock Research for Rural Development. (10) 3 http://www.lrrd.org/lrrd10/3/chau1.htm

Le Ha Chau 1998b Biodigester effluent versus manure, from pigs or cattle, as fertilizer for duckweed (Lemna spp.) Livestock Research for Rural Development. (10) 3 http://www.lrrd.org/lrrd10/3/chau2.htm

Nguyen Duc Anh and Preston 1997 Effect of management practices and fertilization with biodigester effluent on biomass yield and composition of duckweed. Livestock Research for Rural Development: 9 (1) http://www.lrrd.org/lrrd9/1/anh91.htm

Rodriguez L and Preston T R 1996 Use of effluent from low-cost plastic biodigesters as fertilizer for duck weed ponds Livestock Research for Rural Development: 8 (2) http://www.lrrd.org/lrrd8/2/lylian2.htm

Rothuis A 1998 The effect of rice seeding rate on rice and fish production in direct-seeding rice-fish culture. Page 43.

Chapter 7: Polyculture of Silver Barb, Puntius Gonionotus (Bleeker), Nile Tilapia, Oreochronis Niloticus (L) and Common Carp, Cyprinus Carpio (L) in Vietnamese rice fields: 2. Fish production parameters. Page 90.

San Thy and T R Preston 2003 Effluent from biodigesters with different retention times for primary production and feed of Tilapia (Oreochromis niloticus) Livestock Research for Rural Development: 15 (9) 2003

San Thy, Khieu Borin, Try Vanvuth, Pheng Buntha and Preston T R 2008 Effect of water spinach and duckweed on fish growth performance in poly-culture ponds. Livestock Research for Rural Development. Volume 20, Article #16. http://www.lrrd.org/lrrd20/1/sant20016.htm