Effect of biodigester effluent, duckweed and leaves from Taro (Colocacia esculenta) on growth of Tilapia (Oreochromis niloticus) in open ponds

Tick Nouanthavong and T R Preston*

National Agriculture and Forestry Research Institute (NAFRI),
Vientiane, Lao PDR
tick_a@hotmail.com
* Finca Ecológica TOSOLY, AA 48 Socorro, Colombia

Abstract

Leaves from Taro (Colocacia esculenta) and Duckweed (Lemna spp) were compared as supplements for Tilapia (Oreochromis niloticus) grown in open ponds fertilized with biodigester effluent or not fertilized.  The design was a 3*2 factorial arrangement with 3 replications.  Fresh duckweed (Lemna minor) was grown in adjacent ponds fertilized with biodigester effluent. Taro leaves (Colocacia esculenta) were harvested from natural stands in the Centre. Both supplements were given ad libitum. The Tilapia had an average starting weight of 2.52 g and length 5.3 cm. The density was 5 fish/m². The 18  ponds were each 3*2m and 1 m depth. The biodigester effluent was taken from a tubular polyethylene plug-flow biodigester charged with pig manure. The quantity applied was 520 mg N/pond/day.

Growth rates were four-fold higher for Tilapia supplemented with duckweed compared with Taro leaves or no supplement; and were 22% higher in ponds fertilized with biodigester effluent compared with no fertilizer. There were no benefits from feeding Taro leaves. Survival was high on all treatments (98-99%). Values for pH, ammonia and nitrous dioxide were higher in ponds fertilized with biodigester effluent than in unfertilized ponds.

Key words: ammonia, feed conversion, nitrous oxide, pH, survival, temperature

Introduction

In an earlier paper (Nouanthavong and Preston 2011) we stressed "the 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 conclusion from a preliminary 60 day trial with Tilapia and Cachama was that, although both species grew faster in tanks with artificial feed, than in open ponds fertilized with biodigester effluent and supplementary duckweed, 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. The present study aimed to provide further information on the response of Tilapia to supplements of duckweed and taro leaves, in open ponds with and without fertilization from biodigester effluent.

Duckweed (Lemna minor) has been used successfully as a complete feed for fish (Skillicorn et al 1993; Leng et al 1995) and as the sole source of protein for pigs (Rodríguez and Preston 1996a). It grows well in earthen ponds and in ponds lined with concrete or polyethylene film (Rodríguez and Preston 1996b). It responds with linear increases in biomass yield and crude protein content when fertilized with biodigester effluent (Rodríguez and Preston 1996b; Dang Thi My Tu et al 2011).  The leaves of several members of the Araceae plant family  (eg: Colocacia esculenta, Xanthosoma sagittifolium) are also rich in crude protein which is highly digestible and with good biological value in pigs (Rodríguez et al 2009; Manivanh and Preston 2011).  However, apaprt from our earlier report (Nouanthavong and Preston 2011) there appears to be no information on its potential value as a supplement for fish.

Hypothesis

• Tilapia will grow well in natural pond systems when biodigester effluent is used as fertilizer to stimulate growth of plankton
• Growth rates of Tilapia will be increased when they are also fed fresh leaves of Taro and duckweed

Objective

To measure the growth performance of Tilapia (Photo 1) using biodigester effluent as fertilizer and Taro leaves (Photo 2) and Duckweed (Photo 3)  as protein supplements.

Materials and Methods

Location and climate

The experiment was carried out at the Nangtang hatchery belonging to the Living Aquatic Resource Research Center. The site is 15 km from Vientiane Capital in Sikottabong District, Vientiane, Lao PDR. The experiment was started in January 2011 and finished in July 2011. The climate in Lao PDR is tropical with an average daily temperature of 31 °C and an average annual precipitation of 1500 mm, about 75% of which occurs in the monsoon season (May to October) (Kottelat 2001). 

Treatments and experimental design

Six treatments in a Completely Randomized Design (CRD) were arranged as a 3*2 factorial with 3 replications (Table 1). The factors were:

Feed supplement

• NS: No supplement
• TL: Taro leaves
• DW: Duckweed

Fertilizer

• E: With biodigester effluent

• NE: No fertilizer

Table 1. Experimental layout
1	2	3	4	5	6
DWNE	NSE	NSE	NSNE	NSNE	DWE
7	8	9	10	11	12
NSE	TRE	TRNE	DWE	TRE	DWNE
13	14	15	16	17	18
TRNE	DWNE	NSNE	TRNE	TRE	DWE

Ponds, fish and management

The 18 ponds were 2m x 3m in area and 1 m deep, lined with plastic film to avoid water leakage through the sandy soil (Photo 4). Ten days before stocking with fish, quick-lime (CaO) was applied to the bottoms of all ponds at the rate of 100 g/m². This was done  to eliminate parasites and pathogenic organisms and to increase the pH (Pich Sophin and Preston 2001).  Two ponds were managed solely to produce the duckweed used in the experiment (Photo 5).

Photo 4. Arrangement of the ponds	Photo 5. Two ponds dedicated to the production  of duckweed

The Tilapia fingerlings had an average initial weight of 2.52 g and a length of 5.3 cm. They were put first in a nursery pond to adapt them to the local conditions. During this time they had free access to duckweed and taro leaves. After 2 weeks they were allocated to the treatment ponds at the rate of 30 fish per pond, giving a stocking rate of 5 fish/m².

Biodigester

A plug-flow tubular polyethylene biodigester was installed to supply the effluent for the duckweed ponds and for the fish ponds. It had a length of 6 m and a diameter of 1m. The liquid volume was 2 m². It was charged with fresh pig manure from the piggery adjacent to the project site. The charging rate was 180 litres daily of a mixture containing 4% of DM derived from the pig manure (about 20 kg pig manure [25% DM] and 160 litres water).

Photo 6. The tubular polyethylene biodigester	Photo 7. The inlet to the biodigester	Photo 8. Collecting the effluent

The duckweed pond

Duckweed was first collected from a waste water surface (Photo 9) and washed thoroughly with fresh water prior to introduction to the two ponds dedicated to duckweed production. These were fertilized with biodigester effluent at the rate of 20 litres daily (assumed N concentration was 500 mg N/litre of effluent) http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGA/AGAP/FRG/recycle/default.htmIn

Taro leaves

Taro leaves were harvested from the edges of the ponds in the Nangtang hatchery where it grows naturally.

Feed and feeding

The Taro leaves were harvested once per week and fed ad libitum as the whole leaf, which floated  on the water surface (Photo 10). Duckweed was harvested daily from the two dedicated duckweed ponds. and also  fed ad libitum (Photo 10). The actual quantities offered of Taro leaves and duckweed were based on the observed rates of consumption. The biodigester effluent was added at the rate equivalent to 150 kg N/ha/year (about 2 litres/pond/day).

Photo 9. Collectung duckweed from a waste water water surface	Photo 10. Feeding Taro leaves	Photo 11. Feeding the duckweed

Data collection

Fish weight and length

The average weight of the fish was recorded before releasing them into the ponds and at the end of 150 days of experiments.  A random sample of fish (n = about 10) was weighed and measured every 30 days. The growth in weight was calculated from the linear regression of weight on time, disregarding the weight from 0 to 30 days, as this was considered to be an adaptation phase (see Figure 2).

Feed intake

The amounts offered of duckweed and taro leaves were recorded. There were no residues as fresh feed was only offered after the previous feed had been consumed.

Water quality

pH, ammonia-N and NO₂  in pond water were determined at 7:00 am two times per month using colorimetric test kits (Photos 12-14). Temperature was measured every day, three times at 7.00 am, 12:00pm and 5.00 pm.

Photo 12.  The colorimetric kit to measure pH	Photo 13. The colorimetric kit to measure nitrite	Photo 14. The colorimetric kit to measure ammonia-N

Samples of effluent were taken weekly before application to the fish pond for determination of pH, DM, OM, N and Ammonia–N. Details of the analytical methods employed are in San Thy et al (2003). Samples of taro leaves and duckweed were taken weekly for analysis.

Chemical analyses

Feeds were analyzed for N following the method of AOAC (1990) and DM using the micro-wave ovenmethod (Undersander et al 1993). pH, NO₂ (Nitrite) and ammonia-N in the pond water were estimated by colorimetric test kits (Photos 15-17).

Statistical analyses

The data were subjected to analysis of variance by using the General Linear Model (GLM) option of the ANOVA program in the MINITAB  (2000) software. The sources of variation in the model were supplements, effluent, interactiuon effluent*supplement and error.

Results and discussion

The protein content of the duckweed was higher than for the leaves of Taro (Table 2). 

The weight gain of the Tilapia was four-fold higher when they were supplemented with duckweed compared with Taro leaves or no supplement (Table 3; Figure 1). The growth rate of the Tilapia (0.96 g/day) in ponds supplemented with duckweed and fertilized with effluent (Table 4) was similar to that (0.95 g/day) reported by Yen Nhi and Preston (2011) in an identical system in Vietnam with the same stocking rate of 5 fish/m². With a lower stocking rate of 3 fish/m² , the growth reported by these authors was 1.32 g/day.  There was no advantage in giving Taro leaves as compared with no supplement.

The Tilapia  gained weight 22% faster when the ponds were fertilized with biodigester effluent. On effluent only,  the gain of 0.18 g/day was lower than the 0.27 g/day reported by San Thy et al (2008) for Tilapia stocked at a lower density of 2 fish/m2. These authors reported that growth rates were doubled to 0.43 g/day when the effluent was from biodigesters managed with a longer hydraulic retention time (30 compared with 20 days).  The moderate response to fertilization with biodigester effluent may have been the consequence of the level of N that was applied. According to Knud-Hansen et al  (1991) and Lin et al (1997) the optimum input of nitrogen for fish culture is 4 kg N/ha/day or 400 mg N/m^² per day. This level (equivalent to 1460 kg N/ha/year) is almost ten times greater than the amount applied in our experiment (150 kg N/ha/year).

The daily DM intake was three times greater for duckweed than for the Taro leaves, which explains to a major degree the three-fold greater growth rate for the Tilapia fed duckweed compared with the Taro leaves. DM feed conversion appeared to be similar on duckweed as on Taro leaves, but this comparison was confounded by the contribution from the effluent. When the growth rates were corrected for the effect of the effluent (weight gain on [duckweed / Taro leaves]  - weight gain of Tilapia in [effluent-fertilized ponds]), the DM feed conversion changed dramatically, increasing to 18.4 for the Taro leaves treatment compared with 1.08 for Tilapia supplemented with duckweed. The feed conversion ratios on the duckweed with or without correction for effects of the natural feed supply (0.76 to1.08) were much better than was reported in Brazil (Tavares et al 2008) for Tilapia managed in open ponds and supplemented with dried duckweed containing 39% crude protein (DM FCR 3.0) or a commercial fish feed of 40% crude protein (DM FCR 1.6).  The weight gains in our experiment for fresh duckweed (0.95 g/day) were also higher than those (0.36 g/day on fish feed compared with 0.22 g/day on dried duckweed) recorded by Tavares et al (2008).

 

Figure 1. Effect of biodigester effluent and supplementation with duckweed or Taro leaves on weight gain of Tilapia raised in open ponds	Figure 2. Growth curves of Tilapia raised in open ponds fertilized with biodigester effluent (E) or no fertilizer (NE), and supplemented with duckweed (DW), Taro leaves (TR) or not supplemented (NS)

 Water quality

There were differences in water temperature among supplementation treatments but not between ponds fertilized or not with effluent (Table 5). However the differences were small.

The values for pH, and esppecially ammonia (Figure 3), were higher in ponds fertilized with biodigester effluent than in ponds not fertilized (Table 6) and tended (P=0.10) to be higher also for nitrous oxide. However, all the values were within the range considered suitable for fish culture (Boyd 1990).

Figure 3. Effect of fertilization with biodigester effluent on ammonia concentration in the ponds

Conclusion

• The weight gain of  Tilapia was four-fold higher (0.96 g/day)( when they were supplemented with duckweed compared with Taro leaves or no supplement; and was 22% higher in ponds fertilized with biodigester effluent compared with no fertilizer.

• There were no benefits from feeding Taro leaves.

• DM feed conversion was much superior on the duckweed supplement, ranging from 0.76 to 1.08, the latter being the adjusted value after allowing for the growth rate supported by the natural food chain in the ponds.

• Survival was high on all treatments (98-99%).

• Values for pH, ammonia and nitrous dioxide were higher in ponds fertilized with biodigester effluent than in unfertilized ponds.

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 Living Aquatic Resource Research Center (LARReC) belonging to National Agricuture and forestry Research Institute (NAFRI) was the supporting location for the experiment.

References

AOAC 1990 Official Methods of Analysis Association of Official Analytical Chemists 15^th Edition (K Helrick editor) Arlington pp 1230

Boyd C E 1990 Water quality in ponds for aquaculture. Alabama agriculture experiment station, Auburn University. Birmingham Publishing Co. Birmingham, Alabama. First printing 5M, December 1990.

Dang Thi My Tu, Nguyen Thi Kim Dong and Preston T R 2011 Effect on duckweed composition of different levels of biodigester effluent in the growth medium and of transferring nutrient-rich duckweed to nutrient-free water.  Workshop on Reducing Greenhouse Gas Emissions from Livestock and Soils (Editors: Reg Preston and Sisomphone Southavong). National Institute of Animal Science, Hanoi, 14-15 November 2011. httm://www.mekarn.org/workshops/GHG-CC/mytu.htm

Fasakin E, 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

Gaigher I G, Porath D and Granoth G 1984 Evaluation of duckweed (Lemna gibba) as feed for tilapia (Oreochromis niloticus X O. aureus) in a recirculating unit. Aquaculture 41: 235-244.

Knud-Hansen C F, McNabb C D and Batterson T R 1991 Application of limnology for efficient nutrient utilization in tropical pond aquaculture. Proceedings of the International Association of Theoretical and Applied Limnology 24:2541-2543.

Kottelat M 2001. Fishes of Laos. WHT Publications, Colombo

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:  http://www.lrrd.org/lrrd/7/1/3.htm

Leng R A (no date) Duckweed; a tiny aquatic plant with enormous potential for agriculture and environment.  FAO Animal Production and Health Paper 143.  http://www.utafoundation.org/DWLenghtm/Duckweed3.htm

Lin C K, Teichert-Coddington D R, Green B W and Veverica K L 1997 Fertilization regimes. In: H.S. Egna and K.L. Boyd (Editors), Dynamic of pond aquaculture. CRCP Press, Boca Raton/ New York.

Manivanh N and Preston T R 2011 Taro (Colocacia esculenta) silage and rice bran as the basal diet for growing pigs; effects on intake, digestibility and N retention. Livestock Research for Rural Development. Volume 23, Article #55. http://www.lrrd.org/lrrd23/3/noup23055.htm

Minitab 2000 Minitab Release 13.31 for windows, Windows* 95/98/2000/xp. Minitab Inc., State College Pennsylvania, USA.

Nouanthavong Tick  and Preston T R 2011 Comparison of natural pond system with an intensive (indoor) system for raising Cachama (Colossoma macropomu) and Tilapia (Oreochromis niloticus). Livestock Research for Rural Development. Volume 23, Article #100. http://www.lrrd.org/lrrd23/4/tick23100.htm

Pich Sophin and Preston T R 2001 Effect of processing pig manure in a biodigester as fertilizer input for ponds growing fish in polyculture.  Livestock Research for Rural Development. (10) 6:  http://www.lrrd.org/lrrd13/6/Pich136.htm

Rodríguez Lylian and Preston T R 1996a Comparative parameters of digestion and N metabolism in Mong Cai and Mong Cai*Large White cross piglets having free access to sugar cane juice and duck weed. Livestock Research for Rural Development. (8) 1:  http://www.lrrd.org/lrrd8/1/lylian.htm

Rodríguez Lylian and Preston T R 1996b 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

Rodríguez Lylian, Peniche Irina, Preston T R and Peters K 2009 Nutritive value for pigs of New Cocoyam (Xanthosoma sagittifolium); digestibility and nitrogen balance with different proportions of fresh leaves and soybean meal in a basal diet of sugar cane juice. Livestock Research for Rural Development. Volume 21, Article #16. http://www.lrrd.org/lrrd21/1/rodr21016.htm

San Thy and Preston T R 2003  Effluent from biodigesters with different retention times for primary production and feed of Tilapia (Oreochromis niloticus). Livestock Research for Rural Development 15 (9). http://www.lrrd.org/lrrd15/9/sant159.htm

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

Skillicorn P, Spira W and Journey W 1993  ’’Ducuckweed  Agriculture. The New Aquatic Farming System for Developing countries” The World Bank. Washington DC, USA.

Tavares Flávia de A, Rodrigues João Bosco R, Machado Fracalossi D, Esquivel J and Roubach R 2008 Dried duckweed and commercial feed promote adequate growth performance of tilapia fingerlings. Biotemas 21 (3): 91-97

Undersander D, Mertens D R and Theix N 1993 Forage analysis procedures. National Forage Testing Association. Omaha pp 154.

Yen Nhi N H and Preston T R 2011 The growth and economics of integrated culture of Tilapia (Oreochomis niloticus) and Common carp (Ciprinus carpio) in an indoor intensive system with earthworms as feed and in natural ponds fertilized with biodigester effluent and supplemented with duckweed. Livestock Research for Rural Development. Volume 23, Article #161. http://www.lrrd.org/lrrd23/7/nhi23161.htm

Received 1 January 2012; Accepted 21 January 2012; Published 7 February 2012

Go to top