Effect of water spinach and duckweed on fish growth performance in poly-culture ponds

San Thy, Khieu Borin, Try Vanvuth, Pheng Buntha and T R Preston*

CelAgrid, UTA Cambodia,
santhysimon@yahoo.com
* Fundación para la Producción Agropecuaria Tropical Sostenible Capitulo Colombia,
UTA-TOSOLY - Finca Ecológica, AA 48 Socorro, Colombia

Abstract

A total of 360 fingerlings were distributed to twelve ponds of 10 m² each. The composition of fish in a pond was 40%, 35% and 25% of tilapia (Oreochromis niloticus), common carp (Cyprinus carpio) and mrigal (Cirrhinus mrigal) respectively. Treatments were effluent (E), effluent plus water spinach (EWS) and effluent plus duckweed (EDW). The level of effluent applied was 120 kg N ha^-1. The water spinach and duckweed were given daily at 3 to 5% DM of fish bodyweight from fingerling stage to 120 days old respectively.

The water quality (pH, water transparency, water temperature and dissolved oxygen) were similar in all treatments. The survival rate was similar for all species (88.3%, 90.6 and 92.4 % of common carp, mrigal and tilapia respectively) however lower survival rate was in ponds fed duckweed. The daily weight gain was significantly difference between species and supplements except the duckweed ponds. The total daily weight gain was 6.17, 15.2 and 21.2 kg ha^-1 day^-1 (P=0.012, SE±2.74) resulting a total yield of 1,450, 2,470 and 3,120 kg ha^-1 per 4 months (P=0.007, SE±276) for E, EWS and EDW respectively.

It is concluded that duckweed and water spinach can be used as a supplement to poly-culture fish although fish gained better with the supplement of duckweed.

Keywords: biodigester effluent, Cirrhinus mrigal, Cyprinus carpio, duckweed, fish, polyculture, pond, Oreochromis niloticus, water spinach

Introduction

Fish constitutes more than 70% of the total animal protein intake of the Cambodians. Fishery contributes from 3.2 to 7.4 percent to the gross domestic product (GDP) although fish caught from natural water such as lakes and ponds has declined from 120 000 - 130 000 tones in the 1960s (about 25kg per capita) to 75 000 tones in the 1990s (about 10-13 kg per capita) while the population of Cambodia is reaching almost 14 million in 2006 and continues to increase on average at about 2.4 percent. Although it is still slow, the aquaculture has increased from 1610 tonnes in 1984 to 15000 tonnes in 1999 (Nao Thouk 1999).  

The aquaculture systems practiced in Cambodia are: (i) cages culture and (ii) ponds culture. The fish production can be monoculture and poly-culture. However, to optimize the use of natural resources, the integration of animals, crops and fish is an ideal strategy. In recent years, research has been promoted in Cambodia, giving attention on the role of biodigesters as a key component of the farming systems. The recycling of waste gives additional value to both human and animal wastes through gas production, produce good quality of organic materials and the control of pathogens. The effluent from the biodigester has been used to produce plankton for fish.HHHH

Duckweed has been reported to have good balance of amino acids comparable to milk (Leng et al 1995). Duckweed is a good quality when it was harvest in the ponds and canals nearby the houses due to the availability of nutrients. Duckweed grown naturally in ponds and canals with poor nutrients grow slowly with long root systems and has poor protein content.

Water spinach is available naturally in the rainy season or it can be planted in the rainy and dry seasons. The two types of water spinach; land and aquatic, are commonly cultivated by farmers. When water is not a constraint factor, aquatic water spinach has the capacity to produce foliage for longer period. Aquatic water spinach produce up to 40 ha^-1 cut^-1 when applied 200 kg of nitrogen ha^-1 year^-1 (CelAgrid, unpublished data).

The purpose of the present study is to investigate the supplement of the water spinach and duckweed on the growth performance of the tilapia, common carp and Indian carps kept in poly-culture in the ponds.
 

Materials and methods

Experimental period

The experiment was carried out at the Centre for Livestock and Agriculture Development ‘CelAgrid’ from April 21 to August 20, 2004.

Pond construction and preparation

A total of 12 ponds were excavated with the capacity of 20 m³ each (4 m length x 2.5 m wide and 1 m deep). The ponds were lined with blue plastic to protect from soil erosion and to avoid filtration of water. After paving the blue plastic, water from pond was pumped into all experimental ponds. Lime (CaO) at 200 g/m² was applied at 20 days before stocking with fish, in order to kill parasites and pathogenic organisms if existed and also to increase the pH (Photo 1).

Experimental design

The Completed Randomized Block Design was used. There were 3 treatments: the effluent as control (E), effluent with the supplement of water spinach (EWS), and the effluent with the supplement of duckweed (EDW) and each treatment replicated 4 times.

Stocking density and fish composition

Each pond was stocked with three fish species at a density of 3 fishes per m². The species were tilapia (Oreochromis niloticus), common carp and mrigal (Cirrhinus mrigal). The composition was 40 percent of tilapia, 35% of common carp, and 25% for Mrigal which was equal to 12, 10 and 8 heads (30 fish per 10 m²) of tilapia, common carp and Mrigal respectively.  

Fertilization and feeding

Biodigester effluent

Ponds were fertilized with effluent from a plastic biodigester loaded with pig manure with the rate of 120 kg of nitrogen per ha^-1 year^-1. The chemical composition of the effluent is presented in Table 1.

Feed supplementation

Feed supplementation (water spinach and duckweed) was given twice daily at 8:00 am and 4:00 pm. The feed supplementation was estimated at 5% DM basis of the fish body weight. Duckweed and water spinach were cultivated at CelAgrid. The chemical composition of the feed supplements is presented in Table 2.

Measurements and analyses

The effluent from biodigester was daily sampling and bulked for the weekly analysis of N, OM, Nitrogen, and Ammonia. The quantity of N was calculated before applying into the fish pond. Fish bodyweight and length were measured at 8:00 am in every 20 days before applying the feed or effluent.

The oxygen and pH of the water in the fish pond was measured in every 4 days and each measurement was taken twice at 6:00 am and at 4:00 pm using the DO₂ meter (Model 9150). The water temperature was measured three times weekly at 6:00 am, at 12:00 am and at 5:00 pm using thermometer placing in each pond for 5 minutes. Water quality was also measured at 12.00 am in every 2 days using Secchi disk.

Statistical Analyses

The data were subjected to analysis of variance (ANOVA) by using the General Linear Model (GLM) of the SPSS software (Release 12.0, 2003). Two ways ANOVA is used to determine length and weight of fish, and the descriptive statistic was used to determine the mean, maximum and minimum of effluent fertilizer, water quality parameters and feed.
 

Results and discussion

Water quality

There were no differences on water quality parameters (pH, water transparency, water temperature and dissolved oxygen) among the treatments (Table 3). The average of oxygen concentration was close to the minimum to level recommended by Swingle (1969). Values from 0.3 to 1mg/litre over an extended period were considered to be lethal to fish and from 1mg to 5mg/litre the fish survived, but growth was slow. The pH for all treatments was within the range suggested by Swingle (1969).

Fish survival rate

The survival rate was similar for all species (88.3%, 90.6 and 92.4 % of common carp, mrigal and tilapia respectively). Ponds fed duckweed had the lowest survival rate compare to the control and water spinach ponds and within those ponds supplemented with duckweed common carp and Mrigal had higher mortality rate compare with Tilapia (Table 4). In contrast to the study by Pich Sophin and Preston (2001) where Tilapia had poorer survival rate either in ponds fertilized with urea-DAP, raw cow manure and effluent from biodigester.

Fish growth in length

Fish supplemented with duckweed had largest length disregard fish species (Table 5).  The length was 11.9% and 28.3% for Mrigal and 10.5% and 26.8% for Tilapia and 15.6 and 28.3% larger than EDW and E fish respectively. However, the length of Mrigal was the largest even the control group comparing with other species.

Fish individual weight

Fish grew faster in the pond supplemented with duckweed followed by those supplemented with water spinach (Table 6). Similar result was also found in Bangladesh where they fed duckweed to Mrigal (William et al 1991). Duckweed was the appropriate choice to be used as supplement for the small-scale aquaculture as it can be harvested from the natural ponds or canals close to houses in the rainy season. The natural ponds and canals are dried up in the dry season in this case an artificial pond managed by farmers could play the role to produce good quality duckweed.

Mrigal among the three species had the highest final weight disregard the feed supplement. After 120 days, the weight of Mrigal was 59.2% and 200% in the control pond, 53.9% and 198% in the EWS ponds and 59.4 and 62.1% higher than Tilapia and common carp respectively. The weight of Tilapia in the control pond of the present experiment was similar to the study reported by Pich Sophin and Preston (2001) where they used effluent from biodigester to fertilize Tilapia pond.

Daily weight gain

The daily weight gain was significantly difference between species and supplements except the duckweed ponds (Figure 1). Mrigal grew faster in the all treatments compare with other species and for all species kept in ponds providing only effluent from biodigester at the rate of 1 kg ha^-1 day^-1 resulted poor growth. Knud-Hansen et. al., (1991) and Lin et. al., (1997) recommended 4 kg ha^-1 day^-1 as the optimum level for fish kept in the pond and it is four times higher than the rate applied of the present experiment. Pig manure loaded in an anaerobic biodigester, before applying in the ponds stocked with poly-culture of fish, resulted in a daily growth 0.5 g day^-1 for tilapia (Pich Sophin and Preston 2001). However, other study using biodigester effluent with the supplement of commercial feed, the daily weight gain was in a range of 0.15-0.23g day^-1 fish^-1 (Edwards et al 1988). Thus the daily weight gain of the present study is quite similar the above studies. As feed supplement used in the present study is available in the rural areas, then it is ideally to give the supplement to fish to be able to get better harvest.

Total yield of fish

The total daily weight gain (P=0.12), total yield (0.007) and net yield (P=0.008) were significantly increased with the supplement of duckweed and water spinach (Table 7). The net yield of fish was 1.2 and 1.9 times for EWS and EDW respectively higher than fish kept in E ponds. The result from our study on fish kept on E ponds is in the agreement with Pich Sophin and Preston (2001) who reported that the fish poly-culture fertilized with effluent from biodigester got an increase of 55% net fish. The explanation that the yield of fish in EDW ponds was better than fish kept in EWS and E ponds because duckweed protein has a better array of essential amino acids than most vegetable proteins and more closely resembles animal protein (Hillman and Culley 1978). Duckweed is converted efficiently to liveweight by certain fish including carp and tilapia (Robinette et al 1980; Hassan and Edwards 1992). The total yield of fish supplemented with duckweed was 3.1 tons ha^-1 per 4 months which is close to the figure reported by Journey et al (1993) that fish supplemented only with well managed and fertilized duckweed, got an average yield at around 10 tons ha^-1 year^-1 annually.   

Conclusions

• Duckweed and water spinach can be used as a supplement to poly-culture fish although fish gained better with the supplement of duckweed.

  
  

• As a strategy for farmers in rural community, they can use duckweed in the rainy season where it is naturally available but good quality duckweed should be harvested from canals and ponds close to houses.

  
  

• Water spinach grown on land can be planted and used as supplement to fish in the dry season.

Acknowledgements

 This paper was first published in the Cambodia Journal of Agriculture, January-June 2006, Volume 7, Number 1 page 12-16 in hard copy. As this Journal is not easily accessible for readers outside Cambodia, the authors requested LRRD to publish this article electronically for a wider readership.

The authors express their appreciation to LRRD for this opportunity. They also thank the Cambodian Agricultural Research Fund AusAid/ACIAR for the financial support to carry out the study.

References 

Edwards P, Polprasert C, Raput V S and Pacharaprakiti C 1988 Integrated Biogas Technology in the Tropics 2. Use of Slurry for Fish Culture. Waste management and research.

Hassan M S and Edwards P 1992 Evaluation of duckweed (Lemna perpusilla and Spirodela polyrhiza) as feed for Nile Tilapia (Oreochromis niloticus). Aquaculture 104:315-326

Hillman W S and Culley D D 1978 The uses of duckweed. American Scientist 66 (July/August):442-451

Journey W K, Skillicorn P and Spira W 1991 Duckweed aquaculture, A new aquatic farming system for Developing countries. The World Bank Emena Technical Department, Agriculture Division.  http://www-wds.worldbank.org/servlet/WDSContentServer/WDSP/IB/1991/09/01/000009265_3961001235359/Rendered/PDF/multi_page.pdf

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Robinette H R, Brunson M W and Day E J 1980 Use of duckweed in diets of channel catfish. Proceedings. 13th Annual.Conference. SE Association. Fish Wildlife Age 108-114

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Received 30 November 2007; Accepted 18 December 2007; Published 1 January 2008

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