Growth of red tilapia (Oreochomis mossambicus) and black tilapia (Oreochomis niloticus) with common carp (Ciprinus carpio) in monoculture and polyculture by using natural feed in ponds fertilized with biodigester effluent

Nguyen Huu Yen Nhi and T R Preston*

An Giang University, 25 Vo Thi Sau St., Long Xuyen City, Vietnam
nhynhi@agu.edu.vn
* TOSOLY, AA 48 Socorro, Colombia.

Abstract

This experiment was carried out in the research farm of An Giang University from November 2011 to February  2012 to compare growth of red tilapia (Oreochomis mossambicus) and black tilapia (Oreochomis niloticus) in monoculture and polyculture with Common carp (Ciprinus carpio) in an outdoor natural pond system, using biodigester effluent as fertilizer and duckweed as feed supplement. There were four treatments arranged as a 2*2 factorial with three replicates in a completely randomized design. The factors were: Red (RT) or Black (BT) tilapia in monoculture or polyculture with Common carp (C). Fish density was 5 fish/m² with proportions of tilapia: Common carp of 5:1 in the polyculture treatments. The pond size was 4m².   Biodigester effluent was applied daily at the rate of 0.484g N per pond per day. The ponds were seeded with duckweed to cover approximately 70% of the pond surface.

The growth rates in weight and length of the black tilapia were higher than for red tilapia, both in monoculture and in polyculture with Common carp. There were no advantages in net fish yield of combining tilapia with Common carp. The net fish yield with black tilapia was 7 tonnes/ha in 90 days, equivalent to an annual yield of 30 tonnes/ha.

Key words: Duckweed, feed supplement, recycling

Introduction

Fish production makes an important contribution to global food supply. It is also necessary to cope with the considerable and increasing demand for new feeds for fish by using natural sources, especially in response to climate change and depletion of non-renewable resources.

The human population is increasing in developing countries so the animal production demand also increases. This leads to increases in water pollution caused by discharging of waste feed and excreta, especially in intensive aquaculture. This is already a problem in the rural areas of Mekong Delta eat (Tran Thi Phan and Takeshi Watanabe 2002). There are many methods to resolve this problem, one of which is the use of the biodigester system. The products from the biodigester are gas for cooking and effluent that can be used as fertilizer for vegetables like water spinach (Kean Sophea and Preston 2001; Ly Thi Luyen 2003; Ho Bunyeth 2003), in fish ponds (San Thy et al 2004; Sen Sorphea et al 2010;  Tick and Preston 2012) or for water plants like duckweed (Le Ha Chau 1998). Biodigester effluent was reported to contain up to 1004 mg N/litre of which 40% was ammonia-N (Bui Phan Thu Hang 2003).

Duckweed (Lemna spp.) is rich in nutrients. It has been used as a main protein supplement for pigs (Bui Hong Van et al 1997), ducks (Bui Xuan Men et al 1995; Nguyen Duc Anh et al 1997) and fish (San Thy et al 2004; Latsamy and Preston 2007; Sen Sorphea et al 2010;  Tick and Preston 2012) and also as a source of minerals for ruminants (Leng et al 1995). Duckweed has the capacity to grow rapidly on nutrient-rich waste water and produce biomass rich in protein (Leng et al 1995).

Aquaculture systems are mostly practiced in cage or pond  culture, and fish may be raised in mono- or poly-culture.  However, to optimize the use of natural resources, the integration of animals, crops and fish is recommended (Preston 2009).  In this context it is considered that the application of biodigester effluent in fish ponds could be a way of increasing feed availability for fish through growing of duckweed, phytoplankton and zooplankton,  and at the same time reducing problems of pollution to the environment.

Hypotheses

• Net fish yield from natural ponds seeded with duckweed will be increased by raising Tilapia and Common carp in poly-culture compared with Tilapia in monoculture. 

• The Red and Black Tilapia will respond differently in growth rate when raised in natural ponds seeded with duckweed.

Materials and methods

Location and climate 

This experiment was conducted in the farm of An Giang University, Long Xuyen City, Vietnam. The climate is tropical monsoon, with a rainy season between May and October and a dry season from November to April. The mean air temperature is 27°C and annual rainfall 1400-1500 mm. The duration of the study was 90 days, from December 2011 to March 2012. 

Experimental treatments and design  

The experiment was conducted in a completed randomized design (CRD) with 4 treatments arranged as a 2*2 factorial with 3 replicates. The factors were fish species (Red versus Black tilapia) and culture system (Tilapia in monoculture or in polyculture with Common carp). The individual treatments were: 

• BT: Black tilapia only 
• BTC: Black tilapia: Common carp (5:1) 
•  RT: Red tilapia only 
• RTC: Red tilapia : Common carp (5:1)

Fingerlings  

The fingerlings of Black tilapia, Red tilapia and Common carp were bought from the hatchery in Long Xuyen City with an initial weight of  7.43 – 7.50 g/fish.

Management

Twelve earthen ponds (2m deep x 2m wide x 2m long) (Photo 1) were lined with plastic sheet to avoid filtration of the water.  Biodigester effluent was taken from a plug-flow tubular plastic biodigester charged with pig manure, and applied to the ponds in quantities equivalent to  0.484g N/day. The ponds were seeded with duckweed  in amounts that covered an area of about 70% of the pond surface. The tilapia and Common carp were introduced into the ponds at the rate of 5 fish/m². One third of the water in the ponds was changed daily.

Photo 1. The pond system

Measurements 

The temperature,  pH and transparency of the water and the concentrations of dissolved oxygen  (DO), nitrite (NO₂^-) and total ammonia nitrogen (TAN) were measured every two weeks.  The weight and length of fish, and the densities of phytoplankton and zooplankton, were measured at the beginning of the experiment, and then at monthly intervals.

Specific growth rate (SGR) was calculated as 
SGR (%/day) = 100 [Ln(w_f) – Ln(w_i)]/T ….(i) 

where:                

   W_f: Final weight (g) 

    W_i: Initial weight (g) 

     T: Number of days 

Daily weight gain (DWG) was calculated as: 

DWG (g/day) = (w_f - w_i)/T ……………….(ii)

Survival rate (SR%) was calculated as: 

SR (%) = 100[number of fish harvested/initial number of fish] …….(iii) 

The densities of phytoplankton and zooplankton were measured according to the method of Coutteu (1996).

Density of phytoplankton (cells/ml) and zooplankton (individuals/ml) were counted in a Sedgwick-Rafter counting chamber according to the formula:

Density = (T x1000 xV_cd)/(A x N x V_mt)

In which:

T: Total number of cells/individuals counted

A: area of ​​ the cell count

N: number of cells counted

V_cd: the volume of water condensed

V_mt: the volume of sample collected

Chemical analysis 

Samples of duckweed were analyzed for DM, nitrogen (N), ether extract, and organic matter (OM) according to the procedures of AOAC (1990).
 

Statistical analysis 

The data were analyzed using the General Linear Model (GLM) of the ANOVA program in the  Minitab software (Minitab 2000). Sources of variation were: fish species, culture system, interaction culture system* fish species and error.

Results and discussion

Water quality 

The parameters of water quality were similar for all treatments (Table 1) and were within the accepted range for the normal growth of fish (Boyd 1990). The densities of both phytoplankton and zooplankton increased linearly during the experiment (Figures 1 and 2). There were no differences between the ponds with the different species of Tilapia nor  between ponds having mono- or poly-culture systems. The steady growth in both phytoplankton and zooplankton presumably was the result of regular application of biodigester effluent to the ponds.

Figure 1. Trends in the density of phytoplankton during the experiment	Figure 2. Trends in the density of zooplankton during the experiment

Chemical composition of duckweed  

The average protein level of the duckweed during the experiment (Table 2)  was similar to that reported by Tu et al (2012) for duckweed fertilized with biodigester effluent at 150 kg N/ha. In the present experiment the N application from the biodigester effluent was 109 kg applied over the 90 days of the experiment.

The effluent contained 876 mg N/liter which was only slightly lower than the 900 mg/liter, eported in an earlier experiment (Yen Nhi and Preston 2011). This probably reflected differences in the feed received by the pigs and the concentration of solids in the influent to the biodigester.

After 15 days duckweed was supplied to each pond as the area was insufficient to support the amount of duckweed biomass consumed by the fish.  The total weight of duckweed supplied for each pond ranged from 33.8  to 34.9 kg. There were no differences among treatments  (Table 3).

 Growth performance  

 The black tilapia grew 25% faster than the red tilapia in mono-culture and 22% faster when in poly-culture with Common carp (Tables 4 and 5).  Changes in specific growth rate and growth in length showed a similar pattern. Survival rates were high and not affected by species of Tilapia nor the culture system.

Figure 3. Weight gain of black (BT) and red (RT) tilapia, black tilapia with common carp (BTC) and red tilapia with common carp (RTC)

 Changes in weight: length ratio

 Both species of tilapia showed an increase in the weight: length ratio as the experiment progressed (Table 7). After 90 days the weight: length ratio of black tilapia was higher than that of the red tilapia. ; however, the differences between treatments were insignificant (p>0.05), except at 30 days. 

 Economic analysis 

The net fish yield was higher for the treatments with black tilapia and was not affected by the presence or absence of the Common carp (Table 8; Figure 4). On an annual basis, assuming similar growth rates, the yield would be close to 30 tonnes/ha for the treatments with black tilapia. This is considerably higher, than was reported for natural ponds supplemented with duckweed, by San Thy et al (2004) (9 tonnes/ha), Sen Sorphea et al (2010) (7 tonnes/ha), Tick and Preston (2012) ( 10 tonnes/ha) and Journey et al (1991) (10 tonnes/ha).

Figure 4. Net fish yield of black (BT) and red (RT) tilapia, black tilapia with common carp (BTC) and red tilapia with common carp (RTC)

Conclusions

• The growth rates in weight and length of the black tilapia were higher than for red tilapia, both in mono- and poly-culture with Common carp.
  
  
• There were no advantages in net fish yield of combining tilapia with Common carp
  
  

• The net fish yield with black tilapia was 7 tonnes/ha in 90 days, which represents a potential annual yield of 30 tonnes/ha.

References

AOAC 1990 Official methods of analysis. Association of Official Analytical Chemists, Arlington, Virginia, 15^th edition, 1298 p

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.

Bui Hong Van, Le thi Men, Vo van Son and Preston T R 1997 Duckweed (Lemna spp) as protein supplement in an ensiled cassava root diet for fattening pigs.  Livestock Research for Rural Development 7 (3) http://www.lrrd.org/lrrd9/1lemen911.htm

Bui Phan Thu Hang 2003 Effect of dimensions of plastic biodigester (width:length ratio) on gas production and composition of effluent. http://mekarn.org/msc2003-05/miniprojects/webpage/hangctu.htm 

Bui Xuan Men, Ogle R B and Preston T R 1995 Use of duckweed (Lemna spp) as replacement for soya bean meal in a basal diet of broken rice for fattening ducks. Livestock Research for Rural Development 7 (3) http://www.lrrd.org/lrrd7/3/kean136.htm
 

Coutteau  P 1996  Micro-algae.  In:  Manual  on  the  production  and  use  of  live  food  for aquaculture. Patrick Lavens and Patrick Sorgeloos (Editors). Published by Food and Agriculture Organization of the United Nations: 9-59. 

Ho Bunyeth  2003 Biodigester effluent as fertilizer for water spinach established from seed or from cuttings;  Retrieved , from MEKARN Mini-projects. http://www.mekarn.org/MSc 2003-05/miniprojects/web page/buny.htm

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

Kean Sophea and Preston T R 2001 Comparison of biodigester effluent and urea as fertilizer for water spinach vegetable.  Livestock Research for Rural Development 13 (6) http://www.lrrd.org/lrrd13/6/kean136.htm

Latsamy P and Preston T R 2008 Fly larvae, earthworms and duckweed as feeds for frogs in an integrated farming system. Livestock Research for Rural Development. Volume 20, supplement. http://www.lrrd.org/lrrd20/supplement/lats2.htm

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

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Ly Thi Luyen 2003 Effect of the urea level on biomass production of water spinach (Ipomoea aquatica) grown in soil and in water;  Retrieved , from MEKARN Mini-projects. http://www.mekarn.org/MSc 2003-05/miniprojects/web page/luyen.htm

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

Nguyen Duc Anh and Preston T R 1997. Evaluation of protein quality in duckweed (Lemna spp.) using a duckling growth assay.  Livestock Research for Rural Development.  http://www.lrrd.org/lrrd9/2/anh92.htm

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Sen Sorphea, Lundh T, Preston T R and Khieu Borin 2010 Effect of stocking densities and feed supplements on the growth performance of tilapia (Oreochromis spp.) raised in ponds and in the paddy field   MSc Thesis, MEKARN-SLU http://www.mekarn.org/MSC2008-10/theses/sorp_1.htm

Tick N and Preston T R 2012 Effect of biodigester effluent, duckweed and leaves from Taro (Colocacia esculenta) on growth of Tilapia (Oreochromis niloticus) in open ponds. Livestock Research for Rural Development. Volume 24, Article #25. http://www.lrrd.org/lrrd24/2/tick24025.htm 

Tran Thi Phan and Takeshi Watanabe 2002 Development of the new technologies and their practice for sustainable farming systems in the Mekong Delta. Proceeding of the 2002 Annual Workshop of JICAS Mekong Delta Project. November 26-28, 2002. College of Agriculture, CanthoUniversity. Vietnam

Tu D T M, Dong N T K and Preston T R 2012 Effect on composition of duckweed (Lemna minor) of different levels of biodigester effluent in the growth medium and of transferring nutrient-rich duckweed to nutrient-free water. Livestock Research for Rural Development. Volume 24, Article #71. http://www.lrrd.org/lrrd24/4/mytu24071.htm

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. Retrieved May 27, 2012, from http://www.lrrd.org/lrrd23/7/nhi23161.htm

Received 29 March 2012; Accepted 26 June 2012; Published 1 July 2012

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