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Effects of Intervention in the Water Column And/or Pond Bottom Through Species Composition on Polycultures of Large Carps and Small Indigenous Species

A. Milstein
Fish and Aquaculture Research Station Dor, M. P. Hof Ha Carmel, 30820, Israel.

M. A. Wahab
Dept. of Fisheries Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

A. Kadir
Dept. of Fisheries Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

M. F. H. Sagor
Dept. of Fisheries Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

M. A. Islam
Dept. of Fisheries Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

Abstract/ Executive Summary:

In Bangladesh, a sustainable semi-intensive pond aquaculture technology including large carp species as cash-crop and small indigenous fish species (SIS) as food for the farmers' families is being optimized. The present paper is on the effects on fish performance and pond ecology of interfering in the water column and/or on the bottom through changes in the polyculture composition. The Control polyculture was the 'no-effect' combination consisting of the traditional 33 rohu - 33 catla - 34 common carp stocking with the addition of 250 SIS and 3 silver carp per 100 m² of pond, as resulted from a previous experiment. Interferences on the water column were achieved by changing the density of the herbivorous fish (reducing the density of catla to 24/100 m² and increasing that of silver carp to 12/100 m² ), and on the bottom by doing so on the benthophagous fish (replacing 10/100 m² common carp by the same amount of mrigal). Mola was the SIS included in the polyculture. Interfering in the water column and/or in the pond bottom through the polyculture composition produced complex responses in the pond ecosystem affecting the large carps' performances, while it did not Significantly affect the reproduction and the harvested biomass of the small fish rnola. Relationships among the different fish species and the environment are described for each polyculture. The four polycultures tested allowed a good production of large carp species as cash-crop, of silver carp as an option to consume or to sell, and of the small species mola as food for the farmers' families. The Control polyculture is appropriate to produce relatively large herbivorous species, mainly silver carp. The polyculture combination in the Water treatment is appropriate to obtain a larger amount of smaller silver carp that can be afforded by the poor people but also smaller rohu and catla, while maintaining the same level of total yield and income with reduced feed conversion ratio (FCR) than in the Control treatment. The polyculture combination in The Bottom treatment allowed a larger fish species diversity and also produced smaller herbivorous fish with still reduced FCR, while maintaining the same level of total yield and income than the Control treatment. The polyculture combination in the Water&Bottom treatment gave the best results: it allowed a larger fish species diversity, is appropriate to obtain a larger amount of small silver carp that can be afforded by the poor people, and gives the highest total yield and income with the lowest FCR.

Keywords: Fish interactions, Natural food web, Polyculture, SIS small indigenous species

Location: Fisheries Field Laboratory, Bangladesh Agricultural University (BAU), Mymensingh

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Fish

Objectives:

To effects on fish performance and pond ecology of intervention in the water column and/or on the pond bottom through changes in the polyculture composition.

Methodology:

The experiment was conducted in twelve 140-160 m² ponds of 1.5 m deep at the Fisheries Field Laboratory, Bangladesh Agricultural University (BAU), Mymensingh, involving 4 treatments, 3 replicates per treatment. The Control polyculture consisted of the traditional stocking of 33 rohu -33 catla - 34 common carp per 100 m², with the addition of 250 SIS and 3 silver carp per 100 m², which in the previous experiment was found to be a ‘no-effect’ combination in relation to the traditional stocking combination. Intervention in the water column (Water treatment) was achieved by changing the density of the herbivorous fish (reducing the density of catla to 24/100 m² and increasing that of silver carp to 12/100 m²), and on the bottom (Bottom treatment) by doing so on the benthophagous fish (replacing 10/100 m² common carp by mrigal). In the Water & Bottom treatment both interventions were carried out. The SIS stocked was mola, which has been found to be very rich in nutrients and vitamin A. Before starting the experiments ponds were drained to eradicate all predatory fishes, embankments and slopes were repaired, and agricultural lime (CaCO₃) at 2.5 kg/100 m² was applied. Ponds were filled up, and fresh cow manure (6.5 kg/100 m²) was applied in the four corners of each pond to promote algal growth. Fish were stocked on 19-May-07 and cultured for 155 days. At stocking the average weight of rohu and of catla was 40 g, mrigal and silver carp 33 g, common carp 12 g, and the SIS mola was 1.5 g. Fingerlings of the large carps were purchased from the local retailer, who collected them from rural nurseries that obtained the fertilized eggs from the nearby Government hatchery. Fingerlings of mola were collected from perennial ponds of the farmers, where farmers keep them together with major carps and where the small fish naturally breed. Inorganic fertilization was performed at 15-day intervals with urea and tri-super-phosphate at 250 g/100 m² each. Analyzes were performed at the Water Quality and Pond Dynamics Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh. Water quality data were analyzed through multivariate and univariate statistical methods. Factor analysis was used to identify ecological processes responsible for the variability of the water quality parameters measured. Split - plot ANOVA using treatment as main factor and month as sub-factor was applied to each water quality parameter and to the factors extracted. Fish data were analyzed through ANOVA to test the effect of the different treatments on the performance of each fish species. Differences between treatment (and month) levels were tested with the Duncan multi comparison test of means, using a significance level of P b 0.05. Survival (percentage) data were normalized using the arcsine of the square root transformation. Feed conversion ratios were transformed to ranks (non-parametric technique appropriate for ratios) before performing further analyzes. The analyzes were run using the SAS statistical package.

Source of Information: Aquaculture 286 (2009) 246– 253

Article Link (Online Journal): doi:10.1016/j.aquaculture.2008.09.036

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In conclusion, the Control polyculture is appropriate to produce relatively large herbivorous species, mainly silver carp. The polyculture combination in the Water treatment is appropriate to obtain a larger amount of smaller silver carp that can be afforded by the poor people but also smaller rohu and catla, while maintaining the same level of total yield and income with reduced FCR than in the Control treatment. The polyculture combination in the Bottom treatment allowed a larger fish species diversity and also produced smaller herbivorous fish with still reduced FCR, while maintaining the same level of total yield and income than the Control treatment. The polyculture combination in the Water & Bottom treatment gave the best results: it allowed a larger fish species diversity, is appropriate to obtain a larger amount of small silver carp that can be afforded by the poor people, and gives the highest total yield and income with the lowest FCR.

Knowledge Management: Journal