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Suitability of Duckweed (lemna Minor) as Feed for Fish in Polyculture System

M.Z.H. Talukdar
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M. Shahjahan
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M.S. Rahman
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

The experiment was conducted to evaluate the effects of duckweed (Lemna minor) as feed on fish production in polyculture. The experiment had 2 treatments where in treatment 1 (T₁) ponds were supplied with duckweed as feed and in treatment 2 (T₂) ponds were kept as control (without supply of duckweed). Average survival rates in T₁ and T₂ were 90 and 89%, respectively. The specific growth rates (SGR) were higher in T₁. Calculated net production in T₁ was 6.25 tons ha.^-1 yr.^-1 and in T₂ was 2.84 tons ha.^-1 yr.^-1. The ranges of physico-chemical parameters analyzed were within the productive limit and more or less similar in all the ponds under both treatments during the experimental period. There were 24 genera of phytoplankton under 5 major groups and 10 genera of zooplankton under 3 major groups found in the experimental ponds. The net production in T₁ was significantly higher than that of T₂ indicated the use of duckweed as feed for fishes is economically sustainable in polyculture.

Keywords: Duckweed, Polyculture, Fish, feed, Production, Pond, Water quality

Location: Bangladesh Agricultural University, Mymensingh, Bangladesh.

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Feed

Objectives:

To evaluate the effect of duckweed (Lemna minor) as feed on the fish production in polyculture system.

Methodology:

The experiment was conducted for a period of 90 days in the earthen ponds each measuring 1 decimal (40-m2) area at Bangladesh Agricultural University, Mymensingh, Bangladesh.Before fish stocking water of the experimental ponds were drained out to eradicate all the undesirable fishes, renovated and liming was done in all the ponds at the rate of 1 kg 40 m-2. Ponds were filled up with deep tube well water and fertilized with poultry dropping 10 kg, urea 100 g and TSP 100 g 40 m-2 as initial doses.The experiment had two treatments each with three replications. In T₁, ponds were supplied with duckweed as supplementary fish feed and in T₂, ponds were kept as control (without supply of duckweed). Ponds were stocked at a stocking density of 151 fingerlings per decimal (40-m²) at the ratio of tilapia: sharpunti: grass carp: catla: mrigal = 45: 38: 15: 38: 15.The ponds were fertilized fortnightly with poultry dropping 10 kg, urea 60 g and TSP 90 g per 40 m² to grow natural food phytoplankton and zooplankton. Fresh duckweeds were supplied everyday to the ponds (T₁) at the rate of 50% of the total body weight (wet weight basis) of the fish.Various physical and chemical water quality parameters of the ponds such as water temperature (°C), transparency (cm), dissolved oxygen (mg L^-1), pH, free CO2 (mg L^-1), total alkalinity (mg L^-1), PO4-P (mg L^-1) and NO3-N (mg L^-1) were estimated fortnightly. Water temperature was recorded with a Celsius thermometer and transparency was measured with a Secchi disc of 30 cm diameter. Dissolved oxygen was measured directly with a DO meter (Lutron, DO-5509) and a portable digital pH meter was used to measure pH. Free CO₂ and total alkalinity were determined. PO4-P (mg L^-1) and NO3-N (mgL^-1) were determined by a Hach Kit (DR/2010, a direct reading Spectrophotometer).Biological parameters of ponds water such as phytoplankton density (cells L^-1) and zooplankton density (cells L^-1) were estimated fortnightly. The counting of plankton (both phytoplankton and zooplankton) was done with the help of Sedgwick- Rafter Counting Cell (S-R cell) under a compound binocular microscope. The plankton population was determined. Identification of plankton (phytoplankton and zooplankton) up to generic level were made.Fish samples were collected with a cast net monthly to estimate the growth in length (cm) and in weight (g) and to check up the health condition of fish. At the end of the experiment, all fish were harvested through repeated netting by seine net to calculate gross and net production of fish.

Source of Information: ISSN: 2224-0616 Int. J. Agril. Res. Innov. & Tech. 2 (1): 42-46, June, 2012 Available online at http://www.ijarit.webs.com

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Suitability of duckweed as feed for fishes was analyzed in polyculture system. Most of the water quality parameters of the ponds under T₁ and T₂ were more or less similar but the higher production of fish was recorded in T₁. The reason behind the higher production in T₁ was due to supply of duckweed as feed. Influence of duckweed on production of fish is positively significant indicated that duckweed might be used as preferable feed items for fishes in polyculture.

Knowledge Management: Journal