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Effects of Addition of Tilapia and Periphyton Substrates on Water Quality and Abundance of Plankton in Freshwater Prawn Culture Ponds

M. E. Ahsan
Department of Marine Fisheries and Oceanography, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh.

M. R. Sharker
Department of Fisheries Biology and Genetics, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh.

M. A. Alam
Department of Fisheries Biology and Genetics, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh.

M. A. B. Siddik
Department of Fisheries Biology and Genetics, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh.

A. Nahar
Department of Marine Fisheries and Oceanography, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh.

Abstract/ Executive Summary:

The research investigated the effects of addition of tilapia and periphyton substrates on water quality and abundance of plankton in freshwater prawn culture ponds. The absence and presence (0 and 0.5 individual/m²) of tilapia were investigated in 40 m² ponds stocked with 3 prawn juveniles (5.023 ±0.04g)/m² with or without added substrates for periphyton development. A locally formulated and prepared pellet feed (2mm) containing 30% protein with C/N ratio close to 10 was used. The feed was applied at the rate of the 10% body weight and gradually decreased to 3% at the end of the culture period. Water quality parameters and the abundance of plankton and periphyton biomass were measured. The abundance of plankton and periphyton biomass was significantly higher in tilapia-free ponds comparing to tilapia added ponds. The addition of substrates did not influence size at harvest but improved the survival of prawn from 54.4 to 76.9%. Substrates contributed an increase in gross and net yield of prawn by 33% and 42.5%, respectively. Addition of tilapia and periphyton substrates benefited the freshwater prawn culture through reducing toxic inorganic nitrogenous compounds in water, enhancing the utilization of natural foods and improving survival, production and economic benefit.

Keywords: Freshwater prawn, Periphyton, Plankton, Tilapia, Water quality parameter

Location: Fisheries Field Laboratory Complex, Bangladesh Agricultural University, Mymensingh.

Start Date: 20-02-2008

End Date: 20-06-2008

Program Area: Animal Health and Management

Commodity: Prawn

Objectives:

To investigate the effect of tilapia addition on prawn survival and production, pond ecology, and economic performance in presence and absence of substrates for periphyton development in freshwater prawn culture ponds.

Methodology:

The experiment was carried out for a period of 120 days from 20th February to 20th June, 2008 at the Fisheries Field Laboratory Complex, Bangladesh Agricultural University, Mymensingh. A pond (81m×8.9m) was drained completely and portioned by galvanized iron sheets into 18 small ponds (40m² each) of which 12 ponds were used for this experiment. An on-station trial was conducted with a 2×2 factorial design with the absence or presence (0 or 0.5 individual/m²) of tilapia in monoculture of freshwater prawn (3 juveniles/m²) as first factor, and with and without substrates addition for periphyton development as second factor. The treatments without periphyton substrates are referred to as ‘T₀P₀’ and ‘T_0.5P₀’, while the treatments with periphyton substrates are referred to as ‘T₀P’and ‘T₀.5P’. Pond Preparation and Stocking: Before beginning the experiment, ponds were renovated and cleaned of aquatic vegetation. Quicklime (CaO) was applied to the pond bottom at the rate of 250kg/ha. All ponds were fertilized with semi-decomposed cattle manure, urea and triple super phosphate (TSP) at the rates of 3000, 100 and 100kg/ha, respectively. The shelter was built by bamboo kanchi with date tree leaves. About 436 bamboo branches (locally known as kanchi) with a mean diameter of 0.05m were kept vertically into the bottom mud of each pond, excluding a one meter wide perimeter water surface from the dike. Bamboo branches increased an additional area for periphyton development equivalent to about 60% (i.e. 24m²) of the pond surface area. The ponds were stocked with large size juveniles of prawn and tilapia having average weight of 5±0.4g and 24.3±0.24g respectively. A locally formulated and prepared pellet feed (2mm) containing 30% protein with C/N ratio close to 10 was used. The feed was applied initially at the rate of 10% body weight and gradually decreased to 3% of the body weight. The prawn and tilapia were sampled using a cast net to adjust the feeding rate. Water quality monitoring: Water quality parameters such as temperature (°C), dissolved oxygen (mg/l), transparency (cm), were measured weekly, total alkalinity ((mg/l), phosphate-phosphorus (mg/l), nitrate-nitrogen(mg/l), nitrite-nitrogen (mg/l), ammonia-nitrogen (mg/l) and chlorophyll-a (mg/l) were measured monthly. Water temperature was recorded in the field with the help of a celsius thermometer. The transparency of water was measured by a Secchi disc of 20 cm diameter. pH of pond water was determined by a direct reading digital pH meter in the laboratory. The dissolved oxygen was measured by using a portable digital DO meter. Ammonia-nitrogen (TAN), Nitrate-nitrogen (NO₂-N), Nitrite-nitrogen (NO₃-N), Phosphate-phosphorous (PO₄-P) were determined by using HACH Kit. Chlorophyll-a was measured using filter papers and spectrophotometer at 664 and 750 nm wave lengths. The analyses of water quality parameters were done in the Water Quality and Pond Dynamics Laboratory, Dept. of Fisheries Management, BAU, Mymensingh. Collection of plankton sample and preservation: Plankton samples were collected fortnightly from each pond. Ten liters of water sample was taken from different places and depths of the pond and passed through fine (25μ) mesh plankton net. Filtered samples were taken into a measuring cylinder and carefully made up to a standard volume of 50ml. Then the collected plankton samples were preserved in 5% buffered formalin in small plastic bottles for subsequent studies. Qualitative and quantitative study of plankton: From each 50 ml preserved sample, 1 ml sub-sample was examined using a Sedge Wick-Rafter Cell (S-R Cell) and a binocular microscope (Olympus CH-40). One ml sub sample from each sample was transferred to the cell and then all planktonic organisms present in 10 squares of the cells chosen randomly were identified and counted. The quantitative estimation of plankton was done. Growth Sampling of Prawn: Monthly sampling was done by using a cast net to observe the growth of prawn and to adjust the feeding rate. Growth of prawn in each sampling was measured by using a digital electronic balance. Analysis of experimental growth data: Experimental data collected during the growth trial were used to determine. After 120 days culture, adult freshwater prawn were harvested and counted for total number separately from each pond to evaluate the survival rate. After direct counting, weight and length of each individual prawn juvenile was also taken. Analysis of the data was done by using the software SPSS version 11.5 significance was assigned at 5% level.

Source of Information: INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 3, ISSUE 2, 272-278, FEBRUARY 2014

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Addition of tilapia and periphyton substrates benefited the freshwater prawn culture through reducing toxic inorganic nitrogenous compounds in water, enhancing the utilization of natural foods and improving survival, production and economic benefit.

Knowledge Management: Journal