M.M.R. Siddiquee
Department of Fisheries, Matshya Bhavan, Ramna, Dhaka - 1000, Bangladesh
M.F. Rahman
Department of Fisheries, Matshya Bhavan, Ramna, Dhaka - 1000, Bangladesh
N. Jahan
Department of Fisheries, Matshya Bhavan, Ramna, Dhaka - 1000, Bangladesh
K.C.A. Jalal
Department of Biotechnology, Kulliyah of Science, International Islamic uniersity Malaysia, Jalan Sulatn Ahmad Shah, Bandar Indera Mahkota, 25200 Kuantan, Pahang, Malaysia
S.M.N. Amin
Department of Aquaculture, Faculty of Agriculture, 43400 Serdang, Selangor, Malaysia
A. Arshad
Department of Aquaculture, Faculty of Agriculture, 43400 Serdang, Selangor, Malaysia
Indigenous carps, Exotic carps, Food electivity, Dietary overlap, Physicochemical parameters
Department of Fisheries, Matshya Bhavan, Ramna, Dhaka
Animal Health and Management
Study area and duration: The experiment was conducted in a rain fed artificial pond situated at the experimental pond area of the Department of Aquaculture, Bangladesh Agricultural University (BAU), Mymensingh for a period of nine months from April 2009 to December 2009. The size of the pond was 0.06 hectare with an average depth of 1.5 m. Pond preparation: The pond was prepared by removing the bottom mud and raising the height of embankments. After that, lime was applied at the rate of 250 kg ha-1. Before being used lime was diluted with water and then broadcasted over the bottom of the pond. After 15 days of lime application pond was filled up with water with a depth of 1.5 m. After that, 4,500 kg ha-1 cow dung, 125 kg ha-1 urea and 62.5 kg ha-1 Triple Super Phosphate (TSP) were applied in an initial dose. After diluted of urea and TSP were broadcasted throughout the pond and cow dung was applied the pond corners. Stocking the pond: After seven days of fertilization, ponds were stocked with the fingerlings of six carp species of both indigenous and exotic origin, namely rohu (Labeo rohita), catla (Catla catla), mrigal (Cirrhinus mrigala), silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis) and mirror carp (Cyprinus carpio). These fishes were stocked at the rate of 10,000 (No. ha-1) with 100 rohu, 100 catla, 100 mrigal, 100 silver carp, 100 bighead carp and 50 mirror carp. In stocking time the number, length (cm) and weight (g) of each species were recorded. All fingerlings were collected from the specific hatcheries. Transportation of fingerlings was done very carefully as much as possible in order to minimize the mortality. Before stocking the fingerlings were acclimatized for three hours. Application of fertilizers: The pond was fertilized fortnightly throughout the experimental period with cow dung, urea and TSP at the rate of 4,500, 62.5 and 31.25 kg ha-1, respectively. Cow dung was always applied at the pond corners but the urea and TSP were spread throughout the pond after diluted. Collection and preservation of planktonic samples: Ten liter samples of water were collected from different areas and depth of the pond fortnightly and filtered through a fine mesh phytoplankton net. Filtered sample was taken into a plastic vial and carefully make up to a standard volume with distilled water. With a series of settling and re-suspension procedures, plankton were concentrated into 50 mL and preserved using 5% formalin in small plastic bottles for subsequent studies. Identification and enumeration: Using a Sedgwick-Rafter cell and a binocular microscope (Olympus model-BH-2, with phase contrast facilities), 1 mL sub-sample was examined from each 50 mL preserved sample. All organisms, present in 10 cells other 5-R cell chosen at random were counted and identified up to genus level. Identification of plankton was made with the help of standard methods. Then, plankton population as cell/1 was determined. The percentage composition of each genus and family was then calculated from the raw data. Collection of fish sample: Fishes were collected by using a cast net. Fortnightly, sampling of fish was done throughout the experimental period. Sample of five fish from each species except mirror carp was collected at each sampling date. Only three mirror carp was sampled due to its small stocking number. All fishes were killed immediately by a blow on the head. Fishes were then preserved in a jar containing buffered 10% formalin to prevent further digestion of food item in the stomachs of the fish. Then, the jars with fish were taken back to the laboratory for further analysis. Stomach contents analysis: The abdomen of the individual fish was cut open and the gut contents were taken out carefully and then put into a clean petri dish. Only the anterior portion of the digestive tract lying between the esophagus and the small intestine has been used for the present study. This has been done because the food items in this portion of the digestive tract are least digested and mostly identifiable. The stomach content of individual fish has removed into a clean petri dish with the help of a fine needle. Then, it was diluted with distilled water to 20 mL. One milliliter sub-sample from 20 mL sample was transferred by a pipette to a Sedgwick-Rafter cell. Using a binocular microscope, all organisms found in 10 of the thousand cells chosen at random, were identified and counted. All the organisms were identified up to genus level. Electivity indices: The electivity indices were determined by applying Ivlev (1961) formula as follows:
where, ri is the relative content of any ingredient in the ration expressed as percentage of total ration and pi is the relative proportion of same item in the environment. The calculated value of E ranges from+1 to -1, where positive values indicate selection for certain food items, negative values indicate avoidance.
Dietary overlap: Dietary overlap were measured by using Schoener’s index :
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a = 1-0.5 (n = 1pxi-pyi1)
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where, a is the overlap index, pxi is the proportion of food category in the diet of species x, pyi is the proportion food category in the diet of species y and n is the number of categories.
Pakistan Journal of Biological Sciences, 15: 568-575; ISSN 1028-8880
Journal