INTRODUCTION

In Bangladesh, there are about 1.5 million ponds of different sizes covering an area of about 146,955 hectares of land of which about 52% 1s under extensive fish culture (DoF 1991). Although, fish culture in ponds 1s not a new practice in the country, the rate of production of fish 1s still lying far below (1161 kg/ha/yr) than what 1t should be (Rahman 1989). Improper management and production techniques viz. high or low stocking, inadequate manuring and feeding etc. have been considered responsible for low production of fish.

As most of the farmers are poor and living in rural area, 1t 1s not possible for them to support the intensive technology of fish production which requires higher inputs supply. An appropriate intermediate technology for the farmers of Bangladesh, thus should be the semi-intensive culture technique that require moderate inputs and production management based mainly on proper stocking rate and ratio and adequate regular manuring with or without supplementary feeding.

Production of fish through semi-intensive polyculture or integrated fish farming by using animal or agricultural by-products in fish pond as manure and feed has appeared to be the most appropriate technique for rural farmers.

Scope of using cow dung in fish pond 1s limited in Bangladesh because of increased application of cow dung as fuel and as manure in crop lands. Chicken manure which 1s rich in nutrients 1s not yet properly utilized in the country.

In Noakhali area, production of fish through semi-intensive polyculture was observed to range from 2470 – 3700 kg/ha/yr (Ammen 1987). Several trails were conducted on integrated fish-cum-poultry farming system at Fisheries Research Institute (FRI), Mymensingh and a production of around 4500 kg/ha/yr of fish have been achieved (FRI, 1991).

The FAO/UNDP Project BGD/87/045 demonstrated the techniques of increasing fish production through semi-intensive polyculture and integrated fish-poultry farming at government farms. The objective of the trails was to standardize the generally applicable fish production techniques which the local fish farmers could adopt and practice by themselves.

MATERIALS AND METHODS

POLYCULTURE

Selection of ponds:

Two ponds were selected for demonstrating technique of polyculture of fish taking one pond at Faridpur FTEC and the other at Tongi FSMF. Two successive trials were done in the same pond at Faridpur FTEC in 1990 – 91 and in 1991 – 92. The ponds were perennial and retained an average water depth of about 3.0 m at Faridpur and 2.5 m at Tongi.

Pond preparation:

The ponds were dewatered by low-lift pumps prior to stocking with fish fingerlings in order to eradicate the unwanted fishes. After dewatering, the pond bottoms were exposed to sunlight for 3–4 days and then treated with lime @ 250 – 300 kg/ha. Base manuring was done with poultry drops/cow dung @1,500 – 2,000 kg/ha. The manure was spread evenly all over the pond bottom. Immediately after manuring, the ponds were gradually filled in with water from adjacent ponds and/or from tube-well over a period of about 5–7 days.

Stocking:

The ponds were stocked with fish fingerlings after 5–7 days of base manuring when production of natural fish food organisms in sufficient quantity was observed in pond water. The objective of the first trial at Faridpur FTEC pond was to raise brood fish for the hatchery hence large size fish were stocked for that trail only.

Considering the diversified pond ecosystem, species of fishes were selected carefully ensuring maximum utilization of different trophic and spatial niches of ponds which are not competitive to each other for food and space. List of compatible stocked fish species 1s given in Table-I.

TABLE I: SELECTED SPECIES OF CARPS AND THEIR SPATIO-TROPHIC HABITS

Stocking density varied from 7660 – 12473 fingerlings/ha. Fingerlings were collected from both the DOF Fish Seed Multiplication Farms (FSMF) and private fish nurseries. Average weight of stocked fish/fingerlings varied from 0.5 – 3500 g. Pond-wise stocking details are given in Table II.

TABLE II: STOCKING DETAILS OF DEMONSTRATION PONDS FOR POLYCULTURE

Manuring:

The ponds were regularly manured with poultry drops/cow dung @ 50 – 80 kg/ha/day in between 9 – 11'0 clock in the morning. The manure was spread over the water from all sides of the ponds. Inorganic fertilizer (Urea and TSP) was applied in small quantity from time to time.

Feeding:

Supplementary feed was applied in all the three trials with mustard oil cake (50%) and rice bran (50%) or wheat bran (50%) @ 1 – 2% body weight of fish except plakton feeding silver carp, catla and macrophyte feeding grass carp. Green grass and/or duck weed was also applied in ponds for grass carp.

Harvesting and marketing:

Large size fish (around 500 g) were partially harvested after 3/4 months of stocking. The ponds were again re-stocked with fingerlings of same species in almost same numbers. The first trial at Faridpur FTEC pond was completed in six months hence all the fish were harvested in six months time. The second trial at the same pond at Faridpur was continued for one year. The pond at Tongi was harvested in ten months culture period. A portion of harvested fish was restocked in other ponds of the farms for induced spawning and the rest was sold to local markets.