et al., 1996). Currently, approximately 80% of the animal protein supply for residents is provided by fish, but population growth is rapidly overwhelming the productive potential of the Bangladesh fishery (OÕRiordan, 1992). Since the 1960s, per capita availability of fish has dropped from 12 kg to only 7 kg; moreover, among lower income groups per capita consumption is only 4.4 kg. For the poorest of the poor, fish is simply unaffordable (OÕRiordan, 1992). Thus, increasing aquaculture production plays an important role in meeting the nutritional needs of Bangladesh people.
Bangladesh has a variety of aquaculture and fisheries projects that have been funded by international aid. Many nongovernmental organizations (NGOs) such as PROSHIKA, Bangladesh Rural Advancement Committee (BRAC), and Caritas have been promoting aquaculture development independently through their own extension networks in Bangladesh.
Aquaculture is commonly practiced using polyculture of four to seven species of Indian and Chinese carps in manured and/or fertilized ponds (Wahab et al., 1991). Despite extensive research conducted on fertilization of carp polyculture ponds in many parts of the world, such information in Bangladesh is rather scarce (Haq et al., 1993). Fish production is quite low in Bangladesh, averaging 2,800 kg ha-1 yr-1 (DOF, 1999). In rural aquaculture ponds, fish production is often lower than 1,500 kg ha-1 yr-1. NGOs have been working with farmers to increase fish production; however, different NGOs recommend different fertilization regimes to farmers, and these regimes do not all seem to increase yields. Fertilization regimes should vary with different local conditions such as soil and source water. In some cases the same farmers receive very different recommendations on fertilization regimes from different extension partners. Both over- and under-fertilization may cause adverse effects on fish production, water quality, pond effluents, and economic returns. It is necessary to evaluate fertilization regimes and recommend appropriate fertilization strategies to farmers in order to maximize fish production,
maintain good water quality, reduce environmental impact, and maximize economic returns.
An on-station trial was conducted in carp polyculture ponds at the Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh during July to December 2001 (See 10ATR4A, ÒOn-Station Trial of Different Fertilization Regimes Used in BangladeshÓ). This trial was designed to evaluate five fertilization regimes and to compare effects of different fertilization regimes on fish production, water quality, and economic returns. The tested fertilization regimes for the on-station trial were:
A) PROSHIKA fertilization regime: weekly application of
1,000 kg cow dung ha-1; B) BRAC fertilization regime: weekly application of 156 kg cow dung ha-1, 28.125 kg urea ha-1, and 13.1 kg TSP ha-1; C) Caritas fertilization regime: fortnightly application of 1,500 kg cow dung ha-1; D) BAU fertilization regime: fortnightly application of 1,250 kg cow dung ha-1,
31.25 kg urea ha-1, and 15.625 kg TSP ha-1; and E) CRSP fertilization regime developed for Nile tilapia (Oreochromis niloticus) ponds: weekly application of 250 kg cow dung (dry matter) ha-1 supplemented with urea and TSP to give 28 kg N and 7 kg P ha-1 wk-1. Among all tested fertilization regimes, the CRSP fertilization regime resulted in the highest fish production, followed by BAU, BRAC, Caritas, and PROSHIKA fertilization regimes (P < 0.05). Two fertilization regimes (PROSHIKA and Caritas) using cow dung as the sole nutrient input during the culture period gave very poor fish growth performance and low production, due mainly to the low soluble nutrients derived from cow dung. The other three fertilization regimes (CRSP, BAU, and BRAC) using combinations of organic and inorganic fertilizers resulted in much higher carp production. Analysis of water quality showed that nutrients were oversupplied in the CRSP fertilization regime because this regime was developed in Nile tilapia monoculture with higher intensification compared to carp polyculture. The BAU fertilization
