Bacterial flora of fish feeds and organic fertilizers for fish culture ponds in Ghana

Abstract

Use of animal manure to fertilize fishponds has been reported in many parts of the world (Bardach, Ryther & McLarney 1972; Woynarovich 1979; Hopkins, Cruz, Hopkins & Chong 1980; Oladosu & Ayinla 1992; Ayinla, Oladosu, Ajiboye & Ansa 1994; Njoku 1997). In Ghana, poultry manure, cow manure, pig manure and cow blood from abattoirs are mostly used to fertilize fishponds. Some farmers make periodic applications at 3‐ or 4‐month intervals. Others depend on visual observation and add the fertilizer according to the colour of the pond water. Others do it once in the production cycle of the pond.

The use of animal wastes to fertilize pond farms as practised in many countries is considered superior to inorganic fertilizers in producing and maintaining desirable species of planktonic and benthic organisms (Pillay 1992) and to enhance fish production (Edwards 1980; Yadava & Garg 1992; Garg 1996; Garg & Bhatnagar 1996). As manuring causes organic enrichment, it may also hasten the deterioration of the water quality making the aquatic environment favourable for the growth and multiplication of human pathogenic bacteria (Garg & Bhatnagar 1996). Pathogenic bacteria such as Aeromonas, Citrobacter, Edwardsiella, Enterobacter, Escherichia coli, Klebsiella and Serratia may be introduced into the aquatic environment (Cuelin 1962; Rao, Parhad, Rao & Rao 1968; Cohen & Shuval 1973; Evison & James 1973; Allen, Austin & Colwell 1983; Austin & Austin 1993; Ringo, Strom & Tabachak 1995).

Food is one of the chief vehicles of gastrointestinal disease, and limits have therefore been established for the numbers of pertinent categories of microorganisms tolerable in various foods (Statutory Orders and Regulations 1955; Thatcher & Clark 1968; Powers, Ay & Rowley 1970).

Fish farming in Ghana has been more on the subsistence level and most farmers do not use commercial feeds. They mostly depend on household waste and other agricultural byproducts of low price. To them, any item that sustains the fish is food. This communication is intended to make workers of fishponds using these feedstuffs and fertilizers aware of the microbial burden of the inputs used in fish farming in Ghana.