Effects of compost manure on the bioaccumulation and toxicity of cadmium to air breathing fish Heteropneustes fossilis (Osteoglossidae)

Abstract

Compost manure contains humic acid which can chelate metals in water and reduce toxicity and bioavialability. Static (180 day) bioassays were made in outdoor cement tanks (300 liters) with air breathing fish Heteropneustes fossilis exposed to 2.5 mgliter^‐1 cadmium (Cd) treated individuallly and with three different levels of compost manure made from fresh water macrophyte Pistia stratiotes. Addition of compost manure significantly reduced the concentrations of dissolved Cd in water and whole body Cd in fish and plankton. For quick removal of Cd from water a high dose of the manure (6.7 guter^‐1) was found more effective than a moderate dose (1.0 g‐liter^‐1) or cumulative treatment at moderate dose (1.0 gliter^‐1month^‐1). The cumulative treatment appeared more effective in reducing whole body concentrations of Cd when exposure was continued for a long period. Growth of fish, in respect of length, weight, and yield were reduced by Cd exposure. Addition of compost manure reduced the ill effects on growth to fish produced by Cd. The high dose of manure immediately resulted a superfluous increase in dissolved inorganic nutrients (NO₃‐N, NO₂‐N, NH₃‐N, PO₄‐P) and primary productivity. Water quality remained within optimum levels recommended for most aquaculture practices when the manure was added at a moderate dose (either once or every month). However, H. fossilis could tolerate water highly enriched in dissolved inorganic nutrients. Compost manure proved to be a promising tool to counter Cd toxicity in aquaculture, but to avoid organic enrichment a proper dose should be determined according to the condition available.

Key words:

• Cadmium
• Accumulation
• Chelation
• Compost
• Plankton
• Toxicity
• Growth