Biocontrol of ammonia pollution in the rearing water of fish by inducing a heterotrophic bacterial-based food chain in the medium

摘要

In intensive aquaculture, one of the main problems confronted by the farmers is the ammonia pollution and subsequent disease outbreaks, high costs of quality protein feed, and the labor for periodic water exchange. Ammonia is a major metabolic waste product from fish, which is excreted across the gill membranes and in the urine. Controlling the inorganic nitrogen by manipulating the carbonitrogen ratios seems to be a practical and inexpensive means of reducing the accumulation of ammonia. At high carbon to nitrogen (C/N) ratios, bacteria will assimilate nitrogen, i.e., ammonia, from water and produce new cell protein. The experiment was designed by adding 0, 10, 20, and 30 g of carbohydrate (rice flour) for each gram of total ammonia nitrogen (TAN) released as a result of feeding metabolism and feed waste decomposition. The ammonia built up in the rearing water showed a drastic decrease in all the carbohydrate added tanks. The heterotrophic bacterial growth was significantly higher in the same. The biochemical constituents and growth rate were higher in fishes in the tanks having C/N ratio 10 and 20. Percentage weight gain was 100% for T-30, protein efficiency ratio (PER) was high for T-20 and T-30 (4.048). The C/N ratios of 20 and 30 worked more effectively. Shifting the aquatic ecology from autotrophic to heterotrophic bacterial-based community can improve water quality and recycle the toxic ammonia waste to heterotrophic bacterial flocs, which in turn can be consumed by the fish, thereby reducing the feed protein demand and subsequently the reduction of feed cost.