Sustainable Aquaculture in the Estuary Area

Abstract

An estuary is the widening part of a river where it meets the sea, and is an interface between agriculture, forestry, animal husbandry, civilian life etc., where mangrove trees grow in the tropical and subtropical area. The leaves of mangrove and seaweeds, which grow close to the mangrove, are decomposed, adding enormous quantities of detritus to the estuary ecosystem. Because most of the energy flow through estuary food chains is derived from detritus, mangrove and seaweeds are major contributors to the productivity of the estuary. For example, the estuary place where the ratio of mangrove forest area/river area is high, the quantity of fish catch is much larger than the place where the ratios are low, and also bivalves are dominant in the area of the high ratio, but the polychaetes are dominating, in stead, in the low ratio area.
Based on these results, the microbial (detritus) food chain was adopted for the production of fish; that is, the bacteria which promoted the growth of fish are added with the conventional feed line in situ aquaculture. The bacterial strains were also selected to have the function to repress the pathogenic bacteria, fungi and viruses. With this method, the production rates of many fishes, prawn and crabs increased and also they were protected from pathogens. This method, in which microorganisms repress the pathogens, is called biological control or biocontrol and the useful microorganisms adopted are termed as biocontrol agents (BCAs).
Following the feeding of an artificial compound feed (ACF)/BCAs mixture to fish, the BCAs contained in residual ACF and feces after digestion sank to the sediment. Eventually, these bacteria degraded organic materials in the sediment.