Biology Reference
In-Depth Information
maximizing carbon mineralization to carbon dioxide to minimize
sludge accumulation; maximizing primary productivity that stimulates
shrimp production and also secondary crops;
optimizing nitrifi cation rates to keep low ammonia concentration;
optimizing denitrifi cation rates to eliminate excess nitrogen from
ponds as nitrogen gas;
maximizing sulphide oxidation to reduce accumulation of hydrogen
sulphide; and
maintaining a diverse and stable pond community where undesirable
species do not become dominant.
WASTE PRODUCTION IN FISH AND SHRIMP CULTURE
SYSTEMS
The physical, chemical and biological conditions of the culture environment
have an infl uence on the health and productivity of fi sh and shrimp.
Exposure of fi sh and shrimps to toxins like ammonia, carbon dioxide
and hydrogen sulphide lead to stress and ultimately disease. The types
of wastes produced in aquaculture farms are basically similar. However,
there are differences in quality and quantity of components depending
on the species cultured and the culture practices adopted. The wastes in
hatcheries or aquaculture farms can be categorized as: (1) residual food
and faecal mater; (2) metabolic by-products; (3) residues of pesticides;
(4) fertilizer derived wastes; (5) wastes produced during moulting; and
(6) collapsing algal blooms (Sharma and Scheeno, 1999).
Microbial Remediation of Organic Detritus
Organic detritus is accumulated in aquaculture ponds because of excess
feeds, faeces and dead algae. Aeration by itself is not enough to decompose
these organic detritus. Active bacterial populations must be changed to
species that are adapted to rapid degradation of complex organic matter.
Members of the genus
Bacillus,
i.e.,
Bacillus subtilis, B. licheniformis
,
B. cereus
,
B. coagulans,
and
B. polymyxa
are good examples of bacteria suitable for
microbial remediation of organic detritus. However, these are not normally
present in the required amounts in the water column, their natural habitat
being the sediment. When certain
Bacillus
strains are added to the water
frequently and at high density, they degrade organic matter faster than in
situations where only the natural populations are available. As a part of
bio-augmentation, the
Bacillus
can be produced, mixed with sand, clay,
rice husk and wheat bran or cow dung and broadcasted to be deposited at
the bottom of the pond. These bacteria produce a variety of enzymes that
break down proteins and starch to small molecules, which are then taken
up as energy sources by other organisms. The removal of large organic
