Fish, chitin, and chitosan production 263or animal manure is fed to fish ponds for the purpose of fish production. Most
fish farmers also add supplementary feed such as agricultural by-products and
grains to the fish ponds.
The second and third techniques of waste reuse in aquaculture have been
practiced in both developing and developed countries. There are about 2,500 ha
of sewage-fertilized fish ponds in Calcutta, India; 270 ha in Hunan, China; 233
ha in Munich, Germany; 50-100 ha in Israel; and a smaller-scale operation in
Hungary. When properly operated, the productivity of fish ponds using
wastewater has been found to be higher than that of inorganically fertilized
ponds (Allen and Hepher 1976).
Some reported yields of fish raised in waste-fed ponds in various countries
are shown in Table 6.1.
Another type of aquacultural waste that has high reuse potentials is shrimp
biowaste. Shrimp production is being done in several tropical countries such as
Thailand, Vietnam, Indonesia, India, China and Honduras. Thailand is currently
one of the largest shrimp producers with an estimated shrimp production in
2006 of 450,000 tons, about 10% of the total world production. The shrimp
biowaste, which is mostly shrimp shells, comprises about 40% of the total
shrimp production. Since shrimp shells contain about 10-20% chitin, the
production of chitin and chitosan from shrimp shells, as earlier stated in section
1.2.3, would bring economic returns and reduce pollution load resulting from
the disposal of shrimp biowaste to landfills.
The cultivation of fish in waste-fed ponds and production of chitin and
chitosan will be described in this chapter.
6.1 OBJECTIVES, BENEFITS AND LIMITATIONS OF
FISH CULTIVATION IN WASTE-FED PONDS
The main objectives and benefits that can be gained from waste recycling
through fish production are as follows:
6.1.1 Waste stabilization and nutrient recycling
Waste treatment is the primary objective of any waste recycling scheme and the
inclusion of fish production recovers nutrients in the waste, such as N, P and K.
Addition of waste or its by-products such as biogas slurry and compost to fish
pond resulted in increased fish yields (Polprasert et al. 1982). Due to the
economic value of fish, part of the waste treatment costs can be recovered. This
financial return will be an incentive for safe disposal of waste, which will lead
to better public health conditions, particularly among the rural people where
malnutrition and excreta-related diseases are common.