Fish, chitin, and chitosan production 293Estimated total fish yield = 5 ha x 3,270 kg/(ha-year) = 16,350 kg/year
Calculate DO at dawn (DOd) from Equation 6.5:DOd = 10.745 exp [-(0.017t + 0.002 Lc)] (6.5)
t = 90 days
Lc = Cumulative COD loading in pond = 50 x 0.125 x 90 = 562.5 kg/
(1250 m^3 pond volume)
= 90 kg/(200 m^3 pond volume)
DOd = 10.745 exp [-(0.017x90 + 0.002x90)] = 1.94 mg/LTilapia should be able to survive at this DOd level of about 2 mg/L. Or
organic loading to this fish pond can be a little more than 50 kg COD/(ha-day)
because Tilapia can tolerate DO level of about 1 mg/L.
6.6 Utilization of waste-grown fish
Waste-grown fish may be used as:
- A source of animal protein in human diet
- Fish meal or feed for other animals
6.6.1 Human consumption
The fish to be used for human consumption should be bigger in size, safe from
pathogens and helminths, and have nutrition equal to or higher that obtained
from other sources of fish. Size can be obtained by increasing the nitrogen
loading, lengthening the rearing period, and using a lower stocking density or
stocking with monosex male fish.
The following measures are believed to reduce the transfer of pathogens such
as: raising carnivorous fish for human consumption using the herbivorous fish
from waste-fed ponds as feed; pretreatment of waste input so that its
microbiological quality meets the standards for aquacultural reuse stated in
Table 2.28; depuration which is a natural process to remove some
microorganisms or toxic and malodorous compounds from the fish body by
putting contaminated fish in clean water for 1-2 weeks; and finally public
education to wash, to remove intestines and to cook the fish well before
consumption. Nutritional value of waste-grown fish has shown to be better than
those grown using other sources of feed. Most of the nutrition applied in the
form of waste is converted to protein rather than fat as reported by Moav et al.
(1977) and Wohlfarth and Schroeder (1979).