266 Organic waste recycling: technology and management
6.1.4 Operational skill and maintenance
Fish culture does not require highly skilled manpower for its operation. Fish
harvesting is easier than algal harvesting. Fish processing is usually not required
for human consumption. For other uses such as animal feeds, drying is generally
sufficient.
However, fish production from wastes might have some or all of the
following limitations:
Land requirement and existence of a waste collection system
Land requirement for fish production is quite large as the organic loading to fish
ponds has to be low to avoid DO depletion at dawn. Land should be available at
low cost and closer to the source of waste and natural water courses (e.g. canals
or rivers). The transportation of waste should be safe, easy and cheap. If the
waste is available in a concentrated form such as septage, suitable sources of
water to make-up the evaporation and seepage losses should be available.
Table 6.2 Efficiency of feed utilization of various animal species per 1000 g of feed
intake (adapted from Hastings and Dickie 1972)
Species Live weight
gain (g)Food
conversion ratioEnergy gain
(kcal)Protein
gain (g)
Chicks
Pigs
Sheep
Steers
Channel catfish
Brown trout356
292
185
163
715
5762.8
3.4
5.4
6.1
1.4
1.7782
1492
832
748
935
608101
30
22
26
118
75Availability of suitable fish fry
Fish species suitable for stocking in waste-fed ponds should be available locally
at low price. If such facility for fish fry production is not available or its
production is not economically feasible locally, fish production is not possible.
Public health risks
Waste-grown fish have a potential to be contaminated with several kinds of
pathogens that may be present in the waste itself (Table 2.23). Fish growing in a
medium that has high concentrations of heavy metals or other toxic substances
may, through the processes of bioaccumulation and biomagnifications, contain
high concentrations of these substances in the fish tissue.