The Biology and Culture of Tilapias

The other major advantages of cage culture include relatively high growth
rates due to the continuous water exchanges, the limited space requirements,
the production of large fish of a more uniform size than pond systems, and
the possibility of greatly reducing production costs through a more precise
adjustment of feeding rates.

Table 15 summarizes the major constraints to culturing tilapias in cages.

The relative importance of these varies with location. The most important

water quality parameter is the DO. Low DO'S may appear once or twice a

year as a periodical feature of the lirnnological cycle of the water body. At

water temperatures from 26 to 30°C, special measures should be taken if the

DO of surface water drops below 3 mg/L for several consecutive days,

including lowered DFR or cessation of feeding and reduction in stocking

density. In Lake Kossou, heavy S. niloticus mortalities have been recorded

when DO'S suddenly fell to 0.4 mg/L (Traore and Campbell 1976). Important

mortalities in pond cages have also been observed for S. aureus following

a DO reduction (Pagh 1973). This could be caused, in certain cases, by the

cages and fish themselves, for example, in water bodies where the water

circulation is limited, where the total cage volume has become proportion-

Table 15. Constraints to the cage culture of tilapias and suggested remedial action.

Constraint

and target Remedial action

A. Environmental

1 Water quality Modify the culture technique

2 Weather Site selection/Anchoring system

3 Wild fi populations Control wild fish populations

4 Aquatic predators Control/Materials selection/Barrier

B. Inputs

1 Equipment

2 FryIFingerlings

3 Fish feeds

Design/Construction/Durability /Cost

Develop new methodology for mass production

Formulation/Develop production methods

C. Fish Stocks

1 Diseases/Parasites Site selection/Control wild fishIManagement

2 Security Site selection/Full time watchmen

3 Marketing Transport/Processing/Organization

D. Policy

1 Research

2 Planning

3 Development

Financial support/Training

Environmental potential/Inputs availability/

Market potential

Control/Extension service