The Biology and Culture of Tilapias

Tilapias in Fish Communities

Formerly Overseas Research Service

(Present address: c/o Fish Section. British Museum (Natural History)

Cromwell Rd., South Kensington, London, S. W. 7, England)

LOWE-MCCONNELL. R.H. 1982. Tilapias in fish communities, p. 83-113. In

R.S.V. Pullin and R.H. Lowe-McConnell (eds.) The biology and culture of

tilapias. ICLARM Conference Proceedings 7, 432 p. International Center

for Living Aquatic Resources Management, Manila, Philippines.

This paper reviews the information available on the ecology and behavior

of tilapias in natural fish communities, the species inte~actions and factors

controlling tilapia numbers, particularly conditions under which tilapias switch

from growth to reproduction. Maturation and maximum sizes tend to be

smaller (i.e., the fish 'dwarf') in small bodies of water than in larger ones, and

populations of fish with low weight for length switch to reproduction at a

smaller size than whose in which the fish are in better condition. Males tend

to grow larger than females in 'dwarf' populations, even in species in which

the two sexes grow to con~parable sizes in large lakes.

Comparison of tilapia growth rates from different lakes and rivers shows

that within a water body the various species grow at different rates, the

faster-growing species reaching a larger size. But the same species will grow at

different rates in different water bodies, suggesting that environmental

differences are more potent than genetic ones in determining maturation and

maximum sizes.

Studies of biomass, production, yield and turnover rates from the Kafue

floodplain and Lake Kariba show that only a small part of the total production

is cropped as yield in natural waters; the turnover rate (production/biomass

ratio) is higher in the substrate-spawning Tilapia rendalli than in the associated

mouthbrooding Sarotherodon. Studies in the equatorial Lake George (Uganda)

have shown that the highest yield of tilapia from a natural water body is

comparable with yields from unfertilized fishponds. But despite this high

sustained yield here, it represents less than 1% of the very high primary

production (blue-green algae on which the tilapia feed).

The great plasticity of tilapia growth in natural waters suggests that

concentrating research on environmental and behavioral factors affecting

growth and the switch to reproduction is likely to be more helpful for tilapia

culture than the search for faster-growing genetic strains.

Introduction

For this meeting I had been asked to review work on the behavior of
tilapias in natural fish communities and species interactions, to see if any
inferences could be drawn from this for tilapia culture in polyculture systems.
But as feeding and breeding behavior, microhabitats and the dynamics of
spatial segregation have already been reviewed in an earlier paper (Philippart
and Ruwet, this volume) the emphasis in this paper has been changed to