The Biology and Culture of Tilapias

Life Histories of Tilapias: An Evolutionary Perspective

D. L. G. NOAKES AND E. K. BALON

Department of Zoology

College of Biological Science

University of Guelph

Guelph, Ontario

Canada Nl G 2 W1

NOAKES. D.L.G. AND E.K. BALON. 1982. Life histories of tilapias: an evo-

lutionary perspective, p. 61-82. 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.

The early ontogenies of tilapias are shown to be of major importance in

the evolution of life history styles. By applying hierarchical systems for

classification of reproductive guilds, and a uniform system of categorization

for developmental intervals, we show that the life history styles of tilapias fall

into two clearly defined categories, altricial and precocial, and that a signifi-

cant evolutionary mechanism exists for changes between these. The major

evolutionary trend has been from a more altricial style, the nest-spawning

guarders (equivalent to substrate-spawners), to the more precocial style, the

mouthbrooding external bearing species (equivalent to mouthbrooders). The

major distinction between these is largely a consequence of heterochronous

shifts in ontogeny, particularly the lack of a larval period in the ontogeny of

the bearers. Asurvey of published information shows the predicted differences

between the two types of species, with some overlap. The overlap exists

because individual species retain the ability to adapt somewhat more towards

an altricial or a precocial life history style by ontogenetic shifts within their

own reproductive guild (i.e., guarder or bearer). This predicts the adaptive

responses expected of fish under varying ecological conditions, including

aquacultural practices. Stunting, perhaps the most serious problem in aqua-

culture, is not only interpreted in our theoretical framework, it is predicted

by us. We make some tentative suggestions as to how stocks of tilapias might

be manipulated to better purpose for aquaculture production.

I ask the reader to remember that what is most obvious may be most

worthy of analysis. Fertile vistas may open out when commonplace facts are

examined from a fresh point of view. L. L. Whyte (in Koestler 1967)

Introduction

This review of the life histories of tilapiine cichlid species of the breeding
morphs called Tilapia and Sarotherodon will focus in particular on early life
history and developmental features. We believe this approach brings profit-
able insights to the understanding of the biology of these fishes. We also