The Biology and Culture of Tilapias

Diseases of Tilapias

R. J. ROBERTS AND C. SOMMERVILLE

Institute of Aquaculture

University of Stirling

Stirling, Scotland

ROBERTS. R.J. AND C. SOMMERVILLE. 1982. Diseases of tilapias, p. 247-263.

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.

Studies on intensively cultured and wild tilapias have shown that although

they are more resistant to diseases than many other species, there is never-

theless a wide range of disease problems which can occur. To date no viral

problems other than lymphocystis have been recorded. The bacterial patho-

gens include aeromonads, myxobacteria and particularly Edwardsiella tarda.

A wide range of parasitic problems occur including particularly trichodinids,

Zchthyophthirius and various intermediate stages of digenea?! flukes. Nutri-

tional problems are a major difficulty in intensive culture, with aflatoxicosis a

major cause of losses associated with poor quality storage of food ingredients.

Introduction

There are two principal reasons why diseases of the tilapias (genera
Tilapia and Sarotherodon) have been less well studied than those of many
other groups of cultured fishes. The first is that such fish are generally
farmed in countries where diagnostic facilities are less than adequately
developed, so that losses cannot be investigated properly; the second is that
the culture of tilapias has only been intensified recently. At low stocking
densities, environmental water quality is usually high and opportunities for
infections to build up are thus limited. Equally, the observation of disease
conditions is much more difficult at low densities in large water bodies than
under the controlled conditions of the high density tank or cage systems.
Most of the early observations on diseases of tilapias have related to
parasitic infections, often from wild fish and at low levels (Khalil 1971;
Sarig 1971). These have generally shown no evidence of clinical effects on
the fish and in most wild populations of tilapias it would seem that para-
sitism is a normal occurrence of little consequence. The present paper is
restricted to a review of diseases of tilapias which occur in culture systems or
those of wild fishes which have a clinical manifestation or potential signi-
ficance for culture. Although the literature has been surveyed, and references
are quoted where relevant, the majority of the information has been derived
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