The Biology and Culture of Tilapias

Genetic Markers in Samthemdon and Their Use

for Sex and Species Identification

Department of Life Sciences

Bar-Ilan University

Ramat-Gun, Israel

AVTALION. R.R. 1982. Genetic markers in Sarotherodon and their use for

sex and species identification, p. 269-277. 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.

Enzyme and other protein genetic markers in Sarotherodon and Tilapia

are reviewed with special emphasis on their use for the identification of species

and hybrids. Three different groups of markers: transferrins, esterases and

male sex-protein (MSP) were found to be useful for the control of Sarothero-

don parental breeding stocks used in Israel for the commercial production of

F1 all-male hybrids. Understandably, the tests for these markers were re-

stricted to serum proteins, which could be collected from broodstock without

damaging them. These serum markers were found to be species-specific,

providing a tool for the identification of both parents and their hybrids, and

therefore permitting the elimination of xenogeneic contaminants from the

breeding stock.

The possible biological importance of MSP is discussed as a sex and species-

specific marker and as a possible gene-product involved in sex regulation.

Finally, an autosomal theory of sex determination in Sarotherodon is sum-

marized and discussed.

Introduction

Sarotherodon species, the mouthbrooding tilapias, are currently being
cultured in fish ponds in tropical and subtropical countries, and constitute
an important source of animal protein in developing countries. A free-breed-
ing culture of tilapias in a limited water space gives rise to an enormous
quantity of small fish having no economical importance. Thus, the economic
feasibility of Samthemdon culture is essentially based on monosex culture
of males. However, the manual separation of males from females is expensive
and time consuming.
The culture of these fish made significant progress when it was shown
that hybridization between some unrelated species of this genus gives rise
to fertile F1-hybrid broods, which present unusual sex ratios, including
100% males. This result was consistently obtained by different authors
mainly in the crosses of S. mossambicus and S. niloticus 99 with S. hor-