Aquaculture, 30 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (1983) 249-261 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands 249 zyxwvutsrq TILAPIA STOCK IDENTIFICATION USING ELECTROPHORETIC MARKERS B.J. McANDREW and K.C. MAJUMDAR Institute of Aquaculture, University of Stirling, Stirling (Great Britain) (Accepted 4 April 1982) ABSTRACT MeAndrew, B.J. and Majumdar, K.C., 1983. Tilapia stock identification using electro- phoretic markers. Aquaculture, 30: 249-261. With the difficulties in the identification of the many tilapia species, a reliable method independent of morphological characteristics was needed to define the nature of the cul- tured stocks throughout the world. Starch gel electrophoresis of various body tissues and the resolution of protein loci using specific histochemical techniques has shown that a large amount of co-dominant interspecific variation exists which may be used to identify unequivocally the nine different species studied. The technique and relevant buffer sys- tems and stains are described together with an account of the enzymes observed and their interpretation. The results are expressed as relative mobilities of the observed isozyme bands, allowing direct comparison between all the species studied. The potential of the technique is discussed regarding its possibilities in tilapia culture and in the general genetic improvement of stocks. INTRODUCTION Tilapia have become one of the main groups of cultured species in recent years. It has become apparent that with the many introductions and fish movements both worldwide and within the tilapia’s endemic range, there is great difficulty in identifying the actual nature of the fish species available. Many incidences of hybridization have been noted in natural water bodies, usually after introductions of non-endemic species (Trewavas, personal com- munication, 1980). Poor management of cultured stocks has allowed un- wanted hybridization of previously pure species to occur by escapes into the wild and vice versa. Despite the diversity of habitat and food requirements, the commercially important tilapia are remarkably similar in overall morphology with much emphasis placed on the breeding colouration of the adults in species identification. The morphological and meristic characters used in identifica- tion are of limited.value in that these characters often have overlapping distributions (see Fryer and Iles, 1972). Such characters are also affected by environmental factors, and with the widespread distribution of many species 0044-8486/83/0000-0000/$03.00 0 1983 Elsevier Scientific Publishing Company