Aspects of the biology of Cichlasoma uropthalmus (Gunther) with particular reference to its culture

Abstract

This thesis is an investigation of the basic biology, reproductive behaviour, and key physiological and nutritional requirements of the Mexican and Central American cichlid Cichlasoma urophthalmus (Gunther), with particular reference to the potential of native species for aquaculture in the region. C. urophthalmus is a widely appreciated food fish within its native range, commanding good prices and having the advantage in terms of aquaculture that the risk from introduction of an exotic species with the consequent importation costs, diseases and escapes are eliminated. The dentition, gill rakers and gut structure are indicative of a carnivorous habit and this was corroborated by seasonal examination of gut contents which revealed that the species feeds principally on small animals. Investigation of the species in the natural environment suggest that growth was continuous, with some slight depression in the cooler winter months, reproduction occurred in the second year and the minimum reproductive size was 102cm (50g). In the laboratory C. urophthalmus grew well between 22.5 and 36.3°C the best growth being achieved at 32°C and optimum growth and survival (- production) being at 28°C. The species is typically euryhaline and can be acclimated to salinities of 0% to 35%. It can withstand instantaneous transfer from O to 15%, and reverse, and have best growth at 15%, probably due to the energy saving in an isotonic medium. Oxygen consumption rates were similar to other cichlids and C. urophthalmus can survive virtual anoxia for about 2h. C. urophthalmus is a bottom-spawner and the aggressive features of its reproductive behaviour, described in this work, can probably be minimized in culture. Its fecundity is about 5 to 7 times that of the mouth brooding tilapias, producing 2000-7000 eggs per spawn and it can reproduce at about 23 days intervals, probably throughout the year with management of temperature. Hatching is rapid (61 days) and survival good with simple hatchery techniques. Broodstock requirements, handling and labour costs could be lower than for the mouth brooding tilapias. The protein requirements of fry were shown to be 39-45% of the diet and this is similar to the tilapias. Diet digestibility was depressed by high dietary fibre content, but was not inhibited by inclusion of soybean (25.81%) or wheat meal (26.7%) in the diets. Although much more research is required. The results reported here have enabled tentative formulations of diets for aquaculture, based on typically available ingredients. The features of C. urophthalmus are discussed and compared extensively with those of the other cultured fish, principally the tilapias. It is concluded that C. urophthalmus is a very good candidate for aquaculture development within its range of distribution and that it has strong advantages over introduction of cultured cichlids.