The scales of T. esculenta bear a series of clearly defined rings. These rings may be interpreted as growth indicators of the hypothesis that they are laid down as a result of breeding activity. The evidence supporting this hypothesis is discussed. In this form the data can be fitted to Von Bertalanffy's equation of growth. This itself supports the contention that the rings are laid down regularly, although in practice this is obscured by the fact that some breeding fish are to found throughout the year. Defining the growth rate of this species in terms of the parameters K and L? it has been shown that K, the rate of deceleration of an individual. There are simultaneous trends in the magnitude of these parameters; as the length at which maturation occurs increases, the value of K decreases and is at the same inversely related to the asymptotic length of the fish. It is also probable, in view of the maturation of artificial populations, that these variations are also related to the age of maturation. This is being investigated further. The above variations occurs within a population but comparison of the data from different areas of Lake Victoria shows that there are significant differences in the order of magnitude of K in the different areas, although the values of L? are comparable. In this form the parameters may be incorporated into further analyses of the population dynamics of the species. Comparison of the different areas sampled shows that the value of K of fish within the Kovirondo Gulf is significantly higher than elsewhere in the lake. The variations in the parameters defining the growth provides an explanation of the occurrence of ‘giant’ fish in the Emin Pasha Gulf area. Fish are fully grown at approximately ten years of age but at the present time the level of exploitation of the stock is such that in the northern areas of Lake Victoria very few fish survive more than four years in the exploited phase. Owing to the possible variation of the time of breeding within any one year, these data cannot be used for the detailed analysis of the growth of any one individual; at present it is not possible to age the fish from the time of hatching.
- 1 - sciences appliquees, technologies et medecines
- 2 - sciences biologiques et medicales
- 3 - sciences biologiques fondamentales et appliquees. psychologie