Description:
<jats:p><jats:bold>SUMMARY.
</jats:bold> Between 1967 and 1977, catches of <jats:italic>Tilapia galilaea</jats:italic> in Lake Kinneret fell from an annual average of about 200 tonnes to a low of 70 tonnes in 1974, and then returned to their former level. Total yearly mortality (<jats:italic>Z</jats:italic>) was estimated at 1.84 between 1970 and 1976. Assuming a natural mortality (<jats:italic>M</jats:italic>) of 0.94, total stock size averaged 300–700 tonnes in that period, while recruitment averaged < 0.7–3 million per year. Three broods hatched in years of relatively high water levels (1970, 1971 and 1972) yielded especially low recruitment.</jats:p><jats:p>The Von Bertalanffy growth coefficient (<jats:italic>K</jats:italic>) was estimated at 0.67, and final length (L∞) at 25–36cm total length. First year's growth, 23–152mm, was closely related to final length, which appeared to be affected by genetic variation in the population. Yearly fluctuations in size distribution were attributed to changes in the proportions of fast‐ and slow‐growers, as well as in the abundance of year‐classes. Recruitment to the fishery, at 17–20cm, occurred between ages l+and3+.</jats:p><jats:p>The highest growth rates for age‐1 <jats:italic>T, galilaea</jats:italic>, 1–2% mean weight per day, occurred in April and May, the <jats:italic>Peridinium</jats:italic> season. However, only a small proportion of age‐1 fish reached marketable size by July, when their food supply began to diminish. During the autumn months, there was hardly any length increment, and all <jats:italic>T. galilaea</jats:italic> became lean, especially the age‐0 group. It is surmised that recruitment of stocked fish could be increased by introduction in December and by use of fingerlings which are potentially able to grow to marketable size in less than two seasons.</jats:p>