GROWTH, CONDITION AND MORTALITY OF CHIROS TOMA-HUMBOLDTIANUM (ATHERINIFORMES, ATHERINIDAE) IN MEXICO

The silverside fish (Chirostoma humboldtianum) was studied at the San Felipe Tiacaque dam, Mexico state, Mexico. Sampling was done once duri ng each season of 1987, in three sampling stations at the shore with a 30 m long net (1.5 m ''hanging'', 0.8 cm aperture). Four age groups w ere determined (scale method). The growth rates were: spring -0.1778, summer-0.3364, fall =-0.2032 and winter -0.2869. Corresponding conditi on factors were 0.0170, 0.0101, 0.0071 and 0.0032, respectively. Morta lities were -2.5649, -1.2489, -1.1513 and -2.5649, respectively. Sprin g is the time of the highest condition factor and food abundance (the silverside is planktivorous) but also of lowest growth because resourc es are allocated to reproduction. Growth is concentrated in the summer . Al values are low in autumn when food is scarce and reach low peaks in winter, when nevertheless the fish is able to grow in length (but n ot in weight).