. Boletin de la Sociedad de BiologÃ-a de Concepción. Sociedad de BiologÃ-a de Concepción; Biology; Biology. Bol. Soc. Biol. Concepción. Chile. Tomo 62, 1991 can be influenced by many factors: temperature (CHlPMAN, 1947); chemical characteristics of the water and sediment (engle, 1957; peddicord. 1977), spawning (korringa, 1952; sastry, 1977) and food availability (korringa, 1952 op. cit., HAUKIOJA & HAKALA, 1978) among others. Diplodon chilensis chilensis (GRAY, 1828) which is largely distributed in lakes and rivers in the south of Chile, is a hyriid bivalve characterized by its toieran
. Boletin de la Sociedad de BiologÃ-a de Concepción. Sociedad de BiologÃ-a de Concepción; Biology; Biology. Bol. Soc. Biol. Concepción. Chile. Tomo 62, 1991 can be influenced by many factors: temperature (CHlPMAN, 1947); chemical characteristics of the water and sediment (engle, 1957; peddicord. 1977), spawning (korringa, 1952; sastry, 1977) and food availability (korringa, 1952 op. cit., HAUKIOJA & HAKALA, 1978) among others. Diplodon chilensis chilensis (GRAY, 1828) which is largely distributed in lakes and rivers in the south of Chile, is a hyriid bivalve characterized by its toierance to temperature and oxygen changes, and by its great filter - effectiveness (BUSSE, 1970). It is a gonochoric, ovoviviparous species with a continuous gonadal activity and seasonal reproduction but without an external sexual dimorphism (peredo & PARADA 1984, 1986). Ecological studies conducted by LARA& parada (1988) in La Poza Station, Lake Villarrica, have indicated that in spite of inhabiting sandy and muddy substrata, Diplodon chilensis chilensis is more abundant in muddy water-bottoms, situation which could eventually reflect a higher availability of food resources at mud substrata and explain the animal's fat state or condition index. The purpose of this study was to determine seasonally the condition index of D. ch. chilensis inhabiting different environments (sand and mud) and to relate it with the nature of the substrate, density and availability of resources. MATERIALS AND METHODS Through seasonal self-diving, at La Poza station in Lake Villarrica seasonally from August 1986 to April 1987, biológica! and abiotic samples were taken from áreas with sand substrate (ruditic sand) and mud substrate (muddy sand), located at dephts which due to the lake rainfall ranged from 0,5-5,0 m and 5,0-8,5 m, respectively during the year. During each sampling, 100 individuáis from both áreas were collected by hand and held in the laboratory at a temperature
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