| Sumario: | Three experiments under laboratory condition were conducted to study the effect of temperature and female size, measured as prosome length and dry weight, on egg production and egg viability of Calanus chilensis Brodsky captured from the Bay of Mejillones, northern Chile. In the first experiment egg spawning was monitored every 2 hours in Females kept in individual vials at five constant temperatures. namely 9, 12, 15, 18 and 20 degrees C. In a second experiment, temperature was constant, 15 degrees C. Finally, a third experiment was conducted at three constant temperatures, 12, 15 and 20 degrees C under excess of food to determine temperature effects on egg production for a more extended period of rime. As food, a monoculture of Isochrysis galbana Parke was used For the first experiment and phytoplankton collected from tile same Bay cultured in F2 medium was used for the second and third experiments. In the first experiment clutch size (CS), defined as the total number of eggs laid at once within a 2 h period, ranged between 5 and 84 eggs female(-1). In most cases all the eggs were able to hatch and those that did not hatch were assumed as nonviable. CS was positively correlated to temperature, but only 2 out of 12 females were able to lay eggs at the lowest temperature (9 degrees C), whereas at the highest temperature (20 degrees C) CS tended to decline. There was a lack of synchrony in egg laying and no temperature effect on the number of nonviable eggs was detected. However a significant positive correlation between CS and the number of nonviable eggs was found (F-1,F-25=4.67, P<0.05). In the second experiment CS was highly variable, 36+/-degrees 18.67 (mean degrees S.D.) and not associated with either female length (F-1,F-26=1.86, P>0.05), or with female dry weight (F-1,F-26=0.026, P>0.05). Finally from the third experiment, egg production on a daily basis, was drastically reduced at 20 degrees C, while differences between 12 degrees C and 15 degrees C were not detected. Our results agree with previous studies indicating that egg production correlates positively with temperature. However, there appears to be an ''optimal temperature range'', within which maximal clutch sizes and daily egg production rates are attained. This temperature range coincides with that observed at the upper 10 m layer in the study area. This suggests that maximal egg production rates of this species would only take place at the upper layer. On the other hand, sharp population declines, such as that observed during ''El Nino'' 1991-92, may have been caused by abrupt changes in water temperature giving rise to a poor recruitment, because of depleted egg production taking place at temperatures greater than 20 degrees C.
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