Growth rate of Limapontia capitata was determined at various temperatures and salinities. An optimal temperature of about 15 °C was found on the basis of growth rate, percentage of nongrowing animals during the experiments, spawning, and heart rate measurements. Q₁₀ of heart rates shows a high value in the temperature interval immediately preceeding maximum heart rate. This indicates a marked increase in respiration without a corresponding increase in growth. Heat coma sets in at 38-40 °C, and cold coma is estimated to set in around 0 °C. In late summer and early autumn, when the experimental animals were collected, the estimated mean water temperature in the sampling area is about 15 °C. Based on the same factors as above (no heart rate measurements), an optimal salinity of about 30 ‰ was determined. This is far from the mean of the sampling area (about 15 ‰), and spawning is as abundant (or more so) at 20 and 15 ‰, so some kind of adaption to salinity - although not with respect to growth - seems to exist. Death of osmotic stress only occurred at room temperature (20-23 °C) and a concurrent salinity of 5 ‰.