ABSTRACT: Short-term laboratory experiments were carried out to investigate the effect of water temperature on somatic growth rate of the jellyfish Aurelia aurita (L.). Medusae of A. aurita (2.24 to 32.0 g wet weight) with an initial excess foodsupply were kept at 1 of 4 temperatures (5.1, 10.0, 16.4 and 19.0°C). Daily weight-specific growth rate (G) for each individual medusa was calculated from growth of the subumbrellar area, which was estimated from image analysis of video recordedmedusae. Average value of G increased significantly with temperature, and ranged from 0.053 d^-1 at 5°C to 0.15 d^-1 at 16.5°C. The laboratory results were compared to in situ growth rates calculated from fieldobservations of change in size of medusae from Gullmarsfjorden, western Sweden, 1993 to 1996. Specific growth rates in situ ranged from 0.11 to 0.16 d^-1. Growth rates calculated from simulations of growth, based on laboratory-determinedtemperature-specific growth rates and surface water temperature in Gullmarsfjorden, were similar to or lower than in situ specific growth rates. In situ growth of A. aurita ceased in summer. This is suggested to be due to more energybeing allocated to reproduction than somatic growth, food shortage, or a genetically determined cessation of somatic growth after reproduction.