A band of approximately 50-5 1 kDa, corresponding to glial fibrillary acidic protein (GFAP), was detected by immunoblot techniques in the brain tissue of Sparus aurata L. The levels of GFAP immunoreactivity were determined at three different stages of development: 6 month old, 18 month old and adults reared in an aquaculture facility for 3-4 years. Our results indicated a decrease of GFAP levels during S. aurata development from six month old to adult individuals. An explanation for this observation is suggested.