DEVELOPMENT OF A RADIOIMMUNOASSAY FOR EUROPEAN EEL GROWTH-HORMONE ANDAPPLICATION TO THE STUDY OF SILVERING AND EXPERIMENTAL FASTING

A specific and sensitive homologous radioimmunoassay for eel (Anguilla anguilla L.) growth hormone (angGH) has been developed. The antiserum , raised against purified angGH and used at 1:20,000 final dilution, d id not crossreact with eel prolactin or thyrotropin, carp gonadotropin II, bovine GH, or serum from hypophysectomized eel. The inhibition cu rves for eel pituitary extracts and serum were parallel to that of ang GH standard. The ED50 value was between 1 and 2 ng/tube and the recove ry of purified angGH added to the serum was about 100%. In immunocytoc hemical studies, the antiserum, used at 1:1000 dilution, specifically labeled the somatotrophs in the pituitaries of the glass, yellow, and silver eels. The GH contents were determined in the pituitaries of gla ss, yellow, and silver eels and in the serum at the yellow and silver stages. GH variations during the transformation of the yellow to silve r eel were examined. The results indicated a decrease in GH production between the yellow and the silver eels, possibly related to the cessa tion of growth at the silver stage. In contrast to the situation in th e naturally fasting silver eel, submitting yellow eels to 3 months of starvation (experimental fasting) greatly increased GH production. Thi s suggests a variation in the regulation of GH according to the type o f fasting (natural or experimental) and/or the stage of the fish (yell ow or silver). (C) 1996 Academic Press, Inc