General and Comparative Endocrinology 102, 360–369 (1996) Article No. 0079 Development of a Radioimmunoassay for European Eel Growth Hormone and Application to the Study of Silvering and Experimental Fasting Jacques Marchelidon,* Monika Schmitz,* Louis M. Houdebine,† Bernadette Vidal,* Nadine Le Belle,* and Sylvie Dufour* * Muse ´um National d’Histoire Naturelle, Laboratoire de Physiologie Ge ´ne ´rale et Compare ´e, URA CNRS No. 90, 7 rue Cuvier, 75005 Paris, France; and † INRA, Laboratoire de Biologie Cellulaire et Mole ´culaire, Ba ˆtiment des Biotechnologies, 78352 Jouy-en-Josas Cedex, France Accepted January 19, 1996 In teleosts, growth hormone (GH) has been suggested A specific and sensitive homologous radioimmunoassay to be involved in various physiological functions in- for eel (Anguilla anguilla L.) growth hormone (angGH) has cluding growth (Donaldson et al., 1979; McLean et al., been developed. The antiserum, raised against purified 1990), osmoregulation (Clarke et al., 1977; Miwa and angGH and used at 1:20,000 final dilution, did not cross- Inui, 1985; Boeuf et al., 1990; Borski et al., 1994), and react with eel prolactin or thyrotropin, carp gonadotropin reproduction (Higgs et al., 1976; Singh et al., 1988; Van II, bovine GH, or serum from hypophysectomized eel. The der Kraak et al., 1990; Le Gac et al., 1992; Burzawa- inhibition curves for eel pituitary extracts and serum were Ge ´rard and Delevalle ´e-Fortier, 1992; Singh and parallel to that of angGH standard. The ED50 value was Thomas, 1993). In the life cycle of the European eel between 1 and 2 ng/tube and the recovery of purified (Fontaine, 1989; Lecomte-Finiger, 1990; Fontaine and angGH added to the serum was about 100%. In immunocy- Dufour, 1991), especially during the transformation of tochemical studies, the antiserum, used at 1:1000 dilution, the female yellow eel to silver eel, all these functions specifically labeled the somatotrophs in the pituitaries of are implicated. The yellow eels have a sedentary life in the glass, yellow, and silver eels. The GH contents were the river for 5 to 20 years, corresponding to a period determined in the pituitaries of glass, yellow, and silver of growth (Pankhurst, 1982). They are completely im- eels and in the serum at the yellow and silver stages. GH mature. This period ends with the silvering (change in variations during the transformation of the yellow to silver the color of the skin), which occurs before the reproduc- eel were examined. The results indicated a decrease in tive migration to the ocean. The silvering includes many GH production between the yellow and the silver eels, other changes such as a slight increase in the gonadoso- possibly related to the cessation of growth at the silver matic index of the female, as well as the appearance of stage. In contrast to the situation in the naturally fasting silver eel, submitting yellow eels to 3 months of starvation some characteristics that may suggest an ‘‘anticipation (experimental fasting) greatly increased GH production. adaptation’’ (Fontaine, 1983; Fontaine, 1994) to life in This suggests a variation in the regulation of GH according the deep sea: an increase in the ocular index, new retinal to the type of fasting (natural or experimental) and/or the pigments (Pankhurst and Lythgoe, 1983), modifications stage of the fish (yellow or silver).  1996 Academic Press, Inc. of the swimbladder red body (Kleckner and Krueger, 1981), and gill chloride cells (Fontaine et al., 1995). The 0016-6480/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved. 360