AN ENZYME-IMMUNOASSAY FOR SALMON GONADOTROPIN-RELEASING-HORMONE AND ITS APPLICATION TO THE STUDY OF THE EFFECTS OF DIET ON BRAIN AND PITUITARY GNRH IN THE SEA BASS, DICENTRARCHUS-LABRAX

The effects of two different diets [diet 1 (D1), high protein-low carb ohydrate; diet 2 (D2), low protein-high carbohydrate] on brain and pit uitary gonadotropin-releasing hormone (GnRH) contents, as well as circ ulating steroids and vitellogenin, were studied over the reproductive period of the sea bass. Salmon GnRH was measured using a newly develop ed competitive enzyme immunoassay with an enzymatic tracer made of sGn RH covalently coupled to actetylcholinesterase from the electric organ of the eel Electrophorus electricus. The pituitary GnRH content of an imals of both sexes fed D1 was significantly reduced at the time of sp awning compared with the pre- and postspawning stages, whereas fish fe d D2 did not exhibit such changes. In the brain only minor differences in the GnRH content were observed between the two diets. It is conclu ded that GnRH release rather than synthesis is affected in fish fed a low protein-high carbohydrate regimen. Plasma sex steroids and vitello genin were not greatly affected by the diet. (C) 1994 Academic Press, Inc.