GONADOTROPIN-RELEASING HORMONES, INCLUDING A NOVEL FORM, IN SNOOK CENTROPOMUS-UNDECIMALIS, IN COMPARISON WITH FORMS IN BLACK-SEA BASS CENTROPRISTIS-STRIATA

The molecular forms of gonadotropin-releasing hormone (GnRH) in brain-pituitary extracts were determined for snook Centropomus undecimalis and black sea bass Centropristis striata. The extracts were analyzed in both isocratic and gradient high performance liquid chromatography (HPLC) programs. Eluted fractions were tested in radioimmunoassays with 4 different antisera made against 3 distinct GnRH peptides. Results show that snook contain 3 forms of GnRH, all of which are present in males and females irrespective of the stage of the reproductive cycle. Larger quantities of these GnRH peptides are present in snook in the nonreproductive phase than in snook in the reproductive phase. One form of snook GnRH is immunologically and chromatographically similar to salmon GnRH, and a second form is similar to chicken GnRH-II. However, the third snook GnRH appears to be distinct from the 7 known forms of the vertebrate hormone. In contrast, sea bass contain only the salmon GnRH-like and chicken GnRH-II-like forms of GnRH and, hence, appear to match the more usual pattern of GnRH peptides in teleosts. We speculate that one of the GnRH genes was duplicated and then altered in a fish ancestral to snook but not sea bass, even though both species of fish are in the recently evolved Perciformes order.