APPLICATION OF A SENSITIVE RADIOIMMUNOASSAY FOR THE MEASUREMENT OF GROWTH-HORMONE IN GILTHEAD SEA BREAM (SPARUS-AURATA) AND OTHER SPARID FISH

The development of a homologous radioimmunoassay (RIA) for gilthead sea bream growth hormone (sbGH) is described. RIA sensitivity was 0.4 ng/mL, and ED50 was 1.74 +/- 0.05 ng/mL. Intra- and inter-assay coefficients of variation were 3.4 and 8.8%, respectively, at ED50 levels. Mammalian growth hormones (GH), carp gonadotropin, chinook salmon gonadotropin, ovine porlactin, and recombinant tilapia prolactin did not show cross-reactivity. Serial dilutions of recombinant trout GH indicated a low but significant cross-reactivity. The displacement curves for plasma and pituitary homogenates from sparid fish (gilthead sea bream, blacktail, white sea bream, Couch's sea bream, and marmor-brassen) were parallel to that of the sbGH standard. Pituitary homogenates from other perciform fish tested (gaper, grey mullet, red mullet, and sea pike) also-showed-parallel slopes of inhibition. Pituitary homogenates from common sole, sea scorpion, forked hake, goldfish, rainbow trout, and European eel showed low or negligible cross-reactivity. These results suggest that the GHs of perciform fish have a number of similarities in structure. RIA of sea bream GH can be used to quantify the GH of sparid fish and perciform fish, provided a validation has been carried out.