A sensitive radioimmunoassay (RIA) was used for detection of circulating insulin-like growth factor-I in juvenile fish of Persian sturgeon. This assay was validated by obtaining parallelism between standard curve and serum dilutions. In order to detection any possible relationship between IGF-I and growth performance, circulating IGF-I in four age classes (1-4 year old) of cultured juvenile Persian sturgeon were measured. Moreover biometrical parameters such as total weight, total length, fork length and condition factor (K), were measured which could represent growth performance in juveniles. IGF-I concentrations increased simultaneously with age increase, but there were no significant differences between each age classes (p<0.05). Biometrical traits also significantly varied with age. The established relations between IGF-I and biometrical traits had shown significant positive correlations for IGF-I ver total weight, total length and fork length (P<0.05). The present data for the first time showed the relation between circulating IGF-I and a possible role of this peptide in growth performance in a chondrostean.
