Technical Abstract: Inhibition of the growth axis by somatostatin was studied in juvenile rainbow trout using passive immunization with a previously isolated somatostatin antibody (antiSS-14). Upon subcutaneously injection of laying hens (Gallus domesticus) with conjugated somatostatin-14 (SS-14), the antiSS-14 was isolated from egg yolk. Isolation of immunoglobulin was carried out at 40 d, revealing maximum IgY titre (IgY) at 3.22 ± 0.08 compared to control (0.1 ± 0.04) and highest total protein of 183 ± 2 mg ml-1 compared to the control (85 ± 3 mg ml-1). Passive immunization with extracted IgY at a dilution of 1:25 increased GH plasma concentrations after 30 min, reaching a maximum at 35 ± 7 ng ml-1 after 120 min. GH remained elevated for over a day, returning to baseline at 2 d. At 1:100, GH increased and returned to normal after 2d. . At 1:25, IGF-I plasma concentrations were increased at 30 min (277± 74 ng ml-1, p<0.05), 120 min (212 ± 77 ng ml-1,p>0.05), 240 min (359 ± 172 ng ml-1, p<0.05) and 1 d (259 ±117 ng ml-1, p<0.05) compared to the control (n=7, Tukey Test), returning to baseline levels after 2 d (145 ± 45 ng ml-1). In the 1:100 treatment group, slightly elevated GH did not induce IGF-I, which fluctuated between 13 8± 15 ng ml-1 and 167 ± 35 ng ml-1 (n =7, p>0.05) compared to the control fish, ranging from 131 ± 10 ng ml-1 to 148 ± 6 ng ml-1. Passive immunization thus demonstrates up regulation of plasma GH and IGF-I, suggesting the blockage of SS-14 mediated growth inhibition. The simplicity of antiSS-14 production in chicken eggs applied even suggests a potential use for growth promotion in aquaculture.