PHYSIOLOGICAL-CHANGES IN THE JUVENILE EURYHALINE TELEOST, THE TILAPIAOREOCHROMIS-HORNORUM, INJECTED WITH E-COLI-DERIVED HOMOLOGOUS GROWTH-HORMONE

Growth is a complex process in fish. This study was designed to test t he effect of different levels of recombinant tilapia growth hormone (t iGH) injected intraperitoneally in juvenile hybrid tilapia Oreochromis hornorum. Tilapia GH cDNA was cloned from hybrid O. hornorum tilapia. The mature protein was expressed in E, coli under regulation of the p hage T7 promoter. The E. coli-derived tiGH was partially purified to 6 7% purity and, following renaturation, was shown to be biologically ac tive in in vivo and in vitro assays. Recombinant tiGH stimulated extra cellular matrix synthesis as shown by S-35-sulfate uptake in ceratobra nchial cartilage explants. Zero, 0.1, 0.5 and 2.5 mu g tiGH/g body wei ght (gbw) were injected in tilapia, and the effects on the growth-prom oting action, hepatosomatic index (HSI), and mRNA insulin-like growth factor (IGF) induction were measured. A significant increase in the bo dy weight (P < 0.05) and length (P < 0.01) was observed in tilapia rec eiving 0.5 mu g tiGH/gbw, However, tilapia receiving 0.1 and 2.5 mu g tiGH/gbw did not show an increase in body weight and length with respe ct to the control group receiving BSA injections. Binding sites for th e recombinant tiGH were identified in the liver. Consistent with its s omatotropic actions, the IGF mRNA induction was observed in the groups injected with 0.1 and 0.5 pg tiGH/gbw (P < 0.05). No significant incr ease in the HSI was detected in the injected groups when compared to t he control group. These results demonstrated that the injection of bio logically active E. coli-derived tiGH produces physiological changes i n juvenile tilapia that ultimately resulted in a growth-promoting acti on only at a dose of 0.5 mu g tiGH/gbw.