Enhancement of Fish Growth Employing Feed Supplemented with Recombinant Fish Growth Hormone Expressed in Bacillus Subtilis

Abstract

The application of fish growth hormone (FGH) to improving growth rates of fish has been a popular research topic in fish industry. Among various FGH, the tilapia (Oreochromis hornorum) growth hormone (tiGH) has captured much attention. Recombinant forms of tiGH have been expressed and employed to promote growth of not only teleost species of tilapia but also other fish such as sockeye salmon, larvae of tilapia, goldfish, trout and juveniles of carp and angelfish. In this communication, we report the use of an engineered Bacillussubtilis (well reputed as GRAS) system to express recombinant tiGH (rtiGH) which contained a 6-histidine tag at its C-terminus (rtiGH) in the cytoplasm of its B. subtilis host. The identity of rtiGH was confirmed by Western blot analysis and mass spectrometry. Using the whole cell lysate of B. subtilis comprising rtiGH, a facile method of preparing fish feed with rtiGH was developed. The efficacy of the supplemented feed was compared with that of normal feed in promoting fish growth in a randomized controlled study, employing Japanese koi as the fish model. Over the 4 months of study, the fish fed with supplemented feed (Treated group) and those with normal feed (Control group) did not display a differential preference between the 2 kinds of feed. Both groups of fish appeared to respond negatively to various effects of acclimatization in the first 2 months of the study. However, as judged by differences in overall average increases in body weight and length between the treated group (40.38g and 2.17cm respectively) and the control group (31.58g and 1.61cm respectively), it was concluded that the fish in treated group grew significantly faster than those in the control group. The fish fed with supplemented feed were shown to be healthy and physically welldeveloped, active and eager for food at all times.