Ma. Rahman et al., Expression of a novel piscine growth hormone gene results in growth enhancement in transgenic tilapia (Oreochromis niloticus), TRANSGEN RE, 7(5), 1998, pp. 357-369
Several lines of transgenic G1 and G2 tilapia fish (Oreochromis niloticus)
have been produced following egg injection with gene constructs carrying gr
owth hormone coding sequences of fish origin. Using a construct in which an
ocean pout antifreeze promoter drives a chinook salmon growth hormone gene
, dramatic growth enhancement has been demonstrated, in which the mean weig
ht of the 7 month old G2 transgenic fish is more than three fold that of th
eir non transgenic siblings. Somewhat surprisingly G1 fish transgenic for a
construct consisting of a sockeye salmon metallothionein promoter spliced
to a sockeye salmon growth hormone gene exhibited no growth enhancement, al
though salmon transgenic for this construct do show greatly enhanced growth
. The growth enhanced transgenic lines were also strongly positive in a rad
io-immuno assay for the specific hormone in their serum, whereas the non gr
owth enhanced lines were negative. Attempts to induce expression from the m
etallothionein promoter by exposing fish to increased levels of zinc were a
lso unsuccessful.
Homozygous transgenic fish have been produced from the ocean pout antifreez
e/chinook salmon GH construct and preliminary trials suggest that their gro
wth performance is similar to that of the hemizygous transgenics. No abnorm
alities were apparent in the growth enhanced fish, although minor changes t
o skull shape and reduced fertility were noted in some fish. There is also
preliminary evidence for improved food conversion ratios when growth enhanc
ed transgenic tilapia are compared to their non-transgenic siblings.
The long term objective of this study is to produce lines of tilapia which
are both growth enhanced and sterile, so offering improved strains of this
important food fish for aquaculture.