In the present experiments, the highest growth rate in 15 p.p.t. was accompanied by the
highest serum T, level and this trend is most apparent in fish fed high dietary protein levels.
This would suggest an involvement of T4 in growth promotion.
Optimal growth was observed for tilapia adapted to 15 p.p.t. and this was accompanied by high levels of circulating T4 (Woo et al., unpublished data).
Administration of T4 has been shown to enhance growth, development and survival in tilapia (Lam, 1980) and carp (Lam and Sharma, 1985).
Inclusion of T3 in the diet also produced significant increases in growth rate and food conversion efficiencies in the red sea bream (Woo et al., 1991) and tilapia (Howerton et al., 1992)