The growth of juvenile grass carp (initial weight :15 ～ 30 g/ind .) in dif ferent seasons was observed .The seasonal and daily var iat ions of ser um growth hormone of juvenile gr ass carp wer e me asured using a sandwich ELISA system for cyprinid GH .there was a significant se asonal var iat ion in growth ra tes of the juvenile grass carp , the highest growth rate was found in the fish sampled in June ,whereas the lowest growth rate was f ound in the winter .Serum growth hormone(GH)levels also vary on a seasonal basis with the GH level in April , and the lowest levels in February , September and November .In br eeding season , serum GH level in matured female grass carp markedly rised just befor e spawning induction and re tur ned to normal af ter spawning .A reproducible daily r hythm in ser um GH levels of the juvenile grass car p sampled in labor atory was present .The GH levels wer e generally higher at night than in the daytime , and a r emar kable pe ak appe ared at 24 :00 .