The ecological conversion efficiencies of 8 fish species in the Yellow Sea and the Bohai Sea and main influence factors were studied by laboratory and in situ methods. Moreover, results determined by laboratory method were compared with those by in situ one. The results showed that : (1) There were significant differences among ecological conversion efficiencies of 8 fish species. The change range of food or energy conversion efficiencies of the fishes were 12. 9 % -39. 0 % or 14. 8 % -46. 1 % respectively. (2) Both of the specific growth rates and ecological conversion efficiencies changed along with differences of following ecological and physiological factors , such as temperature , body weight , feeding level , food species and social behavior etc. The ecological conversion efficiencies tended to show inverted ”U ”change with rise of temperature and feeding level , and decelerating decrease with body weight increment. The feeding levels and specific growth rates could be significantly changed by differences of food species and social behavior , but energy conversion efficiencies could not. (3) There were significant differences , which changed with different fish species , between the results determined by laboratory and in situ methods.