Both fish can have different growth rates. Some Endlis and BGKs grow faster than the other. Usually Endlis tend to slow down in growth around 6"-11" BGKs tend to slow down around 6"-8" My 10" BGK and 3 Endlis are doing fine with the Endlis ranging from 10"-11.5" My BGK was around 4" when I first got it and the Endlis were already at 7" Is your BGK pretty thin? Are you sure that the Endli was trying to eat the BGK and not trying to show dominance? You're BGK may need some fattening up. Anywhere for the BGK to hide in the tank?