Six independen data sets (Tables 2,3) were analysed to assess the growth performance of hybrid offspring and thei parental control groups: Icommunual rearing in 1992-93, 104 day testing period (in this experiment all fish were individually tagged with passive (in this experiment all fish were individually tagged with passive integrated transponders, PIT tags); II separate rearing in 1992-93, 78 day testing period; III separate rearing in 1992-93 (part I)169 day testing period;