From experience all the males I have had they are more stocky then females. From what I have seen males grow alot faster then the females The kok varies on each fish male and female its all genetics and as far as fertility goes I say its 50/50. Out of the 4 I have had 2 were able to get the job done the other 2 shot blanks. I try to breed at least 3 times b4 I make the decision