Forty-two adult Cab males, tested for fertility, were treated in groups of seven fish in 300 ml of 3 mM ENU (Nethyl-N-nitrosourea,N-3385, Sigma) with 0.03% sea salt solution adjusted to pH 6.3 with 1 mM phosphate buffer for 1 h. at 268C and subsequently allowed to recover for 2 h. in recovery solution (tap water, 0.0001% Methylene blue) with an exchange of the solution after 1 h.