During the late postspawning phase, freshwater catfish Clarias batrachus fed a diet rich in linseed oil (18 : 3 n-3) (LSO) and 13L : 11D photoperiod and at 28 C showed increases in ovarian weight and plasma levels of testosterone and oestradiol-17 , and in concentrations of free fatty acids (FFA), monoglycerides (MG), diglycerides (DG), triglycerides (TG), phospholipids (PL) and esterified cholesterol (CE) in the liver, plasma and ovary. In fish fed a diet rich in sunflower oil (18 : 2 n-6) (SFO) under the same conditions, plasma testosterone decreased sharply, concentrations of FFA, DG and TG increased in the liver and plasma and ovarian levels of TG and CE decreased. Neither diet was gonadostimulatory when fed at 18 C. 2000 The Fisheries Society of the British Isles