A 3-week feeding trial was conducted in medaka broodstock (age five months) to examine the effect of dietary arachidonic acid (ARA) level (range: 4-23 mg g-1 of total fatty acids (TFAs)) on fertility, cyclooxygenase (COX) activity, egg size, sperm motility parameters, hatching rate and weight of hatch, survival and growth of larvae. After spawn induction and dietary exposure to 4 mg ARA g-1 TFA, broodstock were fed a diet containing ARA in the amounts: 4 (continued, as control), 5, 14 and 23 mg g-1 TFA. COX1 activity in the liver and the number of COX2-positive cells in the ovaries was increased in females fed the diets containing the two highest amounts of ARA. The highest sperm motility parameters were observed in males fed a diet containing 23 mg ARA g-1 TFA. The hatchability rate and bodyweight of hatchlings were higher in the group obtained from broodstock fed a diet containing 23 mg ARA g-1 TFA (79% and 0.66 mg fish-1, respectively) compared with 4 mg ARA g-1 TFA (50% and 0.40 mg fish-1). The average mortality of offspring obtained from this group at 7 days post hatching was significantly higher than that of all other groups.
Keywords: Oryzias latipes; arachidonic acid; cyclooxygenases; larval quality; reproduction parameters.