The researchers studied the lipids in the pineal organ of rainbow trout to see if they play a role in controlling daily rhythms. They found that the main type of lipid was triacylglycerols, and phosphatidylcholine was the most common polar lipid. The fatty acids in the lipids were mostly saturated, monounsaturated, and polyunsaturated. The pineal organ had a similar lipid composition to the retina, with phosphatidylinositol being a key lipid. This suggests that the pineal organ may have a similar function to the retina in the fish's body.