THE APPEARANCE OF RODS IN THE EYES OF HERRING AND INCREASED DI-DOCOSAHEXAENOYL MOLECULAR-SPECIES OF PHOSPHOLIPIDS

The retina of larval herring (Clupea harengus L.) contains only cones, with rods recruited progressively from about eight weeks onwards. The molecular species composition of phospholipids from the eyes of herring of different ages was determined to find whether the appearance of di-docosahexaenoyl molecular species (di22:6n-3) of phospholipids, which are characteristic of rod outer segment membranes in higher vertebrates, coincided with the appearance of rods. In the eyes of larval herring (cone-only retina) di22:6n-3 molecular species comprised 25.9% of phosphatidylethanolamine (PE), 22.9% of phosphatidylserine (PS) and 4.2% of phosphatidylcholine (PC). In the eyes of adult herring (rod:cone ratio of about 20:1) the proportion of di22:6n-3 molecular species had increased to 49.5%, 39.0% and 16.8% in PE, PS and PC, respectively. Juvenile herring had intermediate values of di22:6n-3 phospholipids. The results confirm the hypothesis that the amounts of di22:6n-3 molecular species of phospholipids in retina increase during development as rods appear, and also show that cones contain smaller amounts of these unique lipids. Three other molecular species containing docosahexaenoic acid, 16:0/22:6n-3,18:1/22:6n-3 and 18:0/22:6n-3 were also major components of eye phospholipids, emphasizing the important role of 22:6n-3 in vision.