DIETARY DEFICIENCY OF DOCOSAHEXAENOIC ACID IMPAIRS VISION AT LOW-LIGHT INTENSITIES IN JUVENILE HERRING (CLUPEA-HARENGUS L)

In the retina of herring (Clupea harengus L.), rods are recruited from about 8 wk after hatching, and from this time there is a linear relat ionship between the number of rods in the photoreceptor cell populatio n and the content of di22:6n-3 molecular species of phospholipids. Juv enile herring were reared from four weeks' post-hatching for 15 wk on either Artemia nauplii deficient in 22:6n-3 or on enriched Artemia nau plii containing 4.3% 22:6n-3. The visual performance of the fish was t hen determined at three light intensities (0.01, 0.1, and 1.0 lux) by observing their frequency of striking at live Artemia nauplii using in frared video recording. Herring reared on the diet containing no 22:6n -3 were less active predators, especially at the lowest light intensit y where very few strikes were observed. The eyes of these fish contain ed greatly reduced levels of di22:6n-3 molecular species of total phos pholipid, 2.1% vs. 12.0% in fish supplemented with 22:6n-3. The contri bution of saturated and monounsaturated fatty acids in the molecular s pecies of phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylcholine (PC) was virtually unchanged, while 20:5n-3 and 22 :5n-3 largely replaced 22:6n-3. There was an almost complete disappear ance of di22:6n-3 PC, while the amounts of di22:6n-3 PE and PS fell by 18.1 and 20.6% to 2.7 and 7.6%, respectively. The dipolyunsaturated m olecular species di20:5n-3, 20:5n-3/22:5n-3, and di22:5n-3 made up a s ubstantial part of the deficit. We conclude that a dietary deficiency of 22:6n-3 during the period early in rod development impairs visual p erformance such that the fish can no longer feed at low light intensit ies.