Multiple invertebrates possess enzymes enabling de novo biosynthesis of essential omega-3 fatty acids.

No abstract

Virtually all polyunsaturated fatty acids (PUFA) originate from primary producers but can be modified by bioconversions as they pass up the food chain in a process termed trophic upgrading. Therefore, although the main primary producers of PUFA in the marine environment are microalgae, higher trophic levels have metabolic pathways that can produce novel and unique PUFA. However, little is known about the pathways of PUFA biosynthesis and metabolism in the levels between primary producers and fish that are largely filled by invertebrates. It has become increasingly apparent that, in addition to trophic upgrading, de novo synthesis of PUFA is possible in some lower animals. The unequivocal identification of PUFA biosynthetic pathways in many invertebrates is complicated by the presence of other organisms within them. These organisms include bacteria and algae with PUFA biosynthesis pathways, and range from intestinal flora to symbiotic relationships that can involve PUFA translocation to host organisms. This emphasizes the importance of studying biosynthetic pathways at a molecular level, and the continual expansion of genomic resources and advances in molecular analysis is facilitating this. The present paper highlights recent research into the molecular and biochemical mechanisms of PUFA biosynthesis in marine invertebrates, particularly focusing on cephalopod molluscs.

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 relationship between the number of rods in the photoreceptor cell population and the content of di22:6n-3 molecular species of phospholipids. Juvenile herring were reared from four weeks' post-hatching for 15 wk on either Artemia nauplii deficient in 22:6n-3 or on enriched Artemia nauplii containing 4.3% 22:6n-3. The visual performance of the fish was then determined at three light intensities (0.01, 0.1, and 1.0 lux) by observing their frequency of striking at live Artemia nauplii using infrared video recording. Herring reared on the diet containing no 22:6n-3 were less active predators, especially at the lowest light intensity where very few strikes were observed. The eyes of these fish contained greatly reduced levels of di22:6n-3 molecular species of total phospholipid, 2.1% vs. 12.0% in fish supplemented with 22:6n-3. The contribution of saturated and monounsaturated fatty acids in the molecular species 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 disappearance 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 molecular species di20:5n-3, 20:5n-3/22:5n-3, and di22:5n-3 made up a substantial part of the deficit. We conclude that a dietary deficiency of 22:6n-3 during the period early in rod development impairs visual performance such that the fish can no longer feed at low light intensities.