Noun:
	organic substances that are necessary for normal health and growth in higher forms of animal life.

Prostaglandins and leukotrienes are the 2  main tyes of eicosanoids that are found in fish

Both n-3 and n-6 fatty acids can be converted in the body into hormone-like substances that are known as eicosanoids. These are involved in a range of activities in the body including smooth muscle contraction, blood clotting, regulation of the immune system and inflammatory reactions.

Prostaglandins (including prostacyclins and thromboxanes) and leukotrienes are the 2 main types of eicosanoids.

These compounds are produced from fatty acids through a series of enzyme reactions. Bothe the n-6 and n-3 fatty acids use the same pathway of enzymes. As a result, they compete with each other for entry into this pathway. Eicosanoids exert very different effects depending on which family of fatty acids they are produced from. In general, those derived from n-3 PUFA are much less owerful than those derived from n-6 PUFA.

When the diet is low in fish oil, arachidonic acid is used as the substrate compound for this pathway and, in general, very powerful eicosanoids are produced. If the diet is rich is fish oil, then EPA competes with arachidonic acid and generally results in the production of much less harmful eicosanoids.

EXAMPLES OF EICOSANOIDS AND THEIR ACTIONS
Lekotrienes are involved in inflammatory responses
PUFA				EICOSANOID
20:4 n-6 Arachidonic acid				Leukotriene B4 (LTB4) which is a very powerful inflammatory agent
20:5 n-3 EPA				Leukotriene B5 (LTB5) which is at least 30 times less powerful than LTB4 at producing an inflammatory response
Thromboxane is involved in platelet aggregation
20:4 n-6 Arachidonic acid				Thromboxane A2 (TXA2) has a strong effect on stimulating platelet aggregation
20:5 n-3 EPA				Thromboxane A3 (TXA3) has a very weak effect on platelet aggregation

based on the documentation of "Nutritional Aspects of Fish" prepared by the Irish Sea Fisheries Board (AN BORD IASCAIGH MHARA)