The Four Pillars of the Immune System in Fish- Eicosanoids

In previous articles, we introduced the four pillars of the immune system in fish: Power, Blood, Cell Walls and Eicosanoids. 

This article covers the eicosanoid system which acts as the communications network of the immune system using chemistry to make and receive signals.  We also cover the micronutrients needed to make a healthy eicosanoid system.

When any cell detects the presence of a foreign pathogen such as bacteria, viruses or sea lice it will send a  signal to the immune system for help. In response, the immune system increases blood flow/pressure to that region, releases white blood cells and even elevates temperature to slow a viral infection by telling the fish to move to warmer water. As the fish fights off the virus or recovers from a wound, anti-inflammatory signals dominate restoring the animal back to steady state.  

Eicosanoids are chemical signals and formed using fatty acids.  The pro-inflammatory signals are made using two Omega 6 fatty acids including arachidonic acid (AA).  Anti-inflammatory signals are made with AA and Omega 3 fatty acids.  

Fish make more omega VI eicosanoids than omega III, but the omega III have a much longer half life than the omega VI eicosanoids.  When attacked both are released.    After the proinflammatory response has proceeded and the omega VI eicosanoids fade, the omega III are there to resolve the inflammation with anti-inflammatory actions. For fish and humans the right ratio is one omega III to two or three omega VI.

Together with our sister company Sustainable Aquatics inc, we have tested over 40 commercially prepared hatchery feeds. In salmon, there has been a shift away from using wild caught fish (e.g. anchovies) ingredients to plant based sources of proteins and fats.  This shift increased the Omega 6 intake in some cases from 2 or 3 to 1 to 20:1 creating imbalances in the animal's ability to form the correct eicosanoids. 

There are three types of marine Omega 3 oils all in the linolenic acid family.  The least useful form is alpha-linolenic acid (ALA) with 18 carbons.  ALA is found in algae.  As animals develop they can upcycle ALA into more useful forms linolenic acid by adding carbons to the backbone. Eicosapentaenoic acid (EPA) has 20 carbons.   Docosahexaenoic acid (DHA) has 22 carbons.  The upcycling chemistry is highly inefficient. Most animals will get EPA and DHA directly from eating fatty fish or krill or DHA rich algae.

We always recommend selecting a hatchery feed supplemented with DHA to offset the loss DHA in commercial hatchery diets.

DHA will promote both growth as well as support a healthy eicosanoid system.

Arachidonic acid (AA) is mild antioxidant.  Whenever a fish comes under attack from a virus or pathogen, it starts its defense in the inflammatory state.  As we discussed in our recent blog about power,  fighting off viruses requires energy which in turn generates more reactive oxygen species (ROS).   AA and other antioxidants will mitigate ROS but if used for ROS mitigation then AA can’t be used to form eicosanoids.

Nature's most powerful antioxidant,  astaxanthin, in the proper form takes up residence in the cell and protects AA from being depleted by ROS. 

Ensure your hatchery feed or supplement contain natural astaxanthin in the 3S, 3’S form together with a delivery system that can move astaxanthin through the digestive tract and blood stream into the cell. 

Astaxanthin has to be nano-sized to be bioavailable and delivered with lipids or fats to help form blood soluble envelops to carry the compound through the blood and through the cell plasma membrane. 

Our sister hatchery has operated over 100 RAS systems for 15 years enjoying an over 96% egg hatch to harvest yield across 200 species of warm and cold water fish. All without antibiotics or vaccines. 
Dose your fish with the micronutrients their immune system needs to do its job and let nature do the rest. 

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