RG-92
RG-92 is the additive that KiGen uses in the Marujyu Special food
What is RG-92?
To provide the most honest picture possible of the RG-92 product, we have gathered as much information as possible and described it below.
RG92 in the context of the koi hobby
- RG92 is described by the producer (SARABiO 温泉微生物研究所 in Beppu) as a natural extract derived from a unique micro-alga (green alga) that lives in hot springs.
- It is therefore not a “classic” chemical additive, but a hot-spring algae extract that is also positioned as a feed ingredient in livestock farming and aquaculture.
- SARABiO also mentions (on their own site) that in 2021 it was classified as feed/飼料
Application in aquaculture (what is the objective)?
On the same page, SARABiO mentions that trials have been conducted in aquatic animals/aquaculture (including with hirame / flounder) and that these trials showed, among other things:
- Faster growth (増体促進)
- Lower mortality (へい死抑制)
- Better FCR / feed efficiency (増肉係数改善)
RG-92
How does RG92 get "into the fish"?
According to SARABiO’s FAQ, the standard administration is:
- By mixing it with the food.
- They also explicitly mention that it can (alternatively or additionally) be mixed with water and that it can be mixed with regular compound feed or drinking/breeding water.
Practical use in the farm/koi pond (what does that usually mean)?
In aquaculture, this almost always comes down to one of these routes in practice:
- Adding it into pellets (in the feed factory as a premix/ingredient in the recipe), or
- Top-dressing / coating on-site (mixing/coating extract over existing pellets just before feeding), or
- Via water administration (if the product is intended/stable for that; they suggest “water etc.” as an option).
RG-92
In close consultation with the producer of RG-92, KiGen has consciously chosen to mix RG-92 directly into the food. Thanks to its excellent heat resistance—the algae from which RG-92 is extracted originate from hot springs—this ingredient is ideally suited for application during the extrusion process.
The result of this choice is clear and consistent: RG-92 is present as a full ingredient in every single food pellet. This ensures even intake and maximum effectiveness with every feeding.
And from a biological perspective?
When mixed with food, RG92 enters via oral intake into:
- The gastrointestinal tract (where effects on gut health/inflammation/energy metabolism are claimed), and then
- (Depending on the active fractions) absorption through the gut to the rest of the body.
RG-92 Flowchart
Intake of RG-92 via food
↓
Release in the gastrointestinal tract
↓
Support of gut function & intestinal barrier
↓
Improved nutrient absorption (protein / fat / energy)
↓
Absorption of bioactive fractions via the gut
↓
More efficient energy metabolism at the cellular level
↓
Healthy growth + increased vitality + better resistance
RG-92 and heat: what does 90 °C during extrusion mean?
The answer to this question is obviously very important.
In the section on pro- and prebiotics, KiGen argues that living organisms largely or entirely die off during extrusion. KiGen does not want to market koi food that doesn’t do what we promise.
RG-92 is (according to the Japanese producer SARABiO) an extract of thermophilic micro-algae from hot springs (onsen) in Beppu. That is a major advantage here:
- The origin is an organism that naturally lives at elevated temperatures
- The active fractions are described as more heat- and pH-stable than many classic vitamins, enzymes, or probiotics
This makes RG-92 more suitable for extrusion than, for example, live bacteria or sensitive enzymes.
90 °C: a problem or not?
In feed technology, the rule of thumb is:
- 90 °C – briefly → usually acceptable for:
- Algae extracts
- Polysaccharides
- Certain lipid fractions
- Non-living bioactive components
- >120 °C or long residence time → often results in degradation
- KiGen food is heated to 90°C for 3 minutes
Does RG-92 remain biologically “active” after extrusion?
Important distinction:
RG-92 is not a probiotic (no living cells), so it doesn’t need to survive, it just needs to not break down chemically.
Probable mechanism of action (based on what SARABiO claims + comparable products):
- Metabolic modulation
- Gut health / anti-inflammatory effects
- Improved nutrient utilization (FCR)
- Possible effect on mitochondrial activity (this is often mentioned for RG-92 in livestock farming)
These are effects that:
- Are not dependent on living structures
- Are dependent on the structural integrity of extract components
Extrusion at 90 °C is therefore perfectly compatible with its function.
