Most koi keepers optimise for the visible things — body shape, colour depth, size at sale. The invisible things get attention only when something goes wrong: a bacterial outbreak after a water change, fin rot after seasonal temperature swings, unexplained lethargy in an otherwise healthy tank.
By then, the damage is already happening.
The 2023–2024 university feeding trial conducted by UCSI University and Universiti Putra Malaysia didn’t just measure how fast koi grew on the BSF-based diet. It went inside the liver tissue — the primary hub of a fish’s immune and metabolic function — and mapped what was actually happening at the genetic level using mRNA library sequencing.
What it found changes how you should think about what you put in your pond.
The fish on BSF feed were building a stronger alarm system
When koi were fed the BSF-based diet, the genetic data showed upregulation of Interleukin-8 (IL-8) and related immune receptor genes. In plain terms: the fish were producing more of the molecular signals that recruit white blood cells to infection sites faster.
Think of it as the difference between a fire station that responds in two minutes versus one that responds in ten. The pathogen doesn’t disappear, but the window in which it can do serious damage closes much faster.
The complement system genes — specifically Complement C3 — were also significantly upregulated. This is part of the innate immune system, the first line of response that identifies and marks pathogens for destruction before your fish shows any outward signs of illness. Stronger complement activity means threats get neutralised earlier, before they cascade into visible disease.
Oxidative stress is the silent killer in ornamental tanks
Water changes, filter maintenance, seasonal temperature drops — every one of these events introduces oxidative stress into your fish. Oxidative stress generates free radicals that damage cell membranes, trigger internal inflammation, and quietly degrade organ function over time. Your fish can look fine on the surface while accumulating cellular damage underneath.
The UCSI/UPM research found that koi fed the BSF-based diet showed significant upregulation of glutathione-producing genes — including Glutathione S-Transferase variants that are directly involved in neutralising free radicals at the cellular level. Glutathione is the body’s primary internal antioxidant. More of it means faster recovery from environmental stress and less cumulative cellular damage between maintenance events.
For premium koi keepers doing regular water changes and seasonal pond management, this is not a minor benefit. It’s the difference between fish that bounce back quickly and fish that slowly decline without an obvious cause.
What this means practically
The BSF-based diet didn’t just grow the fish faster in this trial — it changed what was happening inside the fish at a biological level. Better immune signalling, stronger innate defense, higher antioxidant capacity. These aren’t marketing claims attached to the product after the fact. They came out of gene sequencing on liver samples from the actual trial animals.
TATSUMI is built on this research foundation. The growth and FCR numbers get most of the attention — and they should, because they’re remarkable. But for a keeper investing in premium stock, the immune and stress-resistance data may be the more important story.
A koi that grows fast but crashes under pressure is not a good investment. A koi that grows fast and handles its environment better is.
