If you’ve followed the first three posts in this series, you already know what the 2023–2024 UCSI and UPM feeding trial showed significant improve on weight gain FCR for koi compared to commercial feed, and statistically significant colour improvement from the BSF and dragon fruit peel combination.
This post is about why the same nutritional logic applies to fancy goldfish — and what that means practically for Ranchu, Oranda, and Ryukin keepers.
Goldfish and koi share more biology than most keepers realise
Goldfish (Carassius auratus) and koi (Cyprinus rubrofuscus) are both members of the family Cyprinidae. They share the same ancestral feeding pattern — omnivorous, with a natural diet heavy in aquatic insects, larvae, and organic bottom matter. This is directly relevant to why BSF protein performs the way it does in fish nutrition.
The conventional koi and goldfish feed industry built itself around fishmeal as the primary protein source because it was abundant, cheap, and reasonably effective. It was never because fishmeal is biologically optimal for these species. BSF protein more closely mirrors what cyprinid fish would eat in a natural environment — which is precisely why the gene sequencing data from the UCSI/UPM trial showed upregulation of digestion enzymes and immune markers in response to it. The fish body responds differently to protein it recognises.
Ranchus, Orandas, Ryukins — the fancy varieties that command premium prices — have been selectively bred for body characteristics that make them more nutritionally demanding than common goldfish, not less.
The compressed, rounded body shape means their internal organs occupy less space. Digestive tract, swim bladder, and liver are all working in a tighter arrangement. Poor protein digestibility in this context doesn’t just mean slower growth — it means undigested protein breaking down in the gut, increased gas production, and the kind of buoyancy issues that are the most common cause of loss in fancy goldfish collections.
This is where BSF protein’s digestibility profile matters beyond just the FCR number. The UCSI/UPM trial showed upregulation of Chymotrypsin-like Protease — a key enzyme responsible for breaking dietary protein into absorbable peptides — in koi fed the BSF-based diet. More complete protein breakdown means less undigested matter moving through the digestive tract. For a Ranchu with a compressed gut, that is not a minor benefit.
Growth: the same protein logic, applied to a different body type
Fancy goldfish are judged on body depth, head growth, finnage, and overall proportion — not just size. These structural characteristics are genetic, but they require adequate protein to express fully during the juvenile growth phase. A Ranchu that receives inadequate protein in its first six months will not recover that structural potential in adulthood.
The koi trial showed that the BSF-based diet produced 17.10g weight gain versus 7.42g on commercial feed over 42 days, with an SGR of 1.20% per day versus 0.63%. The mechanism behind those numbers — higher bioavailability, better digestive gene expression, more efficient nutrient absorption — applies across cyprinid species. Your Ranchu’s growth rate and body development are directly tied to how much of the protein in every pellet it can actually use.
Colour: what the research showed and what it means for goldfish
The second feeding trial from the UCSI/UPM research added red dragon fruit peel to the optimised BSF base. Over 45 days, the BSF plus dragon fruit peel group showed statistically significant redness enhancement. The commercial feed group showed none.
Goldfish, like koi, cannot produce their own carotenoid pigments. Everything that determines the depth and vibrancy of a Ryukin’s red patches or an Oranda’s colour pattern comes entirely from the diet. The betacyanin compounds in red dragon fruit peel provide a natural pigment pathway that the fish body can uptake and deposit — without synthetic astaxanthin.
The colour data in the research was measured on koi, not goldfish. The pigmentation biology is shared across cyprinids, but the specific colour response in fancy goldfish varieties will depend on each fish’s genetic colour potential. What the nutrition does is provide the raw material for that potential to express — it doesn’t create colour where genetics don’t support it.
What this means for feeding TATSUMI to fancy goldfish
TATSUMI is formulated on the BSF protein and red dragon fruit peel base validated in the UCSI/UPM research. The nutritional logic — high-bioavailability BSF protein, natural pigment pathway, digestive efficiency — transfers to fancy goldfish through shared cyprinid biology.
Feed 2–3 times daily during active growing periods, only as much as your fish can consume in five minutes. For fancy varieties prone to buoyancy issues, smaller and more frequent feeds are preferable to one large feeding — this reduces the volume of food entering the compressed digestive tract at once.
The structural and colour development you’re working toward with your Ranchu or Oranda collection starts with what’s in the pellet. Everything else is management.
