Study summary · Koi · Dietary pigments · Controlled feeding trial
Promising colour results, with limited replication
An eight-week koi trial compared nine diets. Spirulina improved growth and skin redness relative to control; paprika and a synthetic astaxanthin additive also improved redness. Only two tanks received each diet, limiting confidence in how repeatable these findings are.
Why this study matters
Colour is a common reason for choosing koi food. This study helps examine that particular claim, while keeping colour separate from welfare, disease prevention and lifespan.
How the study worked
Participants
360 red-and-white koi (Cyprinus carpio var. koi), initially averaging 22.9 g, were allocated to 18 freshwater tanks, 20 fish per tank. Water temperature was 27°C.
What happened?
Eight diets supplied different pigment sources, including 10% spirulina, 5% paprika and a Carophyll Pink astaxanthin additive. Feeding lasted eight weeks.
The comparison
A control diet without the added pigment sources; two replicate tanks per diet.
What was measured?
Growth, feed efficiency, survival and instrument-measured skin colour, among other outcomes.
What the researchers found
| Outcome | Reported result | How to read it |
|---|---|---|
| Growth | Higher with spirulina than control. | One small experiment; replication at tank level matters. |
| Skin redness | Higher with spirulina, paprika and Carophyll Pink than control. | A colour outcome, not a general health outcome. |
| Survival | No significant difference between diets. | Do not claim a survival benefit. |
Species and setting: Koi carp · Freshwater · Controlled laboratory tanks. Pond applicability remains uncertain.
Related ingredients
What strengthens the evidence?
A direct koi experiment with a control and instrumental colour measurement is more informative for this question than product testimonials. Separate diets also allow ingredient-specific comparisons, unlike a single mixture containing several colour additives.
What limits the conclusions?
There were only two tanks per diet. Fish sharing a tank are not independent replicates of the dietary treatment, so the total fish count can give a misleading impression of precision. Eight weeks in controlled tanks does not establish long-term performance in garden ponds. This review used the repository full text and English abstract, without raw-data reanalysis. The abstract and main text report carotenoid findings inconsistently; we do not rely on that outcome. The tested additive sources and inclusion levels cannot be assumed equivalent to an unspecified retail formula.
What the researchers concluded
The authors supported spirulina for growth and redness and paprika for redness under the tested conditions.
Evidence.pet interpretation
This is relevant ingredient research for koi, with substantial limits on generalisation. A retail label listing spirulina or astaxanthin does not tell us whether the dose, source, background diet or fish population matches this trial. Redder skin is not evidence of better overall health. The experimental percentages are study details, not home-feeding instructions. None of the Hikari foods profiled on Evidence.pet was tested here.
Funding and author interests
No funding or competing-interest statement was identified in the accessible repository text. That absence does not establish financial independence.
Read the original research
Kim YO, Lee SM. Effect of Dietary Carotenoids Sources on Growth and Skin Color of Red- and White-colored Fancy Carp Cyprinus carpio var. koi. Korean Journal of Fisheries and Aquatic Sciences. 2014;47(6):790–795. doi:10.5657/KFAS.2014.0790.
Evidence.pet editorial summary · Study ID STU-017 · Source checked 23 September 2026. Strengths, limitations and interpretation are our editorial assessment, not a formal evidence grade.
Source: Kim and Lee (2014). This is an original Evidence.pet editorial summary. The repository identifies the paper as CC BY-NC; no figures or tables are reproduced.