The Ruby Grain Surprise: How a Traditional Supplement Alters Betta Fish Biology

Beauty with Hidden Vulnerabilities

With their flowing fins and vibrant colors, Siamese fighting fish (Betta splendens) dominate home aquariums worldwide. Yet behind their beauty lies a delicate biological balance easily disrupted by dietary changes. For decades, aquaculture has turned to traditional supplements like red monascal rice—a fermented rice product believed to enhance color and vitality. But a landmark Thai study reveals this ruby-hued grain triggers unexpected effects in bettas, from stunted growth to reproductive disruptions 1 . This research challenges long-held assumptions about feed safety and offers crucial insights for fish breeders and scientists alike.

Betta fish

Siamese fighting fish are popular for their vibrant colors but sensitive to dietary changes.

Decoding Red Monascal Rice: Tradition vs. Science

Red monascal rice (RMR) forms through fermenting white rice with Monascus purpureus yeast. Historically used in Asian medicine and aquaculture, producers value it for:

  • Natural pigments (anthocyanins) that intensify fish coloration
  • Putative health benefits, including antimicrobial properties
  • Cost-effectiveness compared to synthetic supplements

However, its bioactive compounds—especially monacolin K and citrinin—exert powerful biological effects. While safe for humans at low doses, their impact on small fish like bettas remained unknown until rigorous testing began 1 .

Traditional Uses of RMR
  • Asian medicine for centuries
  • Natural food coloring
  • Aquaculture supplement
Potential Concerns
  • Contains monacolin K
  • May contain citrinin
  • Effects on small fish unknown

The Critical Experiment: RMR's Multisystem Impact on Bettas

In 2013, researchers at Prince of Songkla University launched a six-week investigation into RMR's effects. Using 300 adult bettas, they designed five diets with increasing RMR concentrations (0%, 0.25%, 0.50%, 1.00%, 2.00%) in a completely randomized trial 1 .

Methodology Step-by-Step:

  1. Feed Preparation: Commercial pellets coated with RMR suspensions at target concentrations
  2. Growth Tracking: Biweekly measurements of body weight/length and specific growth rate (SGR)
  3. Digestive Analysis: Enzyme assays (amylase, protease, lipase) from dissected intestines
  4. Reproductive Assessment: Oocyte RNA/protein ratios and maturation stages in females
  5. Tissue Analysis: Muscle biochemistry and whole-body fatty acid profiling
Experimental Design

The study used 300 adult bettas divided into 5 groups with different RMR concentrations (0%, 0.25%, 0.50%, 1.00%, 2.00%) fed for six weeks. All other conditions were kept identical to isolate the effects of RMR supplementation 1 .

Growth Performance vs. RMR Concentration

RMR Dose (%) Final Weight (g) Specific Growth Rate Significance vs. Control
0.00 (Control) 1.98 ± 0.15 2.15 ± 0.08 Baseline
0.25 1.92 ± 0.13 2.08 ± 0.07 P > 0.05 (no difference)
0.50 1.75 ± 0.11 1.82 ± 0.06 P < 0.001
1.00 1.63 ± 0.09 1.70 ± 0.05 P < 0.001
2.00 1.49 ± 0.12 1.55 ± 0.04 P < 0.001
Key Results
  • Growth Suppression: Doses >0.5% caused dose-dependent weight loss, with 2% RMR fish weighing 25% less than controls 1 .
  • Digestive Disruption: Amylase and protease activity plunged by 30–40%, crippling carbohydrate/protein digestion. Paradoxically, lipase spiked 22%, suggesting metabolic compensation 1 .
  • Reproductive Anomalies: Oocytes showed elevated RNA concentrations and altered RNA/protein ratios, indicating disrupted maturation 1 .
Digestive Enzyme Changes at 2% RMR
Enzyme Activity Change Biological Consequence
Amylase ↓ 38% Reduced carbohydrate digestion
Total Protease ↓ 41% Impaired protein breakdown
Trypsin ↓ 37% Limited protein absorption
Chymotrypsin ↓ 34% Reduced peptide cleavage
Lipase ↑ 22% Compensatory fat metabolism activation

Stealth Contaminants: While fatty acid profiles stayed stable, RMR introduced trace citrinin (a mycotoxin)—a known endocrine disruptor in vertebrates 1 .

The Scientist's Toolkit: Decoding Fish Feed Experiments

Reagent/Material Function in Experiments Example in Betta Study
Red Monascal Rice Test supplement; contains monacolins & pigments Coated pellets at 0.25–2.00% doses
Enzyme Assay Kits Quantify digestive enzyme activities Measured amylase/protease suppression
RNA Extraction Kits Isolate RNA from oocytes/muscle Assessed oocyte maturation disruption
Fatty Acid Profiling Analyze lipid composition in tissues Confirmed stable fats despite RMR
Citrinin ELISA Kits Detect mycotoxin contaminants Identified trace citrinin in RMR

Beyond Bettas: The Bigger Picture of Feed Safety

This study exposes a critical gap in aquaculture: traditional supplements ≠ safe supplements. While RMR's pigments benefit fish marketing, its biological costs remain hidden:

Growth-Reproduction Trade-offs

Energy diverted to detoxification may explain stunted growth and abnormal oocytes 1 .

Invisible Contaminants

Like the mercury detected in commercial fish feeds , RMR's citrinin could accumulate up the food chain.

Species-Specific Effects

Bettas' small size makes them vulnerable; larger fish may tolerate higher doses.

Conclusion: Rethink, Refine, Replace

The ruby glow of monascal rice in betta feeds masks a complex biological toll. While doses ≤0.25% appear safe, higher concentrations disrupt the very systems that keep these fish thriving. This research underscores a vital mandate: validate traditional supplements with modern science. As aquaculture evolves, replacing risky ingredients with toxin-free alternatives—like algal carotenoids for coloration—becomes essential. For now, betta breeders should scrutinize feed labels, because sometimes, what looks like a treasure is actually a trial.

"A supplement's history never guarantees its safety—only rigorous testing does."
– Adapted from the Thai research team 1

References