Natural Carotenoids from Photosynthetic Bacteria: Enriched Moina Sp. Enhances Coloration of Siamese Fighting Fish

Abstract

Siamese fighting fish (Betta splendens) cannot synthesize carotenoids and depend on dietary sources for body coloration, while synthetic pigments are costly and raise environmental concerns. This study evaluated Moina sp. enriched with photosynthetic bacteria (PSB) as a natural carotenoid carrier and its effects on growth, coloration, survival, and water quality. Moina sp. was immersed in a PSB suspension
(5.0 × 10⁴ cfu/mL) for 60 min and fed once daily for eight weeks to male red and blue fish (five fish of each color per treatment); control fish received non-enriched Moina sp. Enrichment raised the carotenoid content of Moina sp. from 2.54 ± 0.22 to 3.38 ± 0.48 mg/g, whereas crude protein (62.90 vs. 65.99%) and crude fat (3.09 vs. 3.67%) did not differ significantly (p > 0.05). Weight gain (0.32–0.41 g) and specific growth rate (0.56–0.68%/day) were similar among groups (p > 0.05). Survival was 100% in all groups except the red control fish (60%). After eight weeks, redness of blue fish increased by 64% with enriched Moina sp. compared with 42% in the control, and greenness increased by 64% versus 56% in red fish and by 24% versus 6% in blue fish. Water quality remained within suitable ranges in both treatments (pH 7.0–8.3; ammonia ≤ 0.03 mg/L; nitrite ≤ 0.19 mg/L). PSB-enriched Moina sp. is a natural live feed that enhances coloration and supports survival of B. splendens without impairing growth or water quality, offering a natural microbial alternative to synthetic pigments for safer, more sustainable ornamental aquaculture.