Biotin-deficient grass carp had reduced antimicrobial peptide expression and weakened immune responses across multiple organs, with optimal levels at 0.21–0.25 mg/kg diet.
5 AMPs reducedby biotin deficiency in grass carp — LEAP-2A, LEAP-2B, hepcidin, beta-defensin-1, and mucin 2
What the researchers found
Biotin deficiency at 0.012 mg/kg diet caused a cascade of immune impairments across the head kidney, spleen, and skin of grass carp:
Antimicrobial peptides were reduced: LEAP-2A, LEAP-2B, hepcidin, beta-defensin-1, and mucin 2 all had lower mRNA levels. These peptides form the first line of defense against bacterial invasion.
Innate immune function declined: lysozyme activity, acid phosphatase activity, complement C3 and C4, and immunoglobulin M all decreased.
Inflammation went up: pro-inflammatory cytokines (IL-1beta, IL-6, IL-8, IL-12p40, IL-15, IL-17D, TNF-alpha, IFN-gamma2) increased through NF-kB signaling. Anti-inflammatory cytokines (IL-4/13A, IL-10, IL-11, TGF-beta1) decreased through impaired TOR signaling.
Optimal biotin levels for growth, lesion prevention, and immune function ranged from 0.210 to 0.245 mg/kg diet.
Why it matters
Grass carp is the most farmed freshwater fish in the world. Biotin is a common feed additive but optimal levels for immune function were unknown. This study shows biotin is not just a growth vitamin; it directly supports antimicrobial peptide production and balanced immune responses. Biotin deficiency creates a double problem: weaker antimicrobial defense and more damaging inflammation.
The numbers in context
540 fish; 6 biotin levels; 70 days + 6-day challenge; 5 AMPs reduced; optimal 0.21-0.25 mg/kg
How the study worked
Controlled feeding trial with 540 grass carp (starting weight ~117g) fed six biotin levels (0.012 to 0.518 mg/kg) for 70 days. After the feeding period, fish were challenged with Aeromonas hydrophila for 6 days. Gene expression, enzyme activities, and immune markers measured in head kidney, spleen, and skin.
Who was studied
540 grass carp (Ctenopharyngodon idella), ~117g starting weight
What this study cannot tell us
Only grass carp were tested; results may not apply to other fish species. The extreme biotin deficiency level (0.012 mg/kg) is unlikely in commercial feeds, though suboptimal levels are possible. Gene expression changes do not always translate to proportional protein level changes. The bacterial challenge used a single pathogen.
How to read the evidence
Moderate evidence from a well-designed feeding trial with 540 fish, six biotin levels, and a bacterial challenge test.
When this study was published
Published in 2020. Nutritional immunology in aquaculture continues to inform feed formulation standards.
The bigger picture
Grass carp is the world's most farmed freshwater fish. This study shows biotin is not just a growth vitamin — it is essential for immune defense. Ensuring optimal biotin in fish feed could reduce disease outbreaks and antibiotic use in aquaculture.
Questions still open
- Do other B vitamins have similar effects on fish antimicrobial peptides?
- Is the optimal immune biotin level different from the optimal growth level?
- Can biotin supplementation reduce antibiotic use in commercial fish farms?
Common questions
Why does biotin affect immune defense in fish?
How does this help fish farming?
Read the original research
Dietary biotin deficiency decreased growth performance and impaired the immune function of the head kidney, spleen and skin in on-growing grass carp (Ctenopharyngodon idella).
Fish & shellfish immunology, 97, 216-234
Citation
He, Peng; Jiang, Wei-Dan; Liu, Xiang-An; Feng, Lin; Wu, Pei; Liu, Yang; Jiang, Jun; Tan, Bei-Ping; Yang, Qi-Hui; Kuang, Sheng-Yao; Tang, Ling; Zhou, Xiao-Qiu. (2020). Dietary biotin deficiency decreased growth performance and impaired the immune function of the head kidney, spleen and skin in on-growing grass carp (Ctenopharyngodon idella).. Fish & shellfish immunology, 97, 216-234. https://doi.org/10.1016/j.fsi.2019.12.033