1. Introduction

      With the growing demand for eco-friendly and sustainable aquaculture, microbial probiotics have become essential tools in modern farming. Bacillus subtilis, a safe and highly efficient probiotic strain, has been widely used in fish, shrimp, and crab farming. This article introduces the functions, application methods, and advantages of Bacillus subtilis in aquaculture, helping farmers improve water quality and farming performance.

2. Key Characteristics of Bacillus subtilis

1. High resistance and strong survival ability·
   Its spore structure allows it to withstand heat, acidity, and harsh environments.

2. Environmentally safe and non-toxic
   It is recognized as a safe probiotic for long-term use.

3. Rapid reproduction and strong competitive exclusion
   This helps beneficial bacteria dominate water and gut environments while inhibiting harmful microbes.

3. Major Functions in Aquaculture

1. Improving water quality by degrading organic matter

Bacillus subtilis produces enzymes such as protease, cellulase, and amylase, which help break down:

• leftover feed

• feces

• organic sludge

Effectively reducing ammonia, nitrite, and hydrogen sulfide levels.

2. Inhibiting harmful bacteria and stabilizing the micro-ecosystem

It helps suppress:

• Vibrio species

• E. coli

• fungi

thus preventing disease outbreaks and keeping the water environment stable.

3. Enhancing digestion and immunity in aquatic animals

After colonizing the gut, it:

• regulates microbial balance

• improves feed utilization

• boosts immunity

resulting in better growth performance and higher survival rates.

4. Reducing costs and increasing economic benefits

By lowering disease risks and improving survival and growth, overall farming efficiency is significantly improved.

4. Application Methods and Suggested Dosage

1. Water treatment

• Apply once every 7–10 days

• Standard dosage: 100–200 g per acre-meter

• Activation before use is recommended

2. Feed mixing

• Add 1–3 g per kg of feed

• Can be combined with molasses or vitamin C for enhanced results

3. Precautions

• Do not use simultaneously with disinfectants or antibiotics

• Ensure full dissolution or activation before application

5. Conclusion

      Bacillus subtilis plays a vital role in improving water quality, enhancing immunity, and promoting healthy aquaculture. As ecological farming continues to grow, this probiotic will remain one of the most valuable microbial tools for sustainable aquaculture development.