These sustainable solutions to manage and mitigate columnaris disease in catfish were inspiring and motivating to the farmers.

The short-term feeding trial (60 days) was carried out in a recirculatory system with a low protein diet containing 28 percent protein where the main  protein sources were soybean and bone meal supplemented with either protease enzyme (175g per tonne) or humic substance (23g per tonne).

This was aimed at improving catfish growth and immunity and enhancing their resistance to columnaris disease. These regular diets were offered to the catfish fingerlings along with a control diet of low protein and a high protein with fishmeal.

The different dietary groups of catfish were challenged with Flavobacterium covae for 8 days after completion of the feeding trials.

The health indicators were studied from tissue samples from fish post-feeding and post challenge trials

Results:
1. Growth
• The inclusion of protease enzyme or humic substance after a 30- or 60-day feeding period did not affect the growth metrics.
• The high-protein dietary control groups showed general growth improvement.
• Better growth compared to the similar feed without additives was achieved by the low-protein supplemented feed.

2. Immunity
• Investigation of lysozyme activity in the blood showed that catfish fed either the protease or humic substance had improved innate immunity response in a response to the bacteria challenge activity.
• An increase in immune-related genes in the kidney of fish was also observed.

3. Resistance to columnaris disease
• Catfish survival was significantly improved in catfish fed either protease or humic substance, as the lowest mortality (~25 percent) was shown following F. covae infection.
• Mortality up to 45 percent in the low and high protein soy diet.

Conclusion:
• In the catfish group fed the control diets, mortality up to ~60 percent was demonstrated in the high protein fishmeal

• Humic substances and protein enzymes enhance catfish’s immune response to protect them against columnaris disease

• Columnaris disease can be a devastating pathogen for the catfish industry, particularly during seasonal temperature changes

• The study suggests that both the protease enzyme and humic substance could be applied to commercial catfish aquafeeds.

• They enhance the immune system and resistance to lethal bacterial infection and have no adverse effects on fish growth.

• They enhance the immune system and resistance to lethal bacterial infection and have no adverse effects on fish growth.

• It also suggests that low-protein soy diets containing proteases and humic substances should be considered better alternatives to high-protein diets that include fishmeal.

• Protease enzymes can break down complex amino acids and degrade anti-nutritional factors, which are prominent in soybeans.

• Furthermore, the study inferred that humic substances, although their application is new in fish, could stabilize intestinal microflora in catfish, thereby enhancing nutrient utilization in fish feed.

• At relatively low inclusion levels, these additives showed practical value as immunostimulants for catfish production which is very crucial in mitigating losses in the catfish industry

• Dietary stimulating alternatives remain one of the promising solutions for disease treatment and growth promotion.