Nile tilapia (Oreochromis niloticus) is a global success story in aquaculture, ranking third in global freshwater fish production. Genetically Improved Farmed Tilapia (GIFT) is a particularly robust strain known for its rapid growth and adaptability. However, disease outbreaks can devastate tilapia farms and cause significant economic losses.
In this context, researchers from the International Centre of Insect Physiology and Ecology (Kenya), Maseno University (Kenya), and Tamil Nadu Dr. J. Jayalalithaa Fisheries University (India) characterized polyhydroxybutyrate (PHB)-producing bacteria from GIFT tilapia culture water in biofloc ponds and investigated the influence of PHB on the growth and immune performance of GIFT tilapia.
It is important to note that other researchers have used synthetic PHB as a carbon source for the biofloc system to improve nitrogen removal.
Biofloc: PHB-producing bacteria
Biofloc technology creates a unique aquaculture system. It minimizes water exchange and encourages a natural ecosystem within tanks. This ecosystem is teeming with beneficial bacteria, algae, and other microorganisms. These bioflocs not only improve water quality but also provide surprising benefits for fish.
One of the hidden gems within bioflocs is a group of bacteria with the remarkable ability to produce a compound called polyhydroxybutyrate (PHB).
PHB offers numerous benefits for tilapia aquaculture:
- Disease prevention: Studies have shown that supplementing fish feed with PHB can protect against various pathogens such as the Vibrio bacteria.
- Better growth and survival: Research suggests that supplementing with PHB can improve growth and survival rates in several fish species, including tilapia.
The present study: Unveiling the potential of PHB
This particular study aimed to investigate the presence and impact of PHB-producing bacteria within biofloc systems in GIFT tilapia. Here’s a breakdown of the research:
- Isolation and characterization: Scientists isolated and identified bacteria from biofloc water capable of producing PHB.
- Dietary supplement: GIFT tilapia were fed diets containing purified PHB extracted from these bacteria.
- Effects assessment: Researchers then compared the growth, immune response, and disease resistance of fish fed PHB with a control group.
Polyhydroxybutyrate extraction and improved growth
The study focused on biofloc pond, a type of aquaculture system that promotes the growth of beneficial bacteria alongside tilapia.
From water samples, researchers isolated and examined forty different bacterial strains. Six of these strains, including familiar names like Bacillus subtilis and Bacillus megaterium, showed the ability to produce PHB.
The PHB yield of these bacteria was impressive, ranging from 5% to a whopping 95.45% of their cell weight. The PHB champion producer? A strain of bacteria called Klebsiella pneumoniae.
But the benefits go further.
When PHB extracted from Klebsiella pneumoniae and Enterococcus hirae was incorporated into tilapia diets, the results were even more promising.
Fish fed a diet supplemented with PHB (5 g/kg) showed significantly better growth performance compared to the control group. They had higher weight gain, better feed conversion ratio (FCR), indicating better nutrient utilization, and a specific growth rate (SGR) that translates to overall faster growth.
Enhanced immune response: fighting diseases
The study also revealed a fascinating link between PHB and fish immune systems. Fish fed a diet supplemented with PHB showed a stronger immune response. They had elevated levels of serum protein, enzymes like myeloperoxidase and catalase, and improved antioxidant activity like superoxide dismutase. All these factors contribute to a stronger defense system against pathogens.
While both sources of PHB improved immunity, the group fed PHB from Klebsiella pneumoniae showed the most significant improvement. This translated into better survival rates when challenged with Aeromonas hydrophila bacteria, a common pathogen in aquaculture.
Benefits for tilapia aquaculture
When researchers supplemented tilapia feed with PHB extracted from biofloc bacteria, they observed interesting results. Fish fed PHB exhibited:
- Improved growth: Faster weight gain and better feed conversion rates.
- Greater disease resistance: Significantly lower mortality rates when exposed to pathogens.
Conclusion
“The results of the current study confirm the presence of PHB-producing bacteria in biofloc culture water. The PHB content extracted per dry weight of cells revealed bacterial behavior in the order of Klebsiella pneumoniae > Enteroccoccus hirae > Bacillus infantis > Bacillus megaterium > Exiguobacterium profundum > Bacillus subtilis,” conclude the researchers.
This study presents a double gain for sustainable aquaculture. It paves the way to use biofloc systems to produce valuable compounds like PHB. Furthermore, by incorporating PHB into fish diets, researchers have identified a potential strategy to promote healthy growth and disease resistance in tilapia.
The study was funded by the Department of Biotechnology located in New Delhi (India).
Contact
J. Mboya
Department of 7 Animal and Fisheries Sciences, Maseno University, Maseno, Kenya
P.O. Box Private Bag, Maseno, Kenya
Email: jimmybrianmboya@gmail.com
Reference (open access)
Meenakshisundaram, Menaga and Mboya, Jimmy and Sugantham, Felix, Polyhydroxybutyrate (Phb) from Biofloc Systems Enhances the Growth and Immune Performance of Genetically Improved Farmed Tilapia (Gift). Available at SSRN: https://ssrn.com/abstract=4783728 or http://dx.doi.org/10.2139/ssrn.4783728
