Nile tilapia is essential for global food security, but live transport often induces stress. This stress disrupts their internal balance and weakens their skin, a vital barrier against diseases and injuries. Imagine their scales becoming thinner, mucus production decreasing, and pigment distribution changing: all signs of a stressed and vulnerable fish.
A study conducted by a team of scientists from the Animal Health Research Institute (ARC) and Sohag University investigated the histopathological responses of the skin of Oreochromis niloticus attributed to stress and salt addition during transportation.
Stress Science and Skin
Stress, as defined by Schulte (2014), is an imbalance caused by external factors. Fish react by adjusting internal processes to maintain balance. Understanding these responses is crucial for optimizing aquaculture practices and ensuring fish welfare.
Fish skin, equipped with scales and mucus, acts as a shield against environmental threats. However, handling, physical trauma, and stress can damage this delicate barrier, making fish more susceptible to diseases. Particularly, the skin is also equipped with a “mucosal immune system” (SALT) that helps combat pathogens.
The Stressful Journey of Fish
Transporting live fish can be challenging for them. Crowded tanks, bumps, and changing water conditions create stress, leading to skin damage. This not only harms fish welfare but also affects their marketability.
Various studies describe the physiological responses of fish to stress regarding endocrine systems, osmoregulation, respiration, and behavior. Furthermore, it is well-known that the immune response is suppressed in stressed fish.
Salt to the Rescue?
A key solution to mitigate stress and protect the skin during transportation is salt (NaCl). Adding salt to transport water is a simple and affordable practice commonly used in freshwater fishing facilities.
Scientists evaluated changes in skin morphology and epithelial barrier integrity of tilapia after 5-hour transportation in saltwater (0.5%) and freshwater.
The study compared three groups of tilapia:
- Control: Not transported
- Transported without salt: Exposed to transportation stress
- Transported with salt: 5 grams of salt per liter of water added.
Looking beneath the Skin
Researchers examined fish skin under a microscope and revealed:
- Transported without salt: Damaged skin, thinner epidermis (outer layer), fewer mucus-producing cells, and pigment changes.
- Transported with salt: Milder cutaneous changes, normal mucosal cell density, and mostly normal pigment distribution.
The Verdict: Salt Wins!
Adding salt significantly improved the skin health of transported fish compared to those without salt. They had:
- Preservation of skin thickness and mucus production: Salt helps maintain the natural protective barrier, crucial for osmoregulation and defense against pathogens.
- Improved pigment distribution: Balanced pigment distribution indicates reduced stress and healthier skin.
- Microscopic confirmation: Images show smoother skin surfaces with open mucous cells in salt-treated fish, indicating better protection.
This suggests that salt helps protect the skin and reduce stress during transportation.
Why Salt Works
Salt likely helps in two ways:
- Reducing water loss: Fish naturally lose water through their gills. Salt helps maintain internal water balance, reducing stress and potential skin damage.
- Protecting mucosal layer: Skin mucus acts as a barrier against pathogens and irritation. Salt may help maintain this layer intact, further protecting the fish.
Application in Tilapia Aquaculture
By protecting the skin, salt indirectly favors:
- Better fish welfare: Reduced stress and healthier skin lead to better survival and growth.
- Enhanced disease resistance: Healthy skin acts as a stronger barrier against pathogens.
- Higher-quality fish: Healthier fish translates to better appearance and potentially tastier meat.
Conclusion
According to the study results, salt plays a significant role in protecting Nile tilapia skin during transportation, improving fish welfare, disease resistance, and overall quality.
The study highlights the importance of considering fish welfare during transportation. Adding salt to water emerges as a simple yet effective way to reduce stress and protect Nile tilapia skin, ultimately benefiting both fish and the aquaculture industry. This study adds to the research conducted on salt use in tilapia transportation.
Share this information with fish farmers to raise awareness about the benefits of salt in fish transportation.
Funding for the study was provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).
Contact
Fatma Abo Zakaib Ali
Pathology and Clinical Pathology Department, Faculty of Veterinary Medicine, Sohag University
Sohag, 82524, Egypt
Email: fatma_ali@vet.sohag.edu.eg
Reference (open access)
Hana, H.N.S., El-Lateif, R.S.A.A., El-Galil, M.A.E.A.A.A. et al. Skin histopathological responses of Oreochromis niloticus (Nile tilapia) to transportation in water with and without salt. BMC Vet Res 20, 55 (2024). https://doi.org/10.1186/s12917-024-03899-y
