When it comes to the world of aquatic life, Mozambique tilapia are remarkably tolerant to salt water.
They survive in habitats ranging from fresh water to hypersaline ponds that are three times saltier than the ocean, and researchers at University of Hawaiʻi at Mānoa’s College of Tropical Agriculture and Human Resilience now unlocked one of the molecular mechanisms underlying this remarkable feat.
A new study published in General and Comparative Endocrinology was led by researcher and professor Andre Seale in College of Tropical Agriculture and Human Resilience Department of Human Nutrition, Food and Animal Sciences, alongside student researchers.
The team discovered how the tilapia survive under extreme salt stress by gradually increasing tank water salinity with artificial sea salt.
Several fish species, including tilapia, need the hormone prolactin to prevent excessive water uptake and ion loss in fresh water — and turn it down when entering salt water. However, in extreme hypersalinity, prolactin signaling continues to be suppressed while a continuous shift happens in the types of prolactin genes being expressed.
This allows the fish to fine-tune their ability to regulate salt and water balance even during transitions into salty environments.
“This salinity acclimation capacity is gradual, and even this species will fail to survive a direct transfer from fresh water to seawater,” said Seale. “Understanding the rate and limits of how these fish tolerate higher salinities also helps improve production traits, including growth, feed efficiency and nutritional value.”
Tilapia is a staple of global aquaculture and local Hawaiian aquaponics.
Understanding the mechanisms underlying salt tolerance enables farming in brackish water, preserving precious freshwater for agriculture and drinking. It also allows for investigation of how salt water could affect the nutritional quality of the fish.
This research could even play a role in boosting fish production and quality in regions with limited freshwater supply.
