How Salty?

Aquaculture researcher Andre Seale is lead author on a new publication, “Systemic Versus Tissue-Level Prolactin Signaling in a Teleost During a Tidal Cycle.” As the abstract explains, Mozambique tilapia (Oreochromis mossambicus) are native to estuaries where they encounter tidal fluctuations in water salinity. These fluctuations can be dramatic, subjecting the fish to salinities characteristic of both fresh water and seawater within a single tidal cycle. 

For their study, the co-authors reared tilapia under a tidal regimen that simulated the dynamic conditions of their native habitat. Then they sampled different indicators every three hours to track how the signaling of prolactin, a hormone that helps fish regulate osmotic pressure in their bodies, is modulated in parallel with genes encoding branchial effectors. Throughout the 24-hour sampling period, plasma osmolality reflected whether tilapia were sampled during the fresh water or salt water phases of the tidal cycle, whereas pituitary prl gene expression and plasma prolactin levels remained stable. 

Indications were that fish exposed to tidally changing salinities regulate the expression of certain gene transcripts in a similar fashion as fish held under static salt water conditions. The authors conclude that it’s the local (branchial) regulation of endocrine signaling that underlies the capacity of euryhaline fishes like Mozambique tilapia to thrive under dynamic salinity conditions.