Salinity adaptation in fish: effect of thyroxine on mitochondrial status

Area of Science:

• Physiology
• Biochemistry
• Environmental Science

Background:

• Freshwater fish (Sarotherodon mossambicus) face physiological challenges when transferred to saline environments.
• Gill mitochondria are crucial for energy metabolism and ion regulation, and are likely affected by osmotic stress.

Purpose of the Study:

• To investigate the functional changes in gill mitochondria of Sarotherodon mossambicus upon transfer to 50% seawater.
• To determine the effect of thyroxine administration on these stress-induced mitochondrial alterations.

Main Methods:

• Monitoring key mitochondrial functions including ADP/O ratio, respiratory control index (RCI), ATP-Mg2+ induced contraction, and energy-dependent 45Ca uptake.
• Assessing amino acid incorporation capacity, adenine nucleotide content, and endogenous Ca2+ levels.
• Administering thyroxine to stressed fish and evaluating the reversal of mitochondrial dysfunction.

Main Results:

• Transfer to 50% seawater caused loss of ADP/O and RCI, impaired ATP-Mg2+ induced contraction, and reduced energy-dependent 45Ca uptake.
• Increased amino acid incorporation, adenine nucleotide content, and endogenous Ca2+ were observed in mitochondria from fish in 50% seawater.
• Thyroxine administration effectively reversed these functional changes in gill mitochondria, with sustained effects.

Conclusions:

• Osmotic stress significantly disrupts gill mitochondrial function in Sarotherodon mossambicus.
• Thyroxine plays a vital role in restoring mitochondrial function under osmotic stress, potentially by promoting mitochondriogenesis.