Occludin expression in goldfish held in ion-poor water

Area of Science:

• Physiology
• Environmental Science
• Molecular Biology

Background:

• Goldfish (Carassius auratus) are often exposed to varying water ion concentrations.
• Understanding physiological and molecular responses to ion-poor water (IPW) is crucial for fish survival.
• The tight junction protein occludin's role in ionoregulation is not fully understood.

Purpose of the Study:

• To investigate goldfish responses to abrupt and long-term exposure to ion-poor water (IPW).
• To examine changes in serum parameters, Na(+)-K(+)-ATPase activity, and occludin expression in key ionoregulatory tissues.

Main Methods:

• Goldfish were exposed to IPW for abrupt (0-120 h) and long-term (14, 28 days) periods.
• Serum osmolality, [Na(+)], [Cl(-)], and glucose were measured.
• Na(+)-K(+)-ATPase activity and occludin expression in gill, kidney, and intestine tissues were analyzed.

Main Results:

• IPW exposure lowered serum osmolality, [Na(+)], and [Cl(-)], while increasing serum glucose.
• Abrupt IPW exposure decreased gill Na(+)-K(+)-ATPase activity and transiently increased occludin expression.
• Long-term IPW acclimation elevated gill occludin expression and, at day 14, Na(+)-K(+)-ATPase activity.
• Kidney Na(+)-K(+)-ATPase activity and occludin expression increased after 28 days in IPW.
• Intestinal occludin expression initially declined but returned to control levels by day 28.

Conclusions:

• Goldfish demonstrate tolerance to both acute and chronic IPW exposure.
• Occludin likely plays an adaptive role in modulating epithelial barrier properties in ionoregulatory tissues during acclimation to IPW.
• These findings provide insights into fish osmoregulation and adaptation mechanisms in challenging aquatic environments.