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Excretory Anatomy
Urinary Bladder
Vesica urinaria
A collecting sac downstream of the kidneys where urine accumulates before release - present in most bony fish, absent in cartilaginous fish.
Region: Trunk Universal in fish Unique to: bony
📖 Overview
Fish urinary bladders serve as reservoirs but also participate in ion reabsorption - actively pulling sodium and chloride back into the blood to conserve salts in freshwater fish.
🧬 Structure
Thin-walled sac connecting the paired kidneys via ureters to the urogenital pore. Wall contains smooth muscle for controlled voiding.
⚙️ Function
Urine storage, ion reabsorption (especially in freshwater species), and controlled release.
✨ Fun Fact
Freshwater fish urine is more dilute than their blood - the kidneys pump water out constantly to counter osmotic influx across the gills.
🔗 Related Excretory Structures