Osmoregulation is the maintenance of constant osmotic condition to regulate the water content and solute concentration in body.

# 1. Osmoregulation in bony fishes (freshwater) :

The fresh water bony fishes have gills and kidney for the osmoregulation. The fishes have gills and kidney for the osmoregulation. The fishes have hypertonic body fluids. Therefore there is a constant loss of ions from body. It balances the volume of water and salts by three means;
- i.Produce large amount of glomerular filtrate.
- ii.The large amount of selectively reabsorbed solute passes through the renal tube so fish excrete hypotonic urine.
- iii.Freshwater fish can take up Sodium ion and Chlorine ion from water directly due to the patience of Ionocytes cells in their gills.

# 2. Osmoregulation in marine bony fishes :

The fishes have hypotonic body fluid. There is constant loss of water from body. Marine fish conserve the water and loss ion to overcome dehydration of tissue by following ways :
- i. It constantly drinks sea water. Kidney lack of glomeruli so nitrogenous wastages are secreted directly into renal tubules and water is absorbed by osmosis.
- ii. Ionocytes help to expel monovalent anions from body fluids to seawater and divalent cations from faeces.

# 3. Osmoregulation in human :

In case of human hypertonic urine is excreted. This minimizes the water loss from their body. The filtrate fluid in Bowman's capsule (isotonic) passes through the tubules of nephrones. Then a large amount of water and solutes are reabsorbed during this course.

During cold month, hypotonic urine is excreted but in warmer month hypertonic urine is excreted due to sweating.