Do fish drink water? Here's what scientists have to say

Produced by Tarun Mishra

Osmosis

Fish do not get thirsty in the same way humans do, but their bodies constantly interact with water through a process called osmosis. Water moves across a fish's cell membrane from areas of low solute concentration to areas of high solute concentration, aiming to balance the salt content inside the fish with that of its surroundings.

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Hydration Challenges

Saltwater fish face constant dehydration because seawater contains a much higher salt concentration than their bodies. This forces them to drink seawater constantly, but they must also work to expel the excess salt through specialised chloride cells in their gills.

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Salt Removal

To avoid the harmful effects of excess salt, saltwater fish use chloride cells to pump salt out of their bodies. Their kidneys also help by producing salty urine. To conserve water, these fish rarely urinate, and when they do, their urine is highly concentrated with salt.

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Freshwater Fish Face

Freshwater fish, on the other hand, face a different issue: water constantly flows into their bodies due to the lower concentration of salts in the water. They do not drink water purposefully but may take in small amounts incidentally while feeding. Their primary method of maintaining balance is through continuous urination.

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Freshwater Fish

Freshwater fish have chloride cells that work to pull salt into their bodies to counterbalance the incoming water. This process requires energy, as the fish must actively remove the excess water while retaining necessary salts.

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Regulation Mechanism

Sharks operate under a different system altogether. Instead of drinking water directly, sharks maintain high levels of urea in their bodies, balancing their internal salt concentration to match the surrounding seawater. Excess salt is expelled through chloride cells at a gland in their rectum.

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Constant Challenge

Whether in salty or fresh environments, the key challenge for fish is maintaining the right balance of salts and water. While their methods differ, all fish must adapt to the constant flow of water across their bodies to stay hydrated and function properly in their ecosystems.

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