All creatures on the ground need water to survive. But have you ever wondered, do organisms living in a water environment need to drink water to sustain life like us?
Defining the feeling of “thirst”
What is thirst? This question is interesting because it relates to the term “thirst” – the feeling that we often understand as the urge to drink. Each person expressed this desire to a different degree. Motivation to drink water is how we ensure the balance of water and salt in the body.
Not only humans, but all terrestrial animals, face the risk of dehydration, and need to be replenished with enough water at all times. In other words, these animals drink water when they feel thirsty.
Do animals living in water environment need to be rehydrated?
Thirst is a completely different concept for aquatic organisms. Think about it: how do we get cravings if we live in a pizza? Likewise, how can fish be thirsty when they live in water all their lives?
However, this is not as simple as that. Fish still drink water. But freshwater fish and seawater behave differently to replenish water. This is related to their body composition.
Fish that is, fish that live in fresh water, do not have as high a salt content as seawater. They have a higher concentration of salt in their blood than in the freshwater in which they live. Therefore, the blood of freshwater fishes is at high risk of being diluted if they drink water.
This is why they do not actively drink water to maintain the balance of salt and water in the body. Instead, they absorb water through the skin and carry it by osmosis, and then urinate to remove all excess water.
Still saltwater fish so what?
Because the concentration of salt in the blood is lower than seawater – the habitat of saltwater fish (because seawater has a high salt content), their bodies are susceptible to dehydration, so they actively drink water.
The gill structure of saltwater fish is very special and is born to adapt to the environment so they can drink saltwater, treat it and then remove excess salt through excretion.
In the end, do fish really feel thirsty?
Fish actively drink water, yes, but is it because they are thirsty? The answer is no.
There are two reasons behind this. First, unlike mammals that are constantly looking for water to retain water, fish basically live in water, so their bodies have no urgent need to drink.
Another reason is that the feeling of thirst – for fish – is a reflex that occurs without the urge to be driven by the brain. It just happened instinctively. They don’t have to feel thirsty to drink water.
Isn’t that a very good thing? At least they won’t feel thirsty on a hot day, or after exercising like humans. The fish is so relaxed!