Most saltwater fish have to drink the water around them. The aquatic environments of these fish contain high levels of dissolved salt. The higher salinity causes the water from the bodies of these fish to flow out through their gills. So saltwater fish need to drink water constantly to stay hydrated.
Let’s understand in more detail why saltwater fish drink salty water.
2 Reasons Saltwater Fish Drink Water
Like other creatures, saltwater fish species need water to support the chemical reactions that take place within them.
Without drinking water, these fish won’t have any solvent in them, which could be fatal.
Given below are a few reasons why saltwater fish drink water.
1. Restore Water Loss
Saltwater fish have a lower salt concentration inside their bodies than the saltwater they inhabit.
This results in osmosis, a process that removes water from their bodies and expels it into the sea.
This continuous and free diffusion of water through the gills shrivels up the fish.
So the saltwater fish must replenish the water lost through the osmosis process.
2. Maintain Optimal Fluid Balance
In a saltwater environment, fish experience more salt and less water around them.
As a result, their bodies take on salt and lose water to the sea.
Marine fish need to drink large quantities of water and urinate less to combat this problem.
In addition, their body absorbs only water and eliminates salt to maintain the required fluid balance.
Do Saltwater Fish Feel Thirsty?
Saltwater fish don’t feel thirsty. However, they need to drink water to restore the constant fluid loss from their bodies. Without drinking water, the chances of dehydration are very high, which can be fatal for saltwater fish.
Different types of fish species inhabit the seas and oceans.
And their analogical and physiological differences make them behave differently in their aquatic environment.
So let’s understand how different types of fish satiate their water requirements.
1. Bony Fish
Marine bony fish like the grunts, herring, tuna, etc., are hypertonic to seawater.
Therefore, they continuously lose water from their bodies through osmosis.
Osmosis is a process by which water moves through a semi-permeable membrane (fish’s skin) from areas of low solute concentration to high solute concentration.
The body of a bony fish is less salty than the seawater it inhabits.
As a result, due to osmosis, water moves out from the fish’s body into the sea through its skin and gills.
The persistent water loss from the body can be fatal for the fish.
So bony fish have to drink water constantly to keep their bodies hydrated. Hence, they never actually feel thirsty.
2. Cartilaginous Fish
The cartilaginous fish, like sharks and rays, are isotonic to the seawater they inhabit.
Their bodies have the same salt concentration as that of seawater.
Cartilaginous fish also don’t lose water continuously from their bodies like bony fish.
However, they do absorb a tiny amount of water through their gills due to osmosis.
They also excrete or remove excess salt from their bodies to maintain the required level.
So these fish species don’t drink water directly as they never feel thirsty.
3. Migratory Fish
Migratory fish like salmon and others are born in freshwater, and they then move to the sea.
Moreover, they return to the freshwaters to spawn.
These fish have highly sophisticated gill membranes that help them switch things depending on the freshwater or saltwater environment they inhabit.
These fish also lose water through the osmosis process in a saline environment.
That’s why they have to replenish the lost water to stay hydrated.
Okay! So it’s clear that saltwater fish don’t feel thirsty.
However, they must maintain adequate water levels inside their bodies to avoid dehydration.
How Do Saltwater Fish Drink Water or Keep Themselves Hydrated?
Saltwater causes marine fish to lose water continuously from their bodies, which can be fatal.
So marine fish hydrate their bodies by drinking water and removing excess salt.
Given below are the ways in which saltwater fish drink water to keep themselves hydrated.
1. Through Their Mouth
Saltwater fish must purposely drink water to maintain enough liquid in their bodies to avoid dehydration, which is caused due to osmosis.
Freshwater fish direct all the ingested water out of their bodies through their gills.
However, saltwater fish direct some amount of water that they ingest from their mouth into their digestive tract.
It helps the fish to replenish the water loss from their bodies that constantly happens through the osmosis process.
Fish use osmoregulation to efficiently handle the processes of diffusion and osmosis.
The osmoregulation process helps the fish maintain a balance of salt and water in their body, which is vital for their efficiency and survival.
In addition, marine fish kidneys eliminate excess salt by pumping it into their pee to throw it out of their body.
Their gills also have special cells that flush out excess salt into the sea.
Do All Saltwater Fish Drink Water?
All saltwater fish don’t need to drink water. Marine bony fish drink water to maintain optimal fluid balance and avoid dehydration. Conversely, cartilaginous fish don’t drink water directly as there is no water loss from their bodies.
The water inside the bodies of saltwater fish has a lower concentration of salt than saltwater.
As a result, water from less salty areas of the fish body moves out into the sea.
It leaves the saltwater fish dehydrated, so they drink or absorb water to rehydrate themselves.
The only exception is the cartilaginous fish like sharks, which are very different from bony fish.
Their bodies have very salty blood, which has the same salt content as the water they inhabit.
So sharks don’t need to drink water to keep their bodies balanced because they’re already well-hydrated.
However, a tiny amount of water can enter their bodies as they intake dissolved oxygen from the water.