What Happens to All the Water That Fishes and Other Sea Creatures Ingest When They Eat Something?

When fish and other sea creatures ingest food, they also take in water. But what happens to that water? This question arises naturally when we think about the aquatic counterparts munching on their prey. Just like we worry about swallowing air when eating under water, they must also manage the excess water they ingest. However, these creatures have evolved various mechanisms to handle this.

Key Mechanisms in Managing Ingested Water

Let's break down the different processes involved in managing this water:

Digestion

When fish and other marine animals ingest food, the water mixes with the food in the digestive system. This mixture aids in the enzymatic breakdown of nutrients such as proteins, fats, and carbohydrates. The water helps in the absorption of these essential nutrients.

Absorption

After digestion, nutrients and some of the water are absorbed through the walls of the intestines into the bloodstream. This process ensures that the animal can effectively utilize the water and nutrients.

Osmoregulation

Aquatic animals have specialized cells and structures to maintain fluid balance, a process known as osmoregulation. Different species adapt to their environments, absorbing more or less water accordingly:

Freshwater Fish: These fish tend to absorb more water through their skin and gills due to the lower concentration of salts in their environment compared to their bodily fluids. They excrete excess water through urine. Saltwater Fish: Saltwater fish lose water to their environment and must drink seawater to compensate. They actively excrete excess salts to maintain the appropriate balance of water and salinity in their bodies.

Excretion

Any excess water that is not needed for metabolic processes is excreted. This can happen through urine or gill excretion, depending on the species and environmental conditions.

Overall, the water ingested by aquatic animals plays a crucial role in digestion and maintaining their internal balance. They have evolved various methods to manage this water efficiently.

The Aquatic Dilemma

This seems like a natural question to ponder. After all, if you eat underwater, you’re bound to swallow a lot of water. And in the ocean, that will be saltwater, and that much salt can't be good, right? However, if you think about it, this might be like an aquatic creature wondering about what we do with all the air we must swallow when we eat something. That much air can't be good for us either!

Of course, we usually don't swallow an extraordinary amount of air when we eat because we have evolved to eat in a gaseous environment. Our swallow reflex automatically excludes most air from our food when we chew and swallow by squeezing it as it goes down our esophagus into our stomach. We do swallow a bit of air, but usually not enough to be problematic. If we do get too much, we have ways of expelling it.

Similarly, fish and sea creatures adapted to eat in a marine environment. They generally do not chew or masticate their food, so there is little mixing of their food with the water. When they swallow, most of the excess water is forced out through the mouth and gills, and the solid food moves into the stomach. Not much water is swallowed with it. If too much is swallowed, the fish can expel the excess through osmosis. Any surplus salt is likewise expelled to maintain the appropriate balance of water and salinity in their bodies.

Marine mammals and other creatures have similar ways of dealing with this. For example, marine iguanas expel surplus salt through their nostrils, and mammals like dolphins and whales excrete it in their urine.