Water covers around 70% of the earth’s surface. It is no surprise that thousands of different animal species inhabit these waters.
Over the years and to date, there have been records documenting the existence and features of various water creatures.
Although many of them are now extinct, many that still exist evolved. Fish are the most prevalent aquatic animals and come in various species and types.
They are generally classified according to habitat, dentition, appearance, diet, whether or not humans can consume them, etc.
Based on their habitat, they are primarily classified into salt and freshwater fish.
In this article, you will learn the differences between salt and freshwater fish and discover the biggest salt and freshwater species in the United States.
What is the Biggest Saltwater Fish in the USA?
The whale shark, Rhincodon typus, is the largest saltwater fish in the United States.
Whale sharks live in tropical oceans, but are present in many other saltwater settings.
They can also live in other parts of the world, including in the western Atlantic Ocean off the United States city of New York.
Despite their name, whale sharks are fish and not whales; their size inspires their name.
Apart from being the largest saltwater fish in the United States, whale sharks are also the biggest fish in the United States and the world.
These giants weigh between 15 and 21.5 tonnes (30,000 to 43,000 lbs). They can also grow up to 60 feet long, but they usually average around 41 feet.
The largest whale shark ever found and recorded weighed around 60 tons and reached a length of 62 feet.
Although they are widespread in several areas of the world, the International Union for the Conservation of Nature (IUCN) categorized them as endangered, meaning they face a high risk of going extinct in the wild.
Whale sharks usually swim toward the surface of oceans, and despite their enormous size, they are mostly docile animals that enjoy human company.
However, exercising caution around these giants is still necessary, considering they can kill humans without doing too much.
The easiest way to spot and identify whale sharks is by the different spots and patterns found on their skin. Like human fingerprints, every whale shark has a distinctive pattern of spots and stripes.
When they migrate through tropical waters, these patterns assist scientists in tracking their movements.
Whale sharks have pale undersides and dark tops, with several bright spots or stripes covering the dark regions of their body, and have mouths in front of their broad, flat heads.
Because of their dark top halves, whale sharks can easily swim around undetected.
What is the Biggest Freshwater Fish in the USA?
The biggest freshwater fish in the United States is the white sturgeon.
Compared to the smallest freshwater fish ever recorded, around a maximum standard length of 10.3 mm, the white sturgeon usually reaches 14 feet long and weighs between 900 and 1,500 pounds.
The longest white sturgeon recorded was over 20 feet long, while the largest weighed over 1,800 pounds.
The white sturgeon is common in several parts of North America, including the United States, and it lives in areas such as California, Oregon, and Washington.
Despite what their name suggests, white sturgeon are not mostly white. Instead, their dorsal (upper body) region is grayish or brownish, while their ventral (underside) section is white.
Although having a shark-like appearance, this fish is not closely related to sharks.
The appearance of a heterocercal tail fuels this misconception. Despite having a big mouth, it lacks teeth and instead captures prey through suction.
White sturgeon possess rows of four to eight scutes rather than scales (bony plates). They can also easily detect aquatic prey because of the four barbels surrounding their mouths.
Unlike sharks, which white sturgeon share a resemblance with, white sturgeon are not particularly dangerous.
They are primarily considered scary because of their huge size. Beyond this, they are considered gentle towards humans and other animals, and the only time they would ever attack is if they feel threatened or cornered.
What Are the Primary Differences Between Salt and Freshwater Fish?
The primary distinction between salt and freshwater fish is their habitat; the former resides in saltwater, while the latter resides in freshwater.
Saltwater fish naturally adapt to the sea and other saline bodies of water, and they are also called marine fish or sea fish. Saltwater fish come in diverse colors, sizes, and shapes.
An estimated 20,000 species of saltwater fish are found worldwide, meaning the majority (around 58%) of all known fish are saltwater fish.
Saltwater fish lose a significant amount of water through their gills via osmosis. As a result, saltwater fish consume a large amount of saltwater to help replace the loss they constantly experience through their gills.
While saltwater fish have to balance the amount of water in their bodies, their freshwater counterparts are more focused on maintaining their salt levels in an environment with little to no salt.
They have thick, sturdy scales covering their entire body and regulating their osmotic balance.
Freshwater fish can also preserve salt while forcing water through their gills. These gills distribute water, keeping contaminants out while preserving the fish’s internal organs.
Freshwater fish also have huge, well-developed kidneys that can process a lot of water. Their kidneys also help them maintain the amount of salt present in their blood.
Freshwater fish may be more resilient and able to adapt to constantly changing environments more readily than saltwater fish.
This is why it is more common to find freshwater fish in aquariums compared to their saltwater counterparts.
This diversity helps them survive various habitat types; rivers, lakes, ponds, etc.
These freshwater fish can also withstand various temperatures; some species can flourish in regions between five and 15 degrees Celsius, while others can only tolerate mild temperatures of around 24 degrees Celsius.
Saltwater fish, on the other hand, thrive in more stable environments. These fish swim worldwide, from the warmer tropical seas to the icy Antarctic and Arctic oceans.
Another difference between salt and freshwater fish is their size. Over the years, it has been discovered that saltwater fish are usually larger than their freshwater counterparts.
This is because they have more conditions to grow and survive. The high salt concentration in saltwater habitats helps these fish float, meaning they do not struggle to move against any current.
As previously established, freshwater habitats have less saline content than saltwater habitats.
As such, freshwater fish are leaner than their saltwater counterparts because they struggle to swim against the current.
Another reason for their naturally lean structure is that these freshwater fish enjoy migrating from their primary habitat when their breeding season is near.
On the other hand, saltwater fish are rounder than their freshwater counterparts.
What Fish Can Survive in Salt and Freshwater Habitats?
Despite having different habitats depending on several reasons, all fish must have a certain salinity level in their blood.
As established earlier, freshwater fish must maintain their saline levels in their habitats because many freshwater habitats have a salt level of around 0.05%.
In contrast, saltwater fish must work to keep excess salt out of their bodies.
The process these fish go through to reach and manage the optimum saline level is called osmoregulation.
Fish that can survive in habitats of varying salinity levels are called euryhaline fish.
Fish under this category do so because their lifecycle requires them to migrate between salt and freshwater habitats. As such, they naturally develop the ability to survive in both habitat types.
How well a fish can osmoregulate and keep a balance between freshwater and saltwater determines how well it can endure varied salinities. One of the most common fish that can achieve this balance is salmon.
Although salmon lay their eggs at the upper levels of (freshwater) streams, they spend most of their lives in the open ocean, where they reach sexual maturity.
Young salmon spend several months traveling downstream to the ocean after hatching from the eggs before staying there for three to five years.
The adult salmon then migrate upstream to the freshwater’s headwaters when they reach maturity, reproduce, and then die.
Other fish that can achieve this feat include puffer fish, lamprey, tilapia, and trout.
In contrast to euryhaline species, stenohaline ones can only endure within a constrained range of salinities.
Since most freshwater and saltwater fishes are stenohaline, they cannot survive in habitats that go against their bodily structures.
For saltwater fish, saltwater is hypertonic, which means that water is constantly lost through the skin.
To counter this, these marine fish consume more water and use their gills and kidneys to filter out extra salt.
Similarly, freshwater fish are hypotonic, meaning water is being forced into the skin, and these fish urinate more frequently to combat this.
Because of these differences, fish can’t simply move between different salinities due to these variations between freshwater and saltwater species.
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