15 of the Largest Fish in Oceans, Lakes and Rivers

1. Whale Shark (Rhincodon typus)

The whale shark holds the title of the largest fish in the ocean. These gentle giants can reach up to 60 feet (18.3 meters) in length and weigh as much as 20 tons (18.1 metric tonnes). Despite their enormous size, whale sharks are filter feeders, primarily consuming plankton and small fish.

Found in tropical waters across the world's oceans, whale sharks are a key species for marine ecosystems but are currently classified as a threatened species, due to fishing pressures and habitat loss. Conservation efforts by organizations like the World Wildlife Fund are crucial for their protection.

2. Basking Shark (Cetorhinus maximus)

The basking shark is the second-largest fish species and can grow up to 40 feet (12.2 meters) long. Like the whale shark, basking sharks are filter feeders, using their gill rakers to filter plankton from the water. They are widely distributed in temperate oceans and are often seen near the surface.

Despite their impressive size, basking sharks face threats from fishing and entanglement in fishing gear, which has led to declining populations in some areas.

3. Great White Shark (Carcharodon carcharias)

Known for its power and formidable presence, the great white shark is one of the most famous sharks in the ocean. It can grow up to 20 feet (6.1 meters) in length, although some reports suggest larger individuals.

Great white sharks are apex predators with few natural predators themselves. They are distributed across a range of marine environments, including temperate and subtropical waters. Conservation concerns for great white sharks include bycatch and illegal hunting.

4. Giant Oceanic Manta Ray (Mobula birostris)

The giant oceanic manta ray, the largest species of manta ray, can reach up to 23 feet (7 meters) across its wingspan. These majestic creatures glide through the world's oceans, feeding on plankton and small fish. They are found in tropical and subtropical waters and are known for their complex behaviors and social interactions.

However, giant manta rays are threatened by fishing, particularly for their gill rakers, which are used in traditional medicine.

5. Tiger Shark (Galeocerdo cuvier)

The tiger shark is one of the largest shark species, reaching lengths of up to 18 feet (5.5 meters). Named for its striped pattern, which resembles a tiger's, this species is known for its diverse diet, which includes fish, squid and even marine mammals.

Tiger sharks are found in tropical and subtropical waters around the world and are adaptable to various marine environments. Though they are not currently classified as endangered, they face threats from commercial fishing and habitat degradation.

Honorable Mentions

The ocean is home to many remarkable creatures, each playing a vital role in their ecosystems. Protecting these giants, through sustainable practices and conservation efforts by organizations like the World Wildlife Fund, is crucial for maintaining the health of our world’s oceans.

1. Beluga Sturgeon (Huso huso)

Although primarily known for its presence in the Caspian and Black Seas, the beluga sturgeon can also be found in freshwater lakes and rivers. This species is the largest freshwater fish and can grow up to 23 feet (7 meters) long and weigh as much as 3,463 pounds (1,570.8 kg).

The beluga sturgeon is a true freshwater giant and holds the record for the maximum mass among lake fish. Unfortunately, Beluga sturgeons are heavily exploited for their caviar, a luxury item that has led to severe overfishing and poaching. The high demand for beluga caviar has driven illegal fishing practices, which, coupled with unregulated commercial fishing, has drastically reduced their populations.

Beluga sturgeons are notable for their late maturation and long lifespan. They can live for up to 100 years and only reach sexual maturity between 15 to 20 years of age. These fish undertake significant migrations from the sea to freshwater rivers to spawn.

During their spawning migrations, they travel upstream to lay eggs, a journey that is critical for their reproduction but also exposes them to additional threats from habitat disruption and barriers.

Conservation efforts are crucial for the survival of the beluga sturgeon. Protecting their habitat, enforcing fishing regulations and combating poaching are essential steps in preserving this ancient fish.

2. Alligator Gar (Atractosteus spatula)

Native to North America, the alligator gar is one of the biggest fish species found in freshwater lakes and rivers. It can reach lengths of up to 10 feet (3.1 meters) and weigh around 300 pounds (136.1 kg). Known for its prehistoric appearance and formidable size, the alligator gar is a top predator in its environment.

Despite its impressive size, this fish faces threats from habitat destruction and overfishing, particularly in the Lone Star State of Texas.

3. Lake Sturgeon (Acipenser fulvescens)

The lake sturgeon is a prominent species in the Great Lakes and other North American freshwater bodies. These ancient fish can grow up to 8 feet (2.4 meters) long and weigh up to 200 pounds (90.7 kg).

Known for their distinctive armor-like scales and long lifespan, lake sturgeons are an important part of their ecosystems. They face threats from fishing, which have significantly impacted their populations.

4. Lake Trout (Salvelinus namaycush)

Found in the cold, clear waters of North America's Great Lakes and northern lakes, the lake trout is a sizable freshwater fish that can grow up to 40 inches (1 meter) long and weigh up to 60 pounds (27.2 kg).

Lake trout are prized by anglers for their size and challenging catch. They are an important species in their habitats but are vulnerable to overfishing and ecological changes, which can affect their populations.

5. Largemouth Bass (Micropterus salmoides)

While not as massive as some other species on this list, the largemouth bass is one of the most popular game fish in North America. It can reach a maximum length of 30 inches long and weigh up to 12 pounds (5.4 kg), with some exceptional catches reported to be even larger.

Known for its aggressive behavior and, well, large mouth, the largemouth bass is a favorite among anglers and plays a significant role in freshwater sport fishing.

Honorable Mentions

These colossal lake fish represent some of the largest freshwater giants, each playing a vital role in their ecosystems. They are often subjects of record-setting catches and symbolize the grandeur of freshwater habitats.

However, many of these species face challenges from fishing and habitat loss, emphasizing the need for ongoing conservation efforts to protect these remarkable creatures and their environments.

Freshwater fish species, like those from the catfish or sturgeon family, may not have the luxury of expansive habitats like their ocean- and lake-dwelling counterparts, but they thrive in wide, slow-moving rivers.

1. Mekong Giant Catfish (Pangasianodon gigas)

The Mekong giant catfish holds the title for the largest freshwater fish in Southeast Asia's Mekong River, which flows through China, Myanmar, Lao PDR, Thailand, Cambodia and Vietnam.

This colossal fish can reach a maximum length of 10 feet and weigh as much as 660 pounds (299.4 kg). Known for their large size and unique appearance, Mekong giant catfish are filter feeders, consuming small organisms found in the river.

They are critically endangered, facing threats from overfishing and habitat destruction. Conservation efforts are crucial for this species, as they are an important part of the river's ecosystem.

2. Chinese Paddlefish (Psephurus gladius)

Once a prominent inhabitant of the Yangtze River in China, the Chinese paddlefish was one of the largest freshwater fish, capable of reaching lengths of up to 23 feet (7 meters). It had a distinctive long, paddle-shaped snout and primarily fed on other fish.

Sadly, this species is now considered functionally extinct in Central Asia, with the last confirmed sightings being in the early 2000s. The decline of the Chinese paddlefish serves as a stark reminder of the impacts of habitat loss and pollution on freshwater species.

3. White Sturgeon (Acipenser transmontanus)

The white sturgeon is one of the largest sturgeon species and can be found in rivers along the west coast of North America, such as the Columbia and Fraser Rivers. These ancient fish can grow up to 20 feet (6.1 meters) long and weigh over 1,500 pounds (680 kg).

Known for their bony, armor-like scales and sharp teeth, white sturgeon are apex predators in their habitats. Despite their impressive size, they are facing threats from habitat loss and overfishing, making conservation efforts essential.

4. Giant Barb (Catlocarpio siamensis)

The giant barb is a massive fish species found in the river systems of Southeast Asia, particularly in Thailand and Cambodia. It can reach lengths of up to 9 feet (2.7 meters) and weigh around 550 pounds (249.5 kg). The giant barb is known for its robust size and the ability to consume a variety of other fish.

Unfortunately, this species is also threatened by habitat loss and overfishing, highlighting the need for effective conservation measures to protect these giants.

5. Arapaima (Arapaima gigas)

Native to the Amazon Basin in South America, the arapaima is one of the largest fish in the world and can grow up to 10 feet (3.1 meters) long and weigh up to 485 pounds (220 kg). Known for its large size and impressive scales, the arapaima primarily feeds on smaller fish and aquatic organisms.

This species is of significant importance to the local fisheries and has faced pressures from overfishing and habitat degradation. Efforts are underway to ensure the sustainability of arapaima populations in their natural habitats.

Honorable Mentions

These massive river fish represent some of the biggest species in freshwater environments. Their impressive sizes and vital roles in their ecosystems make them key indicators of river health. However, many of these fish are now threatened due to habitat loss, overfishing and other environmental pressures.

Protecting these giants is essential for maintaining the biodiversity and ecological balance of our world's freshwater systems.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.