38 Fascinating Fun Facts About Fish

Fish are some of the most diverse and surprising animals on Earth. From the tiny darters of freshwater streams to the glowing giants of the deep sea, fish have evolved to survive—and thrive—in nearly every aquatic environment imaginable. Whether you’re teaching a science class, planning a themed activity, or just looking to inspire curiosity, these fun facts are grouped into four categories: freshwater fish, saltwater fish, deep-sea fish, and ancient fish. Get ready to learn about walking fish, glowing jaws, and creatures that haven’t changed in hundreds of millions of years.

Freshwater Fish Fun Facts

1. Diverse Species: Virginia alone hosts 226 species of freshwater fish. 

2. Scaleless Catfish: Members of the catfish family (Ictaluridae) lack scales, distinguishing them from many other fish. 

3. Swim Bladder Absence: Some darters (genus Etheostoma) lack swim bladders, helping them stay near stream bottoms. 

4. Nocturnal Habits: The Banded Sculpin (Cottus carolinae) is nocturnal, resting during the day and hunting at night. 

5. Colorful Perch: Virginia boasts 48 species of perch, often referred to as “aquatic butterflies” due to their vibrant colors. 

6. Arapaima Giants: The arapaima, native to the Amazon, can grow over 2 meters long and weigh around 90 kg. 

7. Mouthbrooding Males: Male arapaimas protect their young by carrying them in their mouths until they’re older. 

8. Ancient Lineage: Arapaimas have fossils dating back 23 million years, making them some of the oldest known freshwater fish. 

9. Slow Maturation: Arapaimas reach sexual maturity around the age of 55 and can live up to 100 years. 

10. Unique Breathing: Arapaimas can breathe air, allowing them to survive in oxygen-poor waters.

Saltwater Fish Fun Facts

1. Clownfish Symbiosis: Clownfish have a mutualistic relationship with sea anemones, gaining protection from predators.

2. Seahorse Fathers: Male seahorses carry and birth their young, a rarity in the animal kingdom.

3. Pufferfish Defense: Pufferfish can inflate their bodies to deter predators, sometimes reaching up to 35 inches in diameter. 

4. Mandarinfish Colors: Mandarinfish display vibrant blue and orange patterns, making them popular in aquariums.

5. Flying Fish: Some fish can glide above the water’s surface to escape predators, covering distances up to 400 meters. 

6. Sailfish Speed: The Indo-Pacific sailfish can reach speeds over 110 km/h, making it one of the fastest fish. 

7. Mudskipper Mobility: Mudskippers can “walk” on land using their pectoral fins, allowing them to traverse between water bodies. 

8. Handfish Locomotion: Handfish use their pectoral fins to “walk” along the seafloor, resembling hands. 

9. Wahoo Acceleration: The wahoo is among the fastest fish for its size, reaching speeds up to 78 km/h. 

10. Shark Diversity: There are over 500 species of sharks, ranging from the tiny dwarf lanternshark to the massive whale shark.

Deep-Sea Fish Fun Facts

1. Bioluminescent Lanternfish: Lanternfish produce light through bioluminescence and account for a significant portion of deep-sea biomass. 

2. Stoplight Loosejaw: This fish emits red bioluminescence, invisible to most prey, aiding in stealth hunting. 

3. Brownsnout Spookfish: It’s the only vertebrate known to use mirrors in its eyes to focus images. 

4. Tripod Fish: This fish uses elongated fins to “stand” on the seafloor, waiting to ambush prey.

5. Deep Scattering Layer: Mass migrations of mesopelagic fish create a sonar-reflective layer, once mistaken for the ocean floor. 

6. Vertical Migration: Many deep-sea fish migrate vertically daily, feeding near the surface at night and returning to depths by day. 

7. Red Coloration: Red hues render deep-sea fish nearly invisible in the ocean’s depths, as red light doesn’t penetrate far. 

8. Expandable Stomachs: Some deep-sea fish can consume prey larger than themselves, thanks to highly stretchable stomachs.

9. Low Metabolism: Deep-sea fish often have slow metabolisms, allowing them to survive in nutrient-scarce environments.

Ancient Fish Fun Facts

1. Coelacanth Rediscovery: Thought extinct for 70 million years, the coelacanth was rediscovered in 1938 off South Africa. 

2. Living Fossils: Coelacanths have remained relatively unchanged for millions of years, earning them the title “living fossils.”

3. Unique Fins: They possess lobe-finned limbs, providing insight into the evolution of terrestrial vertebrates.

4. Fat-Filled Notochord: Instead of a typical vertebral column, coelacanths have a notochord filled with oil, aiding buoyancy. 

5. Intracranial Joint: A hinge in their skull allows coelacanths to open their mouths wide, aiding in feeding. 

6. Electrosensory System: They have a rostral organ that detects electric fields, helping them navigate and hunt in the dark. 

7. Deep Habitat: They inhabit depths of 150 to 700 meters, often sheltering in underwater caves. 

8. Low Brain-to-Body Ratio: Despite their size, coelacanths have a small brain occupying only 1.5% of their cranial cavity. 

9. Conservation Status: Coelacanths are considered vulnerable due to their limited distribution and slow reproductive rate.

Fish may seem simple at first glance, but their adaptations, behaviors, and histories reveal just how complex and incredible life underwater really is. By exploring these four categories—from the common to the bizarre—you’re not just learning facts, you’re connecting students to the natural world in a meaningful way. Use this guide as a starting point for discussions, classroom games, or even art projects. At HelloSubs, we believe learning should always spark wonder—and fish are a perfect place to start.