# What Is the Biggest Fish in the Ocean? > The whale shark is the biggest living fish in the ocean. Despite its name and enormous size, it is a shark rather than a whale. This spotted giant feeds mainly by filtering plankton and small animals from seawater, a strategy very different... Canonical URL: https://www.argo.net/what-is-the-biggest-fish-in-the-ocean/ Byline: ARGO.net Editorial Team Published: 2026-08-30T14:03:22+00:00 Categories: Explainer, Nature ![Whale shark swimming under crystal clear water of ocean near surface under sunlights](https://www.argo.net/wp-content/uploads/2026/08/whale_shark_swimming_near_diver.jpg) The **whale shark** is the biggest living fish in the ocean. Despite its name and enormous size, it is a shark rather than a whale. This spotted giant feeds mainly by filtering plankton and small animals from seawater, a strategy very different from the large-prey hunting often associated with sharks. Its size record and feeding behavior answer separate questions about how the animal lives. Exceptional individuals have been reported at lengths above 50 feet, although measuring a moving animal at sea is difficult and typical adults are smaller. NOAA's [answer to the biggest-fish question](https://oceanservice.noaa.gov/facts/bigfish.html) identifies the whale shark first and the basking shark as the next-largest living fish. ## Whale sharks are sharks, not whales The whale shark's scientific name is **Rhincodon typus**. Like other sharks, it has a skeleton made primarily of cartilage, several exposed gill slits and no bony swim bladder. Its broad, flat head and terminal mouth distinguish it from many familiar predatory sharks. The word whale refers to scale rather than ancestry. Whales are air-breathing mammals that nurse their young. Whale sharks breathe by passing water over gills and belong to the **cartilaginous fishes**. Each animal carries a pattern of pale spots and stripes. Researchers use photographs of the area behind the gills to identify individuals, much as a fingerprint distinguishes people. The pattern also makes the species immediately recognizable. ## How large can a whale shark grow? NOAA Fisheries states that whale sharks can exceed 50 feet and weigh several tons. The [basking shark reaches about 35 to 40 feet](https://www.fisheries.noaa.gov/national/outreach-and-education/fun-facts-about-fascinating-fish), placing it second among living fishes. Maximum size is less certain than a simple record suggests. Old accounts may rely on estimates, damaged specimens or inconsistent measurement. Modern laser photogrammetry and comparisons with known objects improve accuracy without capturing the animal. Most whale sharks encountered by researchers do not approach the claimed maximum. Aggregations can contain many juveniles or one sex disproportionately, so observations from a famous site do not represent the entire population. Size also depends on age, but growth is difficult to follow. Whale sharks travel long distances and mature slowly. Researchers combine repeated photographs, tags and vertebral growth bands to reconstruct their life history. ## A huge mouth filters very small prey Whale sharks feed on plankton, fish eggs and small schooling animals. Water enters the broad mouth and passes across filter pads associated with the gills. Food remains behind and is swallowed. They can feed while swimming forward with the mouth open or use suction around dense prey patches. Vertical feeding has been observed when food concentrates near the surface. The behavior changes with currents and prey. Thousands of tiny teeth line the mouth, but they do not function like the cutting teeth of a great white shark. Filtration allows a very large body to exploit abundant small prey when ocean conditions concentrate it. ## Whale sharks travel through warm oceans The species occurs in tropical and warm-temperate seas around the world. Individuals visit coastal feeding sites, cross open ocean and dive into deep water. Satellite tags reveal long movements but also gaps when tags detach or fail to transmit. Seasonal gatherings form where plankton or eggs become abundant, including reef spawning events and productive upwelling zones. These aggregations make research and tourism possible, yet they represent only part of the annual cycle. The Smithsonian Ocean profile notes that [whale sharks are highly migratory](https://ocean.si.edu/ocean-life/sharks-rays/whale-shark). Protecting them consequently requires cooperation across national boundaries and the high seas. ## Scientists identify and track individuals **Photo-identification catalogs** match spot patterns from new images with previous sightings. A match can reveal that one shark returned years later or traveled between regions. Citizen photographs become useful data when location and date are reliable. Satellite and acoustic tags answer different questions. Satellite tags record broad movements and depth, while acoustic tags are detected near installed receivers. Neither method follows every minute of an animal's life. Biopsy samples provide information about genetics, sex and diet. Ultrasound has helped researchers study reproduction in live females. Even with these tools, where whale sharks mate and give birth remains poorly known. ## The largest fish faces human threats Whale sharks can be struck by vessels because they feed near the surface. Fishing gear may entangle them and targeted or incidental capture has reduced populations. Marine pollution and changes in prey may add pressure. The IUCN Red List classifies the [whale shark as Endangered](https://www.iucnredlist.org/species/19488/2365291). That assessment reflects population decline and continuing threats, while uncertainty remains about abundance in many regions. Wildlife tourism can support conservation and local economies, but crowded boats and swimmers may disturb feeding or cause injury. Codes of conduct establish approach distance, speed and limits on contact. International trade controls and national protections address deliberate catch. Reducing ship strikes requires information about movement and vessel traffic. Conservation must cover both gathering sites and migration corridors. ## Why the blue whale does not count The blue whale is much larger than a whale shark, but it is a mammal rather than a fish. It breathes air with lungs, maintains a warm body and gives birth to calves that drink milk. The largest bony fish is another category. Ocean sunfishes are the heaviest living bony fishes, while whale sharks and basking sharks have cartilaginous skeletons. The answer changes only when the question changes from all fish to one anatomical group. Calling the whale shark the biggest fish is therefore precise. It combines exceptional size with the defining anatomy of a shark. Its gentle feeding style also shows that body size says little by itself about how an ocean animal lives. Responsible encounters keep that distinction visible without forcing contact. Observers gain more from watching natural movement than from touching, feeding or blocking a shark's path. ## Reproduction remains one of the largest mysteries Whale sharks give birth to live young after eggs hatch inside the mother. Evidence comes from a pregnant female examined in 1995 that carried hundreds of embryos at different developmental stages. Genetic analysis indicated that the embryos could share one father, suggesting females may store sperm. One specimen cannot establish how often that occurs across the species. Very small free-swimming pups are rarely observed and no confirmed nursery has resolved where most births occur. The scarcity limits estimates of pregnancy length and reproductive interval. Slow maturation means population recovery may take many years after losses. Protecting large females can be especially important, but their movements remain less documented than those of juveniles at coastal aggregations. Researchers continue to combine ultrasound, hormones, genetics and tracking in the search for **whale shark breeding areas**. The gaps are a reminder that even the **largest living fish** can pass through much of its life beyond direct human observation. ## Feeding aggregations reveal ocean productivity Whale sharks gather where currents concentrate prey densely enough to reward filter feeding. Fish spawning, coral spawning and plankton blooms can create brief seasonal feasts. Researchers sample plankton and record temperature alongside shark counts. These data test whether an aggregation follows a particular prey source rather than mere warm water. Arrival dates can shift between years because currents and biological events vary. A missing aggregation does not by itself show that every animal has left the region permanently. Protecting a feeding site requires managing vessel speed, tourism and fisheries during the period sharks are present. The surrounding water that produces prey is as important as the visible gathering point. These events provide rare access to a species that spends much of its time offshore. Carefully managed **whale shark tourism** can support research while keeping **natural feeding behavior** intact for visiting sharks at the site. **Related reading:** [animals that live on coral reefs](https://www.argo.net/what-animals-live-in-coral-reefs/) and [marine biogeography](https://www.argo.net/what-is-marine-biogeography/). **Explore this topic:** [Are Horseshoe Crabs Really Crabs?](https://www.argo.net/are-horseshoe-crabs-really-crabs/) and [Are All Fish Cold-Blooded?](https://www.argo.net/are-all-fish-cold-blooded/).