Some People Don’t Think Fish Are Animals. Here’s What Science Says

The classification of living things isn’t always simple, and it’s easy to feel confused about whether fish are animals or something else entirely. Let’s dive into the science to clear things up.

Biologists group all living things into categories called “kingdoms.”

The animal kingdom sits alongside others, like plants, fungi, and bacteria. Even within science, there’s debate about how many kingdoms exist, so it’s no wonder some confusion arises.

So, are fish animals? The answer is yes! Here’s why…

Fish Are Animals – According to Science

Biologists classify fish as animals. In fact, fish belong to one of the six main groups of animals: mammals, birds, reptiles, amphibians, fish, and invertebrates.

While the flesh of fish might not always be called “meat,” fish are undeniably animals with brains and the ability to feel pain.

Scientists agree that the animal kingdom includes a vast range of creatures, from microscopic plankton to whales. Fish, with their unique adaptations like fins and gills, are textbook examples of what it means to be an animal.

Surprising insight: Many invertebrates, like jellyfish, sponges and coral, are also classified as animals, despite lacking backbones or nervous systems. Jellyfish, for example, have a simple nerve net that helps them detect stimuli.

What Makes an Animal an Animal?

To qualify as an animal, organisms must meet specific criteria:

1. Made of multiple cells
2. Consume food for energy
3. Reproduce sexually
4. Composed of cells without walls
5. Capable of motion at some stage of life
6. Respond to external stimuli

Fish tick all these boxes, making them animals just like pigs, parrots, and people.

What Type of Animals Are Fish?

Fish are vertebrates, meaning they have backbones, just like mammals, birds, and reptiles. They’re a distinct category of animals, and their features make them truly unique.

Key Features of Fish:

• Live in water
• Have gills for breathing
• Possess scales and fins

Fish range in size from the tiny dwarf minnow (1 cm) to the massive whale shark (up to 10 metres). They can also be grouped into three main types:

1. Bony Fish – Tuna, salmon, and cod
2. Cartilaginous Fish – Sharks and rays
3. Jawless Fish – Hagfish and lampreys

Fish are incredibly diverse, with over 32,000 species—more than all mammals, birds, reptiles, and amphibians combined.

Not everything with “fish” in its name is a true fish, though. For instance:

• True Fish: Sharks, rays, eels, seahorses
• Not Fish: Whales, dolphins, starfish, jellyfish

The defining traits of fish are their gills, fins, and fully aquatic lifestyle. While other animals may have one or two of these features, only fish combine all three.

The Language Problem

Part of the confusion comes from how we talk about fish. Terms like “seafood” and “catch of the day” reduce fish to commodities, stripping them of their identity as living beings. These phrases condition us to see fish as food first, and animals second.

Fish are also less visible in conservation campaigns compared to pandas, elephants or tigers. This absence from public consciousness reinforces the misconception that they’re less important, or less “animal.” Shifting the narrative begins with recognising fish as living beings with intrinsic value.

By reframing the way we speak about fish, and emphasising their intelligence and ecological importance, we can help shift public perception toward greater respect for these creatures.

Why Do Some People Think Fish Aren’t Animals?

Some people associate animals with mammals, like dogs or cows, and may not realise that the animal kingdom includes fish and marine life.

Another reason why people may think that fish are not animals is because of the Catholic doctrine which states that Catholics must abstain from eating meat on Fridays, but that they can eat fish. 

This may cause some people to wrongly conclude that…

• Fish isn’t considered to be meat (TRUE)
• Meat is made from animals (TRUE)
• Therefore, fish are not animals (FALSE)

This type of faulty reasoning is known as a fallacy.

Is Fish Considered Meat?

The answer depends on the context:

• Religious Context: Meat is defined as warm-blooded animal flesh, so fish isn’t considered meat.
• Scientific Context: Meat includes all animal flesh, including fish.

Even dictionaries differ on this. For example:

• Cambridge Dictionary defines meat as “the flesh of an animal used for food,” including fish.
• Merriam-Webster specifies meat as “the flesh of mammals, as opposed to fowl or fish.”

Fish Have Brains and Feel Pain

Yes, fish have brains — just like most animals. Some exceptions, such as jellyfish and sea sponges, lack brains, but these aren’t fish. (They are animals, though).

Scientific evidence suggests that fish do feel pain. They have neurons called nociceptors that detect injury and stress. In fact, fish produce pain-relieving opioids, much like mammals

In 2013, the American Veterinary Medical Association published guidelines for the euthanasia of animals, which included the following statements: “Suggestions that finfish responses to pain merely represent simple reflexes have been refuted. … the preponderance of accumulated evidence supports the position that finfish should be accorded the same considerations as terrestrial vertebrates in regard to relief from pain.”

Fish can recognise faces, form social bonds and even display personalities. These emotional and cognitive abilities challenge our assumptions about what it means to be a sentient animal.

Goldfish, for instance, can remember things for months (so much for that three-second memory myth). Cleaner wrasses have even passed the mirror test, a classic experiment that measures self-awareness.

Should You Eat Fish?

The choice to eat fish is personal, but it’s worth considering a few facts:

Benefits:

• Fish are rich in omega-3 fatty acids, vitamins, and minerals.

Drawbacks:

• Fish feel pain during capture and death
• Commercial fishing harms dolphins, turtles, and other marine animals
• Overfishing damages ecosystems
• Fish can contain harmful toxins like mercury, especially in polluted waters

The NHS advises children, pregnant women, and breastfeeding mothers to limit fish consumption due to these pollutants.

Of course, it’s up to each individual to decide what they are comfortable with eating, after learning the facts. Here are some definitions of different dietary groups…

• Vegetarians: Do not eat fish, as it’s the flesh of an animal
• Vegans: Avoid all animal products, including fish
• Pescatarians: Avoid meat but eat fish and seafood
• Seagans: Follow a vegan diet but include fish and seafood.

Read more: The Different ‘Levels’ Of Vegan – Which Are You?

Can Vegans Keep Pet Fish?

The ethics of keeping pet fish is a hot topic. While rescuing unwanted goldfish and providing a proper habitat may align with vegan values, keeping wild-caught tropical fish in small tanks is generally frowned upon.

The Bottom Line

Fish are animals. They feel pain, have brains, and meet all the biological criteria for being animals. While some definitions of meat exclude fish, this doesn’t change their status as animals.

Whether or not you choose to eat fish, understanding their biology, sentience, and the environmental impact of fishing can help you make informed decisions.

Fish face serious threats: pollution (oil and plastic, for example), overfishing and climate change are wreaking havoc on their habitats. Recognising fish as animals is step one.

Step two? Advocating for their protection.

Every ripple of change we make today helps protect their legacy for generations to come.

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