Bony Fish vs. Sharks

What's the Difference?

Bony fish and sharks are both members of the class Chondrichthyes, but they have distinct differences. Bony fish, such as trout or salmon, have skeletons made of bone, while sharks have skeletons made of cartilage. Bony fish have a swim bladder that helps them control their buoyancy, while sharks rely on their large livers filled with oil to stay afloat. Additionally, bony fish have scales that protect their bodies, while sharks have rough, tooth-like scales called dermal denticles. In terms of reproduction, bony fish lay eggs, while most sharks give birth to live young. Despite these differences, both bony fish and sharks are fascinating creatures that have adapted to their aquatic environments in unique ways.


Bony Fish
Photo by Karl Callwood on Unsplash
AttributeBony FishSharks
SkeletonBony skeletonCartilaginous skeleton
GillsOperculum covers gillsGills exposed
Swim BladderPresentAbsent
ReproductionExternal and internal fertilizationInternal fertilization
Body ShapeVaries, can be streamlined or flatStreamlined
TeethVaries, can have different types of teethMultiple rows of sharp teeth
SizeVaries, can range from small to largeVaries, can range from small to large
Scale TypePlacoid scalesGanoid or placoid scales
Number of FinsVaries, typically have paired finsVaries, typically have paired fins
Photo by Jakob Owens on Unsplash

Further Detail


Bony fish and sharks are two distinct groups of fish that have evolved over millions of years to adapt to their respective environments. While both belong to the class of fish known as Chondrichthyes, they differ significantly in their physical attributes, behavior, and ecological roles. In this article, we will explore the key differences and similarities between bony fish and sharks, shedding light on their unique characteristics.

Anatomy and Physical Attributes

Bony fish, as the name suggests, possess a skeleton made primarily of bone. They have a wide variety of body shapes, ranging from slender and elongated to laterally compressed. Their scales are typically covered with a slimy mucus layer, which helps reduce friction in the water. Bony fish also have a swim bladder, an internal gas-filled organ that aids in buoyancy control.

On the other hand, sharks have a cartilaginous skeleton, which is lighter and more flexible than bone. Their bodies are streamlined and cylindrical, allowing them to move swiftly through the water. Instead of scales, sharks have dermal denticles, which are tooth-like structures that provide protection and reduce drag. Sharks lack a swim bladder, relying on their large oily liver to control buoyancy.

Respiration and Circulation

Bony fish respire using gills, which extract oxygen from the water. They have a specialized flap called an operculum that covers the gills, protecting them while allowing water to flow over them. Bony fish also have a two-chambered heart, with one atrium and one ventricle, which pumps oxygenated blood to the body and deoxygenated blood to the gills for oxygenation.

Sharks, on the other hand, also respire through gills, but they lack an operculum. Instead, they rely on their constant forward motion to force water over their gills, ensuring a constant supply of oxygen. Sharks have a more advanced circulatory system compared to bony fish, with a two-chambered heart that is more efficient at pumping oxygenated blood to the body. They also have several additional blood vessels, known as lateral aortas, which help distribute oxygen-rich blood to their muscles.

Feeding Habits and Teeth

Bony fish exhibit a wide range of feeding habits, depending on their species. Some are herbivorous, feeding on algae and plants, while others are carnivorous, preying on smaller fish, invertebrates, or even other bony fish. Bony fish have a variety of tooth shapes and sizes, adapted to their specific diet. For example, herbivorous bony fish have flat, molar-like teeth for grinding plant material, while carnivorous species have sharp, pointed teeth for capturing and tearing prey.

Sharks, on the other hand, are primarily carnivorous predators. They have rows of sharp, triangular teeth that are continuously replaced throughout their lifetime. Some sharks, like the great white shark, have serrated teeth for cutting through flesh, while others, like the whale shark, have small, filter-feeding teeth to capture plankton. Sharks are known for their powerful bite force and ability to consume large prey.

Reproduction and Life Cycle

Bony fish exhibit a wide range of reproductive strategies. Some species lay eggs externally, while others give birth to live young. Many bony fish engage in complex courtship rituals and build nests to protect their eggs. After hatching, the larvae go through various stages of development before reaching adulthood. The time it takes for bony fish to reach sexual maturity varies greatly depending on the species.

Sharks, on the other hand, have a more diverse range of reproductive strategies. Most sharks are ovoviviparous, meaning the eggs develop and hatch inside the female's body, with the young being born live. However, some species are oviparous, laying eggs externally, while others are viviparous, where the embryos receive nourishment from the mother through a placenta-like structure. Sharks generally have a slower growth rate and longer lifespan compared to bony fish.

Ecological Roles and Conservation

Bony fish play a crucial role in aquatic ecosystems as both predator and prey. They contribute to the overall biodiversity and help maintain the balance of marine food webs. Many bony fish species are commercially important for human consumption and support global fisheries. However, overfishing and habitat destruction pose significant threats to their populations, necessitating sustainable fishing practices and conservation efforts.

Sharks, as apex predators, play a vital role in regulating marine ecosystems. They help control the populations of prey species, preventing cascading effects throughout the food chain. Sharks are also highly vulnerable to overfishing, primarily driven by the demand for their fins in the shark fin trade. Many shark species are currently endangered or threatened, highlighting the need for conservation measures to protect these important marine predators.


In conclusion, bony fish and sharks are two distinct groups of fish with unique attributes and ecological roles. Bony fish have a bony skeleton, swim bladder, and a variety of feeding habits, while sharks have a cartilaginous skeleton, lack a swim bladder, and are primarily carnivorous. Understanding the differences between these two groups helps us appreciate the incredible diversity and complexity of the underwater world. It also emphasizes the importance of conservation efforts to ensure the survival of both bony fish and sharks for future generations.

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