Difference Between Bony Fish And Cartilaginous Fish

Bony fish and cartilaginous fish represent two classes within the vertebrate kingdom, each characterized by unique anatomical features and evolutionary adaptations. Both groups inhabit aquatic environments. In simple terms, a bony fish (Osteichthyes) is one whose skeleton is made of bone, while a cartilaginous fish (Chondrichthyes) has a skeleton made of soft, flexible cartilage. A third type of fish, including eels and hagfish, is the group known as Agnatha, or jawless fish. Let’s look at differences in details.

What is a Bony fish?

Bony fish also referred to as Osteichythyes is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue. Bony fish is the largest class of vertebrates in existence today. The group comprises of 45 orders, over 500 families and over 27000 species. A large majority of fish in existence today are members of taxonomic group, osteichthyes.  Virtually all other fish fall into the class of bony fish.

Examples of bony fish include:

• Salmon
• Sea Horse
• Cod
• Tuna
• Tilapia
• Herring
• Catfish
• Coelacanth
• Muskellunge
• Goldfish
• Piranha
• Sturgeon
• Wahoo

All bony fishes have sutures in their neurocranium and segmented fin rays derived from their epidermis. Both bony fish and cartilaginous fish breathe through gills, but bony fish also have a hard, bony plate covering their gills. This feature is called an “operculum.” Bony fish may also have distinct rays, or spines, in their fins.

Bony fish can be found in waters all around the world, freshwater and saltwater both, unlike cartilagenous fish who are found only in salt waters. Marine bony fish live in all the oceans, from shallow to deep waters, and in both cold and warm temperatures. Their lifespans range from a few months to over 100 years.

Bony fish behavior varies greatly, depending on the species. Smaller bony fish swim in schools for protection. Some like the tuna swim continually while others (stonefish and flatfish) spend most of their time lying on the seafloor. Some such as morays only hunt at night; some like butterfly fishes do so during the day; and others are most active at dawn and dusk. 

Characteristics You Need To Know About Bony Fish (Osteichthyes)

• The endoskeleton of bony fish is completely made up of bones.
• Most of the bony fish are found in both saltwater and freshwater habitats.
• In bony fish, the gills are covered by an external flap of skin referred to as the operculum.
• In bony fish, red blood cells are produced in the bone marrow, the central part of the bone. This process is referred to as hemopoiesis.
• Bony fish have a swim bladder that which helps to maintain neutral buoyancy. A swim bladder is typically two-sac organ that controls the volume of internal gases to help the fish maintain a certain position in water.
• The intestines of bony fish are longer and do not a spiral shape.
• Bony fish have two sets of jaws: oral jaw and the pharyngeal jaw.  The oral jaw allows the fish to catch food, to bite it, and to chew it.  Teeth only grow along one side of the jaw.
• In bony fish, reproduction is external. The fish produce a significant number of small eggs with very little yolk. The eggs are released into the open waters, among rocks in the river and seabed. Male fish swims over the laid eggs, fertilizing them with sperm. The sperm may or may not fertilize all of the eggs.
• Their exoskeleton is made up of cycloids (thin bony plates), aligned based on whether the outer edges are spiny or smooth.
• The buccal cavity (mouth) of bony fish is at the anterior tip of the body.
• Osteichthyes can be carnivores, omnivores, herbivores, filter-feeders or detritivores.
• They excrete ammonia.
• The tail is homocercal, the vertebral column ends at the middle of the base of the caudal fin.
• Stomach is not differentiated into cardiac and pyloric regions. The intestinal caecum is present.
• Kidney renal, fused with a broad anterior and a narrow posterior portion.
• Examples of osteichthyes include Labeo, catla, Hilsa, Wallago, Hippocampus, globe fish, sea horses, eels, rohu, salmon fish, flying fish etc.

What is Cartilaginous fish?

Cartilaginous fish also referred to as chondrichthyes fish are fish that have a skeleton made of cartilage, rather than bone. Cartilaginous fish are jawed vertebrates with paired fins, paired nares, scales, a heart with its chambers in series and skeletons made of cartilage rather than bone.

In addition to the difference in their skeletons, cartilaginous fish have gills that open to the ocean through slits, rather than the bony covering that is present in bony fish. Different shark species may have different numbers of gill slits.

Cartilaginous fish may also breathe through spiracles, rather than gills. Spiracles are found on top of the heads of all rays and skates, and some sharks. These openings allow the fish to rest on the ocean bottom and draw oxygenated water in through the top of their head, allowing them to breathe without breathing in sand.

Cartilaginous fish live all around the world, in all kinds of water – from rays that inhabit shallow, sandy bottoms to sharks that live out in the deep, open ocean.

Examples of cartilaginous fish include:

• Skates
• Rays
• Chondrichthyan
• Sawfish
• Electric ray
• Guitarfish
• Cladoselache
• Chimaeras
• White Shark
• Smooth hound
• Stingray
• Tiger shark
• Manta Ray
• Hammerhead shark
• Globlin Shark

Also Read: Difference Between Bone And Cartilage

Characteristics You Need To Know About Cartilaginous Fish (Chondrichthyes)

• In cartilaginous fish, the endoskeleton is completely made up of cartilages.
• Most of the cartilaginous fish survive in marine or saltwater habitats.
• In cartilaginous fish, the gills are exposed and not protected by any external skin.
• Cartilaginous fish lack bone marrow for hemopoiesis; instead they produce red blood cells in the spleen and thymus organ.  
• Cartilaginous fish do not have swim bladder; they are able to achieve neutral buoyancy due to the lighter weight of their cartilaginous skeleton and their more hydrodynamic exteriors. Some cartilaginous like the sharks swim to the surface to take in air that helps them to maintain any position in water.  
• The intestines of a cartilaginous fish are short and spirally shaped in order to create a larger surface area that maximizes absorption of nutrients.
• Cartilaginous fish does not have pharyngeal jaw. The oral jaw of these fish is comprised of cartilage and separated into an upper and lower section. Each section is able to hold a number of teeth, which grow in multiple sets. 
• In cartilaginous fish, reproduction occurs internally. The sperm is deposited inside of the female in order to fertilize a small number of large sized eggs with a significant amount of yolk.
• The exoskeleton of cartilaginous fish is made up of placoid (very small denticles coated with lots of sharp enamel).
• The buccal cavity (mouth) of cartilaginous fish is ventrally positioned.
• Chondrichthyes are generally carnivores.
• They excrete urea.
• The tail is heterocercal, the vertebral column extending into the dorsal part of the caudal fin.
• The stomach is differentiated into cardiac and pyloric regions. The intestinal caecum is absent.
• The kidneys are elongated and narrow with anterior non-renal and posterior renal portion.
• Examples of chondrichthyes include Scolidon, Electric ray torpedo, string ray, sharks, dog fish, skates etc.

Also Read: Difference Between Vertebrates And Invertebrates

Bony Fish vs Cartilaginous Fish In Tabular Form