Difference Between Cartilaginous Fish and Bony Fish

Cartilaginous Fish vs Bony Fish

These two types of fish make up almost all the fish species living on the Earth. Altogether, there are 28,000 species of bony and cartilaginous fish. They exhibit a range of differences between them that makes it interesting to perform a comparison.

Cartilaginous Fish

In cartilaginous fish, it is a cartilage skeleton rather than bones as the name indicates. Sharks, skates, rays are prime example for living cartilaginous fish. There is no connection between their upper jaw and skull, so that they can move it independently. The skull comprises of 10 cartilaginous parts and they have eyelids to protect their eyes. Cartilaginous fish do not have ribs and no bone marrow. Therefore, the production of red blood cells takes place in the spleen. Dermal denticles cover the whole skin and those are similar to the structure of our teeth. The mouth is sub-terminal, i.e. located ventrally in cartilaginous fish. They do not have an operculum to cover the gills, and there are 5 – 7 gill slits remain open at all the times. Their caudal fin is not symmetric, and the two lobes of the fin are unequal in size. Another interesting feature is that their pectoral fin is parallel to the longitudinal axis of the body, which helps them to balance their body rather than providing power to swim through the water column. Their lightweight skeleton along with the oil-filled liver provide buoyancy against the heavy body. Their heavy weight could crush the internal organs outside water (e.g. shark). They excrete urea as the nitrogenous waste product. They are living fossils, because cartilaginous fish started to evolve before 420 million years, and presently there are over 970 species living in the sea.

Bony Fish

As their name indicates, they have a bony skeleton, which is calcified and ossified. Their upper jaw connects with the skull, and the skull has 63 tiny bony parts. Bony fish keep their eyes always open, as they do not have eyelids. They have scales covering all over the body, and the caudal fin is symmetric. In addition, their pectoral fin is perpendicular to the longitudinal axis of the body. Bony fish have gas-filled swim bladder, which is useful for buoyancy. They have a flap to cover the gills called operculum. Bony fish excrete ammonia as their nitrogenous waste product. Bony fish inhabit both freshwater and saltwater, and there are more than 27,000 extant species of them. Moreover, bony fish account for more than half of all the vertebrate species on the Earth.

Difference between Cartilaginous Fish and Bony Fish

Cartilaginous fishBony fish
More than 970 species, and inhabit only marine environmentMore than 27,000 species, and inhabit both freshwater and saltwater
Cartilaginous endoskeletonBony endoskeleton
Open gill slitsOperculum to cover gills
Upper jaw moves independently, as it does not connect with the skullUpper jaw connects with the skull
Dermal denticles cover the bodyScales cover the body
Asymmetric caudal finSymmetric caudal fin
Pectoral fin is parallel to the longitudinal axis of the bodyPectoral fin is perpendicular to the longitudinal axis of the body
Oil-filled liver for buoyancyGas-filled bladder for buoyancy
Always a sub-terminal mouthMouth could be either terminal or sub-terminal or supra-terminal according to the living habitat in the water column
Nitrogenous waste is ureaNitrogenous waste is ammonia