Difference Between Bony and Cartilaginous Fish

Nature is characterized by its biodiversity in plants and animals, which allows the life of a great variety of very different species, although they share many similar qualities with each other. As is the case with fish, which despite sharing the same habitat, have great differences in their structure that make them very particular.

What are Bony Fish?

Bony fish or also known as osteichthyes, are those that have an internal bone skeleton in their structure, made up of pieces of bone and little presence of cartilage, which is their main characteristic that differentiates them from other species of fish. Another of the qualities of bony fish is that they are gnathostome vertebrates, which means that they have articulated jaws.

This type of fish is quite common to find among known species, such as trout, salmon, carp, herring, tuna, among others.

In addition to the skeleton, bony fish have other peculiarities that separate them from other groups of fish: their respiratory system is located inside the gill chamber, with a small opening on each side of the fish and away from other organs.

Similarly, many of the bony fish species have a swim bladder, which functions as a lung and allows them to move vertically, float at certain depths; but at the same time it fulfills its functions similar to the bladder.

The skeleton of these animals is divided into four parts, calling the central part of the fish axial ; cephalic , corresponds to the head; zonal , the area close to the pelvic and thoracic fins and lastly appendicular , which refers to the fins themselves. Moreover, its body is covered with scale like bony plates in rows with one end attached to the body and the other free.

The mouth of bony fish is recognized by the name of terminal mouth , which, having an extension of the dermal bones, makes precise movements but when damaged or lost they do not regenerate. Due to their teeth and the constitution of their digestive system, bony fish are usually mostly carnivorous, but there are species with a complex intestine and a simple stomach that makes their diet herbivorous.

Bony fish have separate sexual organs, which indicates that there are females and males of the same species, so they reproduce sexually, in some cases by external or internal fertilization, varying according to the species. They can be found mostly oviparous, but there are also cases of ovoviparous and viviparous.

What are Cartilaginous Fish?

Cartilaginous fish or known as chondrichthyans, are a type of fish whose skeleton is made up of cartilage, and not bones. Although they are not as diverse or numerous as bony fish, they are quite striking thanks to their varied morphological adaptations of large size, their predatory habits and their muscular constitution that make them particular and curious.

Among its main characteristics are, in addition to the absence of bones, that they lack a swim bladder, so they must remain swimming or perch on the bottom wherever they are. Its movement is possible by its fins or by a kind of scale that covers its body called dermal denticles, which provides better hydrodynamics.

With regard to their breathing, it occurs through the gills exposed to the outside in slits, so many species need to remain in motion for the water to pass through them, although there are others that pump water internally to their respiratory organs. , so they can remain still for a long time.

Similarly, their teeth are replaced quickly, continuously and serially, so they always have new teeth to replace those that are broken, damaged or loosened.

Cartilaginous fish species have a highly developed sense of smell, so they can easily follow a trail or detect small amounts of substances of interest. In the same way, they pick up vibrations through the lateral line. However, they do not have the same development in the sense of sight.

Reproduction in cartilaginous fish is sexual and dioecious, with internal fertilization and depending on the species they can be oviparous, viviparous or ovoviparous, with few offspring in each reproductive cycle. Nor has any behavior been observed on the part of these animals, for the care of the young, only in some cases the eggs are protected.

There are two classes of cartilaginous fish, among which are the elasmobranchs, which include sharks and rays that have a carnivorous tendency. There are also the holocephalians, of which there are currently few species, among which the chimeras stand out.