Key Differences Between Bony Fish and Cartilaginous Fish with Examples and Comparison Table
Hundreds of millions of years of evolution have resulted in the formation of two varieties of fish that appear to be identical on the surface. The makeup of their skeletons, however, is the most visible difference between the two species of fish. Bony fish, as the name implies, have a skeleton built completely of bones, whereas cartilaginous fish have a skeleton made entirely of cartilage. There are around 20,000 different types of fish on the globe. Pisces is the superclass of the Chordata class. The explanation for this is that fish makeup more than half of the chordates. Fish are classed as Osteichthyes or Chondrichthyes in this category (bony fish or cartilaginous fish).
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Although phylum chordata includes a lesser number of species as compared to non- chordates, yet chordates show advanced evolutionary characters. This phylum derives its name from a structure, named notochord, and surely classifies Homo sapiens under its domain. The term chordata originated from two words of the Greek language, the chorda and the ata. The meaning of ‘chorda’ is a thick string and the meaning of ‘ata’ is to have, so an overall meaning of chordata is animals having notochords. Notochord supports the body of these animals. So, chordates are the animals in which notochord is present in any stage of their life-span. Animals that do not have notochord are known as non- chordates. In chordates, species of maximum live animals is Pisces group and minimum live animals is Amphibia group.
Classification of Cartilaginous Fish
Phylum: Chordates
Class: Chondrichthyes
Features of Chondrichthyes
The features of Chondrichthyes are briefly discussed below.
This class includes Cartilaginous fishes and they are marine in nature. Their endoskeleton is made up of cartilage and notochord is persistent throughout life. The exoskeleton over the skin is made up of placoid scales and these scales are like denticles and originate from the dermis of the skin. Their teeth are modified placoid scales, which are backward in direction. In these fishes, 5 - 7 pairs of gills are present, which open directly outside the body by gill slits. The operculum is normally absent in these fishes. In them, the mouth is present at the ventral surface of the head.
Jaws and teeth are present. Suspensorium of jaws is Hyalostylic type. Their Jaws are very powerful and animals are predaceous in nature. Air bladders and lungs are absent in them, as they have to swim constantly to avoid sinking. A spiral valve or scroll valve is found in their intestine to increase surface area along with this cloacal aperture is also present. Their liver is mainly bilobed. There is a special structure at the dorsal surface of the head in these fishes, which is called “Ampullae of Lorenzini” that works as a thermoreceptor. The genital duct of these organisms opens into the cloacal aperture. The mode of fertilization is internal as male fishes have “claspers” as copulatory organs, which are developed by the inner edges of pelvic fins. Most of them are Viviparous in nature.
Classification of Bony Fishes
Phylum: Chordata
Class: Osteichthyes
Features of Osteichthyes
The features of Osteichthyes are briefly discussed below.
This mainly includes bony fish. Fishes of this class are found in freshwater as well as marine water. The endoskeleton of these fishes is made up of bones, so these are called bony fishes. Their exoskeleton is made up of scales, which may be cycloid or ctenoid or ganoid type. Placoid scales are absent. In these types of fishes, respiration occurs by 4- pairs of gills. These gills are covered by an operculum at each side of the body. Their mouth is normally terminal or subterminal, teeth are found in jaws. The Suspensorium of the jaw is autostylic.
Helping respiratory organs in them is mainly air bladders. Lung fishes respire through air bladders. In other fishes, these air bladders are hydrostatic which help in maintaining a balance of the body and provide buoyancy. The spiracle is absent in them along with the scroll valve of the intestine. Cloaca is absent, in place of cloacal aperture annus is present, also no ampulla of Lorenzini. Their liver is trilobed and their tail is normally a homocercal type but sometimes it may be diphycercal type. Fishes are oviparous but may be ovoviviparous or viviparous.
Difference Between Bony Fish and Cartilaginous Fish
To conclude we can say that we have developed an understanding of the differences between bony fishes and cartilaginous fishes. We have also learnt about some of the important features of both the subsets of fish.
FAQs on Difference Between Bony Fish and Cartilaginous Fish Explained Clearly
1. What is the main difference between bony fish and cartilaginous fish?
The main difference between bony fish and cartilaginous fish is that bony fish have a skeleton made of bone, while cartilaginous fish have a skeleton made of cartilage.
- Bony fish (Osteichthyes) have a hard, calcified endoskeleton.
- Cartilaginous fish (Chondrichthyes) have a flexible skeleton made of cartilage.
- Bony fish usually have a swim bladder for buoyancy, while cartilaginous fish lack it.
- Cartilaginous fish often have multiple exposed gill slits, whereas bony fish have gills covered by an operculum.
2. What are examples of bony fish and cartilaginous fish?
Examples of bony fish include salmon and goldfish, while examples of cartilaginous fish include sharks and rays.
- Bony fish: salmon, tuna, goldfish, seahorse, cod.
- Cartilaginous fish: sharks, rays, skates, sawfish.
- Bony fish form the majority of modern fish species.
- Cartilaginous fish are mostly marine and include many large predatory species.
3. Do bony fish and cartilaginous fish have different types of skeletons?
Yes, bony fish have a skeleton made of bone, while cartilaginous fish have a skeleton made of cartilage.
- Bone is hard and calcified, providing strong structural support.
- Cartilage is lighter and more flexible than bone.
- The cartilaginous skeleton helps sharks and rays move efficiently in water.
4. How do the gills of bony fish differ from those of cartilaginous fish?
Bony fish have gills covered by an operculum, while cartilaginous fish have multiple exposed gill slits.
- In bony fish, a single operculum covers the gill chamber on each side.
- In cartilaginous fish, 5–7 separate gill slits are visible externally.
- This difference is a key feature used in fish classification.
5. What is the function of the swim bladder in bony fish?
The swim bladder in bony fish helps maintain buoyancy without constant swimming.
- It is a gas-filled sac located in the body cavity.
- By adjusting gas volume, the fish can rise or sink in water.
- Cartilaginous fish do not have a swim bladder and rely on oily livers and continuous movement for buoyancy.
6. How do the scales of bony fish differ from cartilaginous fish?
Bony fish have thin, flexible scales, while cartilaginous fish have rough, tooth-like scales called placoid scales.
- Bony fish typically have cycloid or ctenoid scales.
- Cartilaginous fish have placoid scales that reduce friction in water.
- Placoid scales give shark skin a rough texture.
7. Are bony fish and cartilaginous fish classified differently?
Yes, bony fish and cartilaginous fish belong to different classes: Osteichthyes and Chondrichthyes respectively.
- Osteichthyes: fish with a bony endoskeleton.
- Chondrichthyes: fish with a cartilaginous endoskeleton.
- This classification is based mainly on skeletal structure and other anatomical features.
8. How does reproduction differ between bony fish and cartilaginous fish?
Most bony fish show external fertilization, while cartilaginous fish usually have internal fertilization.
- Bony fish commonly release eggs and sperm into water (external fertilization).
- Cartilaginous fish use claspers for internal fertilization.
- Some cartilaginous fish are oviparous, ovoviviparous, or viviparous.
9. Why are cartilaginous fish considered more primitive than bony fish?
Cartilaginous fish are considered more primitive because they evolved earlier and retain ancestral features like a cartilaginous skeleton.
- The fossil record shows Chondrichthyes appeared before most modern bony fish.
- They lack certain advanced features such as a swim bladder.
- However, they are highly specialized and well-adapted predators.
10. Do bony fish and cartilaginous fish live in the same habitats?
Bony fish and cartilaginous fish can both live in marine habitats, but bony fish are also common in freshwater environments.
- Bony fish are found in oceans, rivers, and lakes.
- Cartilaginous fish are mostly marine, with a few species entering freshwater.
- Habitat diversity is greater in bony fish.
