Pisces Examples and Their Role in Aquatic Ecosystems
Pisces are aquatic creatures with gills that allow them to breathe. They don't have a genuine spine. Fresh, marine and brackish water may all contain fish. Fins are the motility organs in fish. Fins, on the other hand, can be paired or unpaired. Ichthyology is the study of fishes. Meanwhile, they are thought to have originated from sea squirts, which are similar to primitive fish.
Pisces Description
Pisces are true jawed vertebrates with specialised respiratory, excretory, and circulatory systems. Since the species in this class are poikilotherms, they are unable to control their own body temperatures. In essence, this category includes all fish.
They have breathing and motility organs that are associated with permanently aquatic life. The gills are the respiration organs, while the paired and damaged fins are the movement organs. They're all poikilothermous. In the phylum Pisces, catfish, goldfish, whales, sharks, and jellyfish are a few examples. Various interesting Pisces facts are known throughout the world.
General Characteristics of Pisces
The following are the distinct Pisces traits:
Aquatic vertebrates, either freshwater or marine, herbivorous or carnivorous, cold-blooded, oviparous, or ovoviviparous.
The body is normally streamlined and spindle-shaped, with some elongated snake-like features and a few dorsoventrally compressed features, and is divided into three parts: head, trunk, and tail.
True dermal fin-rays assist locomotion by paired pectoral and pelvic fins, as well as median dorsal and caudal fins. Propulsion is accomplished through the use of a muscular tail.
An exoskeleton of dermal scales, denticles, or bony plates covers the body surface, which is a striking characteristic of Pisces.
The endoskeleton is made up of cartilaginous or bone tissue. Vertebrae, either bone or cartilage, frequently replace the notochord. The presence of a well-developed skull and a system of visceral arches, the first pair of which forms the upper and lower jaws with the latter articulated with the skull.
Muscles are divided into myotomes, which have separate dorsal and ventral sections.
An alimentary canal with a distinct stomach and pancreas leads to the cloaca or anus.
Gills are the organs of breathing.
The heart is two-chambered and venous, with one auricle and one ventricle.
The mesonephros of the kidneys is number ten.
There are five sections in the brain. There are ten pairs of cranial nerves.
There is no tympanic cavity or ear ossicles. There are three semicircular canals in the internal ear.
There is a well-developed lateral line system.
The sexes are separated. Gonads are usually found in pairs. Gonoducts can either enter into the cloaca or open independently.
Internal or external fertilisation is present.
Types of Scales
Placoid Scales Diagram
Fish scales serve as the creature's exoskeleton, which makes sense considering that the word "exoskeleton" refers to a skeleton that is visible from the outside. Fish scales come in a variety of shapes and sizes, including placoid, ganoid, cycloid, cosmid, and ctenoid. Scales are thin, cornified structures that are tiny and thin.
Since cosmid scales were a distinguishing feature of many extinct fish such as ostracoderms and placoderms, they are no longer present (or only very rarely found) on fish in the wild today.
Placoid scales are the characteristic feature of cartilaginous fishes.
Ganoid scales resemble little rhomboids. On the skin of a fish, these diamond-shaped plates fit side by side. Ganoid scales are a distinctive feature of chondrosteans, a group of fish having a cartilage-based skeleton that includes sturgeon.
In addition to being thin and translucent, cycloid scales have a somewhat round look. Bone makes up the thin upper layer of these scales, while connective tissue makes up the lower layer. Bowfin, cod, carp, and some lungfish have cycloid scales on their bodies.
Ctenidium is the name for anything that has a comb-like look or design. Ctenoid scales feature comb-like projections on the rear as a result. The bodies of flounder and sunfish are covered in ctenoid scales.
Classification of Fishes/Pisces
The classification of fishes pdf contains three main classes which are described as follows:
Placodermi
It contains fish that are no longer alive.
All of them are armoured fish. Bony plates or shields serve as their exoskeletons.
They have a bony endoskeleton.
These fishes have an autodiastylic jaw suspension.
The caudal fin of a heterocercal is visible.
The jaws will not be supported by the hyoid arch.
There are primitive jaws visible.
They lasted until the Permian epoch of the Paleozoic era.
Both Bothriolepis and Climatius are examples of this class.
Elasmobranchi or Chondrichthyes
These fish are only found in the sea.
Placoid scales make up the exoskeleton.
Cartilage is the name for their cartilaginous endoskeleton.
Amphistylic or hyostylic jaw suspension.
There are 5-7 pairs of gills present.
The external gill holes are distinct from the internal gill openings. Operculum does not cover them.
There is a heterocercal caudal fin present.
Males display claspers in preparation for copulation.
These fishes lack an air bladder.
Example: Scoliodon and Pristis.
Osteichthyes
These fish can be found in the sea, freshwater, and brackish water.
The exoskeleton will be made up of cycloid, ctenoid, or ganoid scales.
Bony endoskeleton.
Jaws suspension is self-adjusting.
There is tuberculosis present.
Claspers are not present.
In most cases, an air bladder is present.
Example- Salmon and Neoceratodus.
Conclusion
The Pisces phylum includes the first jawed vertebrates, and the study of fish is called Ichthyology. They are aquatic (may be freshwater or marine). The traits of Pisces include the presence of a streamlined body covered with different types of dermal scales like Placoid, Cosmoid, Ganoid, Cycloid, and Ctenoid. Fish are cold-blooded animals. This simple division of superclass Pisces into three classes- Placodermi, Chondrichthyes, and Osteichthyes.
FAQs on Pisces: Definition, Features & Classification
1. What are the key characteristics that define an animal as a fish (Superclass Pisces)?
To be classified under the Superclass Pisces, an animal must have a specific set of features. They are exclusively aquatic vertebrates that breathe primarily through gills. Other key characteristics include having fins for movement and stability, a streamlined body, and typically being covered in scales. They are also cold-blooded, meaning their body temperature changes with the surrounding water.
2. What is the main difference between cartilaginous fish and bony fish?
The main difference lies in their skeleton and other features. Here’s a simple breakdown:
- Skeleton: Cartilaginous fish (Chondrichthyes) have a skeleton made entirely of cartilage. Bony fish (Osteichthyes) have a skeleton made of bone.
- Gills: Cartilaginous fish have visible gill slits that are not covered, while bony fish have their gills protected by a hard cover called an operculum.
- Swim Bladder: Most bony fish have a swim bladder to control buoyancy, which cartilaginous fish lack.
- Mouth Position: In cartilaginous fish like sharks, the mouth is usually located on the underside (ventral), whereas in bony fish, it is typically at the front (terminal).
3. Can you give some common examples of both cartilaginous and bony fish?
Certainly! Common examples help in understanding the two main classes of fish.
- Cartilaginous Fish (Chondrichthyes): This group includes sharks, rays, and skates. For instance, the Great White Shark and the Stingray are well-known examples.
- Bony Fish (Osteichthyes): This is a much larger group. Common examples include everyday fish like Rohu, Tuna, Salmon, and unique ones like the Seahorse and Flying Fish.
4. How do fish breathe underwater?
Fish breathe using special organs called gills. As water flows over the gills, dissolved oxygen is absorbed into the fish's bloodstream, and carbon dioxide is released out into the water. This process, known as gaseous exchange, is highly efficient and allows them to survive underwater. A few special types, like lungfish, have also developed lungs to breathe air.
5. Why are fish said to have a single circulatory system?
Fish are said to have a single circulatory system because their blood passes through the heart only once for each complete circuit around the body. Their heart has only two main chambers (an atrium and a ventricle). Blood is pumped from the heart to the gills to get oxygenated, then circulates to the rest of the body before returning to the heart. This is different from the double circulation found in mammals and birds.
6. How do the different fins on a fish help it survive in water?
Fins are not just for swimming; they serve various specific functions essential for survival. The caudal fin (tail fin) provides the main power for propulsion. The dorsal and anal fins prevent the fish from rolling or yawing. The pectoral and pelvic fins are used for steering, stopping, and hovering. Together, they give a fish incredible control and agility in the water.
7. What is the purpose of the swim bladder in bony fish?
The swim bladder, also known as an air bladder, is a gas-filled sac that plays a crucial role in controlling a fish's buoyancy. By adjusting the amount of gas in the bladder, a bony fish can stay at a specific water depth without having to waste energy on constant swimming. It helps them float, sink, or remain stationary with minimal effort.
8. What is the lateral line system and how does it help fish?
The lateral line is a highly sensitive sensory system found in most fish. It appears as a faint line running along each side of the body. It consists of a series of sense organs called neuromasts that detect movement, vibrations, and pressure gradients in the surrounding water. This system helps fish to navigate, avoid obstacles, find prey, and sense predators, acting like a form of 'remote touch'.
9. Are all animals that live in water considered fish? For example, is a whale a fish?
No, not all animals living in water are fish. This is a common misconception. A whale, for instance, is a mammal, not a fish. The key differences are that whales breathe air with lungs (they must surface to breathe), are warm-blooded, and give birth to live young which they feed with milk. Fish, on the other hand, breathe with gills, are cold-blooded, and most lay eggs.
