Table of Contents
In this types of scales in fishes with diagram article we will discuss about types of scales in fishes with diagram: placoid scales, cosmoid scale, ganoid scale, ctenoid scale, cycloid scale, modification of different types of scales in fishes with diagram, and importance of different types of scales in fishes.
Scales in Fishes
Many vertebrates have two types of scales on their exoskeleton: dermal and epidermal. The Malpighian layer of epidermis is cornified to make epidermal scales. They can be found in terrestrial vertebrates such as reptiles, birds, and mammals. Fishes have been given dermal scales that are mesenchymal in origin.
They can be thin, thick, calcareous, bony, or a combination of both. Most commonly, the arrangement of scales on a fish body is imbricated. To reduce friction, they overlap like roof tiles. However, sometimes the arrangement of fishes may be reversed. Anguilla is a mosaic-like pattern for freshwater eel. Lota is a different species. They can be separated in small increments or met at their edges.
Different Types of Scales in Fishes
Different types of scales in fishes are characterised based on their structure and shape. Different types of scales in fishes is often characteristics of the species.
1. Placoid Scales
Placoid scaling is a common feature of sharks and Elasmobranches. These are tiny denticles that can be embedded in the skin. There are two parts to a scale. The upper part is known as the ectodermal spine or cap. This is made from an enamel-like substance called vitreodentine, similar to a human tooth.
The vitreodentine is followed by a layer of dentine which encloses the pulp cavity. Platoid scale’s lower portion is made up of a disc-shaped basal plate that is embedded in the dermis and has a cap or spine protruding through the epidermis.
Different types of scales in fishes: Placoid Scales
Basal plates have a small opening through which blood vessels or nerves can enter the pulp cavity. Platoid scales can be modified in jaw teeth of sharks, in spines in dorsal Fins; in Squalus (spiny fish); in sting in stingrays, and in saw teeth from the Pristis.
2. Cosmoid Scales
Cosmoid scales can be found in both living (Latimaria), and extinct lobefins. The cosmoid and cycloid-shaped cosmoid scales in dipnoi are highly modified. The cosmoid structure is plate-like and has three layers. The outermost layer, known as vitreodentine, is thin, hard, and enamel-like. The isopedine innermost layer is made of vascularized, perforated bony substance.
Different types of scales in fishes: Cosmoid Scales
The middle layer is composed of cosmine, a hard non-cellular material. It is also characterized by many chambers and branching tubules. This type of scales can be grown from the bottom by adding new isopedine material.
Ganoid scales are thick, rhomboid. The outer layer is made up of ganoine, a hard inorganic substance. This substance is distinct from the vitreodentine found on placoid scaling. A cosmine-like layer with many branching tubes is next to the ganoid layer. The innermost layer is occupied by a bony layer of Isopedine. These scales grow both at the surface and at the edges.
Different types of scales in fishes: Ganoid Scales
This growth is caused by the addition to new layers of isopedine. Ganoid scales are most commonly found in the Polypterus or Lepidosteius. These fishes have ganoid scales that are rhombic plates-like. They fit edge to edge and cover the entire body. The ganoid scales of Acipencer are made into large bony scutes and arranged in five rows.
4. Ctenoid Scales
The posterior portion of the teeth is distinctive. Spiny-rayed Teleost’s also have Ctenoid Scales. They are placed in a way that the posterior edge of one scale overlaps that of the one behind. These scales have chromatophores at the posterior end.
Different types of scales in fishes: Ctenoid Scales
5. Cycloid Scales
The cycloid scale is without teeth or spines and appears cyclic. They can be found in modern lobe-finned fishes and soft-rayed Teleost’s. However, some spiny-rayed fishes like Lepidosteius have cycloid scaling. Micropterus has both cycloid as well as ctenoid scaling.
Different types of scales in fishes: Cycloid Scales
Some fishes, such as catfishes and Torpedo (electrical-ray), are completely scaleless or naked. They are tiny and deep embedded in the dermis of eels. They can become more localized in some fishes (chimaeras). Modified scales can be referred to as jaw teeth in sharks. Modifications to the scales are the teeth that form the saw of Pristis or the stingray.
The Acanthurus sturgeon fish’s tail scales have been modified to form sharp cutting blades. Ostracion is a coffer fish. The scales are made up of polygonal bony plates that articulate with each other to create a protective box. The scales of the globe-fish, Tetrodon, and the porcupine fish Diodon are elongated to create spines for protection.
Modified scales can also be seen in the jointed fin-rays and leptotrichia, which are bony fishes. The scales of the Cetorhinus basking shark have been modified to create gill-rakers. To allow for water to exit the canal, the scales along the fish’s lateral line become perforated. Scales of the Hippocampus and Syngnathus pipe-fish are fused to form protective bony rings around their bodies.
Importance of Scales
The body’s exoskeleton is protected by the scales. Scales are useful for broad classification. Platoid scales of Chondrichthyes are common among fishes. Ganoid scales can be found in primitive bony fishes. Cycloid and Ctenoid teleost’s have the cycloid or ctenoid. The scales can be useful for separating families and orders.
Siluroid fishes, on the other hand, are not scaleless and can be distinguished easily from cyprinoids. Scales are an important resource for information about fossil fishes as well as the classification of kitchen middens from extinct men. The study of the diets of piscivorous animals can be done using scales. Many species can be identified using the scales that run along the lateral lines and around the body.
The ctenoid and cycloid scales can be of great assistance in calculating the growth rate and age of fishes. Many species experience seasonal growth, which can be seen on the scale’s lines of growth. Some species, such as Salmo, can have spawning marks visible on their scales. This allows one to determine how many times a fish spawned.
Scales increase in size throughout the life of a fish, and they grow with it. Concentric lines form during growth, which allows age determination in many species, including salmon, trout and bass. Each species has a unique scale pattern. The arrangement, number, form, and structure of the scales plays an important role in the identification and classification fish species.
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