Fish are among the most diverse and ancient groups of vertebrates, with over 30,000 species living in various aquatic habitats.

Many fish have evolved protective features such as spines, scales, and armor to cope with the challenges and threats of their environment.

Explore the evolution of bony and scaly armor in fish, focusing on the role of a special type of stem cells called trunk neural crest cells.

Looking at some examples of fish that have retained their ancestral armor, such as sturgeons and catfish, and how they use it for defense, camouflage, and communication.

What is dermal armor?

(Photo : Sebastian Pena Lambarri/ via Unsplash)

Dermal armor is a term that refers to any hard or tough covering on the skin of an animal that provides protection from predators, parasites, or environmental factors, as per Caltech.

It can be made of different materials, such as bone, dentine, keratin, or chitin. Dentine is a mineralized tissue that forms the main part of teeth and is also found in some fish scales and spines.

Dermal armor can have various shapes and patterns, such as plates, scales, spines, tubercles, or scutes. Plates are large flat pieces of armor that cover a large area of the body. It also have different functions, such as protection, camouflage, communication, or thermoregulation.

Protection is the most obvious function of dermal armor, as it can deter or injure potential predators or parasites.

Camouflage is another function of dermal armor, as it can help the animal blend in with its surroundings or mimic other animals.

Communication is another possible function of dermal armor, as it can signal information about the animal's identity, status, mood, or intentions to other members of its species or other animals.

Thermoregulation is another potential function of dermal armor, as it can help the animal regulate its body temperature by reflecting or absorbing heat.

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Fish evolves dermal armor

The evolution of dermal armor in fish is a complex and fascinating topic that involves multiple factors and processes. One of the key factors is the role of trunk neural crest cells, as per Phys.org.

Trunk neural crest cells are a type of stem cells that originate from the spinal cord region of vertebrate embryos.

They have the ability to migrate throughout the developing body and differentiate into various cell types and tissues.

Some of the structures that trunk neural crest cells contribute to include pigment cells, nerve cells, cartilage cells, bone cells, and dentine cells.

Trunk neural crest cells are responsible for the development of dermal armor in fish. They migrate to the skin layer and interact with other cell types to form bone- or dentine-based structures such as scales, spines, or scutes.

The shape and pattern of these structures depend on various factors such as genetic regulation, environmental cues, mechanical forces, and cellular interactions.

The evolution of trunk neural crest cells and their role in dermal armor formation is an example of evolutionary innovation and diversification.

Dermal armor was one of the first adaptations that gave vertebrates an advantage over their predators and competitors in the aquatic environment. Dermal armor also allowed vertebrates to explore new ecological niches and habitats.

Which fish have bony and scaly armor?

Many fish have evolved bony and scaly armor over millions of years of evolution. However, some fish have retained their ancestral forms of dermal armor more than others. These fish are often considered living fossils because they have changed little since their origin.

One example of such fish is sturgeons (Acipenseridae), a family of large freshwater or anadromous fish that inhabit temperate regions of Eurasia and North America.

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