SKIN OF FISHES|| INTEGUMENTRY SYSTEM || ZOOLOGY C || MILLER AND HARLEY

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Skin of Fishes: Structure and Functions

Fish skin is a complex, multi-layered organ that plays crucial roles in protection, respiration, camouflage, and sensory perception. It consists of two primary layers:

1. Epidermis (Outer Layer)


2. Dermis (Inner Layer, Contains Scales in Most Species)




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1. Structure of Fish Skin

A. Epidermis (Outer Layer)

Composed of living cells (unlike reptiles and mammals, which have a dead outer layer).

Contains mucous cells (goblet cells) that secrete mucus, which:

Reduces friction in water.

Protects against bacteria, parasites, and fungi.

Helps with osmoregulation (especially in freshwater fish).


Lacks keratinization (unlike terrestrial vertebrates).


B. Dermis (Inner Layer)

Thicker than the epidermis, contains connective tissue, blood vessels, and nerves.

Houses chromatophores (pigment cells responsible for coloration and camouflage).

Contains scales (in most fish), which are bony or cartilaginous structures embedded within the dermis.


C. Hypodermis (Subcutaneous Tissue)

A thin layer of fatty tissue that provides insulation and energy storage.

More developed in some fish (e.g., deep-sea or cold-water species).



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2. Types of Fish Scales (Derived from the Dermis)

Most fish have scales embedded within the skin for additional protection. There are four main types:

1. Placoid Scales (Dermal Denticles) – Found in sharks and rays (cartilaginous fish).

Tooth-like structure with enamel covering.

Reduces water resistance (helps in faster swimming).



2. Ganoid Scales – Found in gars, sturgeons, and bichirs.

Hard, diamond-shaped, non-overlapping scales.

Made of ganoine, a tough, enamel-like substance.



3. Cycloid Scales – Found in salmon and carp.

Thin, rounded, overlapping scales with smooth edges.

Allow flexibility and growth.



4. Ctenoid Scales – Found in perches and sunfish.

Similar to cycloid but with tiny comb-like projections (ctenii) for added protection.




Some fish, like catfish and eels, lack scales and rely solely on a thick mucus layer for protection.