Mucus Has Antibacterial Properties

a light yellow seahorse swims in an aquarium with a blurry blue background

Biological Strategy

Ray-finned fishes

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Protect From Microbes

In living systems, microbes play important roles, such as breaking down organic matter and maintaining personal and system health. But they also pose threats. Bacteria can be pathogens that cause diseases. Some bacteria create colonies called biofilms that can coat surfaces, reducing their effectiveness–for example, inhibiting a leaf’s ability to photosynthesize. Living systems must have strategies for protecting from microbes that cause disease or become so numerous that they create an imbalance in the system. At the same time, living systems must continue living in harmony with other microbes. Some living systems kill microbes. Others repel without killing to reduce the chances that microbes will adapt to the lethal strategy and become resistant to it. For example, some pea seedlings exude a chemical that inhibits biofilm buildup.

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Fish

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

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Glands in the skin of bony fishes help protect the fish from bacterial infection via secreted mucus.

“The typical bony fishes — trout, herring, cod, and hundreds of other species — have scales made of very thin, flake-like pieces of bone, often fine enough to be transparent. They are usually more or less rounded in outline: cycloid scales have smooth edges, while ctenoid scales have a spiked or serrated trailing edge (diagram b). The scales grow in the dermis, the inner layer of the skin, and are covered by a fine epidermis or outer skin layer: each scale fits into its own little pocket of epidermis (diagram c). The skin contains glands emitting mucus which keeps the scales slippery and flexible (as an angler knows to his cost) and also acts as an anti-septic, protecting the fish from bacterial infection. The scales grow by adding rings around the edge; they grow fast in summer but little in winter, and thus leave seasonal growth lines by which the age of the fish can be estimated.” (Foy and Oxford Scientific Films 1982:86)

Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.

Last Updated August 18, 2016

References

Book

The grand design: Form and colour in animals

26/02/1983 | Sally Foy

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