What are scaleless fish?

Scaleless fish, in scientific terms known as cyclostomes, represent a small and unique group of primitive jawless vertebrates. In contrast to the majority of fish species that possess scales, scaleless fish are characterized by their smooth and naked skin, which lacks conventional fish scales typical of other species.

Scaleless fish can be categorized into two distinct lineages: hagfishes and lampreys. Both hagfishes and lampreys display notable structural differences and feeding behaviors.

Here's a brief overview of scaleless fish, with a focus on hagfishes and lampreys:

Hagfishes:

- They lack vertebrae and jaws, making them the most primitive living vertebrates.

- They inhabit deep marine environments.

- Hagfishes have an eel-like body form and are widely recognized for their unique defense mechanism of producing large amounts of slimy mucus when threatened.

- They mainly feed on dead or dying fish and other invertebrate species.

Lampreys:

- Lampreys exhibit a lifecycle that involves larval and adult stages.

- During their larval stage, they possess scales, but these scales are lost during metamorphosis as they mature into adults.

- Their feeding behavior varies according to species. Some, like the parasitic lampreys, have a sucker-like mouth used to latch onto other fish and suck their blood, while others feed by burrowing into the substrate to filter micro-organisms and organic matter.

- Some lamprey species migrate over long distances during certain stages of their life cycle.

While scaleless fish are indeed a minority compared to scaled fish, they occupy crucial ecological roles in their respective habitats, participating in the decomposition of organic matter on the ocean floor and serving as important prey for various marine predators.