Depending on the depth, the two oceanic zones are pelagic and demersal. The column of water of the open ocean constitutes the pelagic zone. Pelagic fish are found closer to the surface of the ocean if you can imagine a column of water with the ocean floor at its bottom and the ocean’s surface at its top.
The habitat zones of oceans differ significantly depending on whether they are near shore or in shallow waters. The depth of the water is one of the primary differences between these ecological zones and the locations where fish reside.
In general, water pressure increases and temperature decreases as the depth of the water increases. But you also get less sunlight penetration the deeper you dive. The organisms that reside there differ according to these variations in water pressure, water temperature, and amount of sunlight.
The pelagic zone covers 1,330 million km3 (320 million miles3) of the oceans and the mean average depth in this region is 3.68 kilometres (2.29 miles).
Table of Contents
- Pelagic Fish
- Demersal Fish
- Difference between Pelagic Fish and Demersal Fish
- Frequently Asked Questions (FAQs)
Pelagic Fish
Fish that reside in the pelagic zone of oceans or lakes are referred to as pelagic fish. Pelagic fish often live in the middle or top layers of the water. The ocean or marine pelagic water is the world’s largest aquatic ecosystem, and marine pelagic fish can be divided into oceanic and coastal varieties. Pelagic fish inhabit shallow water areas above the continental shelf where sunlight can easily penetrate.
Pelagic fish inhabit the deep ocean waters outside of the continental shelf. Depending on whether they are marine or coastal, pelagic fish often come in sizes ranging from small to enormous. Small pelagic fish inhabiting coastal areas include herrings and sardines as examples. Pelagic fish in the ocean are larger fish, such as sharks and tuna. They can swim quickly and have sleek bodies.
The distribution of pelagic fish depends on the availability of dissolved oxygen, light, temperature, pressure, nutrients, and salt content, as per the locations. Due to their migration, pelagic fish exhibit shoaling behaviour. To facilitate hydrodynamic drafting and act as an anti-predator mechanism, these fish assemble to form schools.
Demersal Fish
Fish that reside in the demersal region, also known as deep water or close to the sea floor, are referred to as demersal fish. The majority of demersal fish are located on the sand, gravel, mud, and rock-covered bottom. In other words, these fish can be found on or around the continental rise or slope.
Demersal fish are relatively widespread and active in deep water. Rays, brotulas, rattails, lumpfishes, batfishes, eels, hagfishes, and green-eyes are a few examples of demersal fish. Demersal fish have long, thin, muscular bodies with well-developed internal organs.
Demersal fish are bottom dwellers; they exist and consume in the open water column at the ocean floor. Benthic fish and benthopelagic fish are two additional categories of demersal fish. While benthopelagic fish float in the water above the ocean floor, benthic fish rest on the ocean floor.
Difference between Pelagic Fish and Demersal Fish
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Pelagic Fish |
Demersal Fish |
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Pelagic fish are those that reside in the pelagic zone of lakes or oceans, which is not close to the bottom or the shore. |
Demersal fish, also known as groundfish, dwell and feed on or near the bottom of lakes and oceans (the demersal zone). |
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Coastal and oceanic are the two types |
Benthic and benthopelagic are the two types |
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Streamlined body |
Flat, long and narrow body |
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It possesses terminal mouth, pointing forward |
It possesses inferior mouth, pointing downwards |
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Herrings, sardines, shark, and tuna are examples |
Rays, brotulas, rattails, lumpfishes, batfishes, eels, hagfishes, and green-eyes are examples |
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