What is the Difference Between Pelagic and Demersal Fish

The key difference between pelagic fish demersal fish is that pelagic fish inhabit the mid-water regions or upper layers of water while demersal inhabit the bottom layers of water or near the ocean floor.

Pelagic and demersal are the two zones in the oceans, depending on the depths. Pelagic zone is the mid-water region or the upper layers of the water. Thus, fish varieties living in the pelagic zone are known as pelagic fish. Demersal zone is the deeper layers of the water or water near the bottom of the ocean floor. Therefore, fish varieties living in the demersal zone are known as demersal fish.

CONTENTS

1. Overview and Key Difference
2. What is Pelagic Fish
3. What is Demersal Fish
4. Similarities – Pelagic and Demersal Fish
5. Pelagic vs Demersal Fish in Tabular Form
6. Summary – Pelagic vs Demersal Fish

What is Pelagic Fish?

Pelagic fish refers to fish that live in the pelagic zone of the ocean or lakes. Pelagic fish usually occupy the mid-water region or upper layers of the water. The marine pelagic water or ocean is the largest aquatic habitat on earth, and marine pelagic fish can be classified as coastal fish and oceanic fish. Coastal pelagic fish live in shallow regions of water where sunlight penetrates easily, typically above the continental shelf. Oceanic pelagic fish live in deep waters of the ocean beyond the continental shelf. Pelagic fish usually range in small to large sizes, depending on whether they are coastal or oceanic.

Coastal pelagic fish are small in size, and herrings and sardines are two examples of this kind of fish. Oceanic pelagic fish are larger in size and include tuna and sharks. They have a streamlined body and are fast swimmers. The distribution of these fish is dependent on the availability of light, dissolved oxygen, nutrients, pressure, temperature, and salinity, according to the regions. Pelagic fish are migratory thus, show shoaling behavior. That is where they form schools of fish, which allow them hydrodynamic drafting that also serves as an anti-predatory mechanism.

What is Demersal Fish?

Demersal fish are fish that live in deep water or near the bottom of the sea, which is also known as the demersal region. Most demersal fish are found on the seafloor, which consists of mud, gravel, sand, and rocks. In other words, these fish are found on or near the continental slope or the continental rise. In deep water, fish are relatively abundant and very active. Examples of demersal fish include rays, rattails, brotulas, eels, batfishes, lumpfishes, hagfishes, and greeneyes. The bodies of demersal fish are long, narrow, and muscular, with well-developed organs.

Demersal fish are bottom feeders; they live and eat at the bottom of the ocean in the open water column. Demersal fish are also classified into two groups as benthic fish and benthopelagic fish. Benthic fish rest on the ocean floor, whereas benthopelagic fish float in water just above the ocean floor. Benthic fish are much denser and have negative buoyancy; therefore, they have the ability to lie on the ocean floor. Benthopelagic fish have neutral buoyancy to float at a high depth without much effort. The majority of demersal fish are found to be benthopelagic fish.

What are the Similarities Difference Between Pelagic and Demersal Fish?

• Both pelagic and demersal fish live and feed in the ocean.
• They respire through gills.
• Both pelagic and demersal fish are cold-blooded and vertebrates.

What is the Difference Between Pelagic and Demersal Fish?

Pelagic fish occupy the mid-water region or upper layers of the waters, while demersal fish are found on the seafloor or in deep water near the ocean floor. So, this is the key difference between pelagic and demersal fish. Since demersal fish feed and live in the bottom layers of water, their buoyancy is higher than pelagic fish. Most pelagic fish exist and swim as a shoal of fish whereas, most demersal fish exist and swim individually.

The below infographic presents the differences between pelagic and demersal fish in tabular form for side by side comparison.

Summary – Pelagic vs Demersal Fish

Most fish live in the ocean, which is the largest water reserve on earth. Pelagic fish usually occupy the mid-water region or upper layers of the waters. Demersal fish live in deep water or near the bottom of the ocean. Pelagic fish are of two types: coastal and oceanic. Coastal pelagic fish live in shallow regions or water above the continental shelf. Oceanic pelagic fish live in deep waters of the ocean beyond the continental shelf. Demersal fish are also of two types: benthic and benthopelagic. Benthic fish rest on the ocean floor, whereas benthopelagic fish float in water just above the ocean floor. Thus, this summarizes the difference between pelagic and demersal fish.

Reference:

1. “Contributions of Pelagic and Demersal Fish.” FAO.org.
2. “Demersal Fish.” Wikipedia, Wikimedia Foundation.

Image Courtesy:

1. “Moofushi Kandu fish” By Bruno de Giusti – Own work (CC BY-SA 2.5 it) via Commons Wikimedia
2. “Taeniura lymma 2” By Jacek Madejski – sent by mail to User:Ark with permission (CC BY-SA 3.0) via Commons Wikimedia