What is the Difference Between Holobranch and Hemibranch

The main difference between holobranch and hemibranch is that holobranch is a pair of series of filaments in the respiratory tissue in the gills, whereas hemibranch is one series of filaments in the respiratory tissue in the gills.

Gills are structures in aquatic organisms that help in respiration. They are mostly found in fish. Moreover, gills have complex structures with modifications and adaptations to bring about the respiration process efficiently.

Key Areas Covered

1. What is a Holobranch
     – Definition, Filaments, Features
2. What is a Hemibranch
     – Definition, Filaments, Features
3. Similarities – Holobranch and Hemibranch
     – Outline of Common Features
4. Difference Between Holobranch and Hemibranch
     – Comparison of Key Differences

Key Terms

Hemibranch, Holobranch

What is a Holobranch

Holobranch is a gill with a row of filaments on each side of the branchial arc. They are a type of gill structure present in certain aquatic animals, specifically in the class of cartilaginous fish. Examples of fishes having holobranchs include skates, sharks, and rays. A holobranch is often referred to as a complete gill. The arches the gills contain are bony or cartilaginous. Moreover, the anterior and posterior parts of each gill arch possess plate-like gill filaments. A complete gill (holobranch) consists of both anterior (oral) and posterior(aboral) hemibranchs. The holobranch structure consists of a central stem or axis. From this axis, many secondary branches arise. Each of these secondary branches gives rise to a large number of tertiary branches. This branching pattern thus results in a complex 3-dimensional structure. This branching pattern is also repeated in each filament. Furthermore, this arrangement increases the surface area of the gills.

Function of Holobranchs

Aquatic organisms, especially cartilaginous fish, have high metabolic rates. They should have a constant supply of oxygen to perform metabolic activities even at low oxygen levels. Hence, they need to extract oxygen at a very high rate efficiently. The main function of the holobranch is to extract oxygen from water and release carbon dioxide, which is a waste product of metabolism. Furthermore, holobranchs facilitate the extraction of oxygen from water efficiently. In fact, some species extract more than 90% of the available oxygen with the help of holobranchs. Holobranchs are specialized structures that have evolved as a result of being subjected to many different challenges faced by aquatic organisms.

Holobranchs also help to regulate the water balance and ion balance in the body of fish. The gill filaments have specialized cells lining them, which play a role in transporting chloride, calcium, and sodium actively. This active transportation helps in maintaining the required concentrations of ions in the body fluids, which is essential for many different physiological functions, such as maintaining proper pH levels and conduction of nerves.

What is a Hemibranch

A hemibranch is one of the two arch-shaped structures forming a fish’s gill. This is a structure with a single layer of filaments. A combination of two such hemibranchs forms a complete gill. Therefore, we can consider a hemibranch as half of a gill. Each hemibranch contains both primary and secondary lamellae. The primary gill filaments remain separated from the branchial septum at their distal end, making two hemibranchs in opposition, which allows the water to flow between the gill filaments.

Gill filaments take the shape of a blade. They are supported by gill rays. Ligaments connect the heads of the gill rays of both hemibranchs. They also have two types of adductor muscle units in teleosts. The primary epithelium is the epithelium lining the gill filaments. Moreover, there are two parts in the epithelium: glandular and non-glandular. Generally, the structure associated with hemibranchs increases the surface area in contact with water, which facilitates the maximum absorption of oxygen needed for the body of aquatic organisms.

Similarities Between Holobranch and Hemibranch

• Holobranch and hemibranch are words people use to describe fish’s gills.
• Holobranch is a complete gill, while a hemibranch is half of a gill.

Difference Between Holobranch and Hemibranch

Definition

Holobranch is a pair of series of filaments in the respiratory tissue in gills, whereas hemibranch is one series of filaments in the respiratory tissue in gills.

Nature

In simple words, a holobranch is a complete gill, while a hemibranch is half of a gill.

Filaments

Holobranch has twice the filament number of a hemibranch.

Conclusion

In brief, gills are the structures present in some aquatic organisms for the process of respiration. The main difference between holobranch and hemibranch is that a holobranch is a pair of series of filaments in the respiratory tissue in the gills, whereas a hemibranch is one series of filaments in the respiratory tissue in the gills.

Reference:

1. “C. Gill Structure.” Online Fish Physiology. The University of Tennessee, Knoxville.

Image Courtesy:

1. “Fish gill respiration” By Користувач:Shao / Anaxibia (CC BY-SA 3.0) via Commons Wikimedia
2. “Fish gill structure” By Користувач:Shao \ Anaxibia (CC BY 3.0) via Commons Wikimedia