45 ANIMALS THAT BREATHE THROUGH GILLS - BIOLOGY - 2025

The animals that breathe through the gills are those that have specialized organs called gills or gills that allow them to carry out the respiratory process in the aqueous environment in which they live.

These animals include fish, some reptiles early in life, most mollusks, crustaceans (although some have tracheal respiration), and some annelids and zoophytes.

The gills vary in structure from animal to animal. They range from simple filamentous epithelial structures to complex structures comprising hundreds of lamellae enclosed in a cavity or branchial chamber.

They have multiple blood vessels and are continuously permeated by water flows, which makes gas exchange between water and blood possible.

Examples of animals that breathe through gills

1- Frog

Like other amphibians, the frog exhibits gill respiration in the early stages of its life cycle.

The gills allow it to breathe in water during its period as a larva and tadpole. When reaching adulthood, the gills disappear, then it happens to have a cutaneous and pulmonary respiration.

2- Octopus

Octopuses are part of the cephalopod mollusks, studied by malacology

Image by edmondlafoto from Pixabay

The octopus is a cephalopod mollusk with gill respiration. The octopus has three hearts. Two of the hearts are housed near the base of the gills and they are responsible for directing the blood to the gills where gas exchange takes place.

Carbon dioxide is released and oxygen is obtained. The third heart is responsible for pumping oxygen-rich blood to all tissues of the animal.

3- Clam

The clam has two pairs of gills, which are very delicate structures formed by ciliated sheets that allow gas exchange in an efficient way.

A particular characteristic in these animals is that the gills also fulfill functions of osmotic regulation, excretion and digestion.

4- Shark

The shark's respiratory system is made up of gills or gills of cartilaginous tissue from which gill filaments are detached. These open and close to allow the passage of water and carry out the gas exchange.

5- Manta ray

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Manta rays, like sharks, have a cartilaginous gill structure. This is located in the lower part of the body, near the base of its dorsal fins.

6- Calliostoma annulatum

This sea snail, characteristic for the beauty of its shell, lives in the kelp forests of the reefs. The gill is located in the cavity of the mantle in front of the heart.

7- Sea hare

It is a mollusk that can measure up to 20 cm. His body is elongated and muscular and folds emerge from him that completely embroider it.

Young specimens are carmine red and as they age they turn brownish-green with small spots. The gills are located on the right side of the head.

8- Tent

Carp is a freshwater fish native to Asia, but it is currently scattered throughout most of the world. Like other fish, its respiration is gill.

9- Scalar fish

It is a freshwater fish with a flattened body and a triangular shape. It is characteristic for the size of its dorsal and anal fins that accentuate its triangular shape. As in the case of all fish, their respiration is gill.

10- Australian lungfish

It is a fish that belongs to the group of lungfish. These are fish that have lungs, in addition to their gills and that under certain environmental conditions can survive out of the water by breathing the oxygen found in the air.

The body of the Australian lungfish is elongated, its head is small and flattened and the end of its tail is pointed.

11- Protopter or African lungfish

This fish, like the Australian lungfish, has the ability to survive long periods out of water thanks to its double breathing system: gill and lung.

It is a fish with a long and muscular body and a small, pointed head. It survives the months of drought by burying itself in the mud, where it remains wrapped in a layer of mucus that it secretes.

12- Lepidosiren

It is another fish belonging to the group of lungfish typical of South America. Of the group of lungfish, it is the fish that presents greater dependence on air oxygen than on aqueous oxygen. Only 2% of its oxygen requirement is obtained through its gills.

In the dry stages, the lepidosiren digs a cave in the mud in which it buries itself and which it covers with a plug of mud with holes that allow it to take oxygen from the surface. Its body is elongated and thick, similar to that of eels.

13- Sardines

14- Shrimp

15- Whale shark

16- catfish

17- Seahorse

18- Toads

19- Axolotl

20- Prawns

21- Lobster

22- Tuna

23- Salamanders

24- Chunerpeton

25- Mixino

26- Lampreys

27- Sawfish

28- Electric Stripe

29- Yeti Crab

30- Coquina

31- Turbot

32- Sepia

33- Clown fish

34- Coquina

35- Silverside

36- Marine Worm

37- Newt larvae

38- Golden

39- Marine polychaete

40- spider fish

41- Dule water snail

42- Ciprea tiger

43- Vampire Squid

44- Slugs

45- Aquatic mealybug

Types of Gills

External gills

These are simple and primitive structures that develop as hollow outgrowths from the body wall. In echinoderms, these types of gills vary in appearance.

In some species such as starfish they appear as papilliform structures, while in sea urchins they are gill-shaped. In these animals, the gills work together with the tubular structures (tracheae) to carry out the respiratory function of gas exchange.

In annelids the respiratory process is usually carried out through the skin. However, some have additional gills. In some polychaetes there are highly vascularized gills attached to the notopodium.

In the arenicola, a burrowing polychaete, and ozobranchus, a leech, the gills or gills are branched tufts arranged segmentally and in pairs along the body. The tentacles of sabellids and snakes are also considered gill-like respiratory structures.

Among vertebrates, gills are present in the larvae of frogs (tadpoles) or as a neotenic feature of some adult salamanders (axolotl, Necturus). Some fish also have external gills during the larval stage (elasmobranchs, lungfish).

Protopteran and lepidosiren larvae have four pairs of external gills early in their lives which are replaced by internal gills when the operculum develops.

Internal gills

Obviously the external gills have disadvantages. They can become obstacles during locomotion and are a source of attraction for predators.

For this reason, in most gill-breathing animals, the gills are located in partially closed chambers that provide protection for these delicate structures.

One of the main advantages of internal gills is that they allow the continuous flow of running water to ventilate the gill chambers. Furthermore, this arrangement of the gills allows the animal's body to be more streamlined.

In bivalves, tunicates, and some echinoderms, ciliary activity is responsible for the circulation of water through the branchial chamber. The animals receive their oxygen requirements and also their food supplies from the circulating water.

In crustaceans, several types of well-developed internal gill structures are observed. In these animals, the gills are made of vascularized laminar structures.

In the case of gastropod molluscs, the gills are located within the cavity of the mantle which receives continuous water currents.

How branchial respiration occurs

Aquatic vertebrates have developed very efficient gill respiration. The gills are located in a chamber known as the opercular chamber. The oral cavity sucks water which is forced back through the gills to exit through the opercular cavity.

This flow of water over the respiratory epithelium is continuous and the respiratory current is produced by muscular movements which pump the water. This occurs thanks to a double pump mechanism that operates simultaneously.

On the one hand, the oral cavity functions as a pressure pump that forces water through the gills, while on the other, the opercular suction pump moves water through them.

The oral cavity and the opercular opening are protected by valves that remain static, but that move according to the degree of pressure exerted on them.

In many aquatic animals, especially fish, an important characteristic is that the flow of water through the gills is in only one direction and the flow of blood in the opposite direction. This is called the countercurrent principle and ensures a constant degree of oxygen tension between the water and the blood.

References

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