The Climbing Perch: An Air-Breathing Fish

The climbing perch (Anabas testudineus) is a hardy freshwater fish native to South and Southeast Asia, including India, Bangladesh, Myanmar, Thailand, Malaysia, and Indonesia. Though small and plain in appearance, it is well known for its exceptional ability to survive in harsh, changing environments such as ponds, rice fields, and swamps.

One of its most remarkable features is the labyrinth organ, a specialized respiratory structure above the gills that enables it to breathe atmospheric oxygen. When dissolved oxygen levels are low, the fish regularly surfaces to gulp air, extracting oxygen efficiently. This adaptation allows it to survive in stagnant, oxygen-poor waters and even remain alive out of water for several days, provided its body stays moist and cool. By supplementing gill respiration with air-breathing, the climbing perch gains a significant survival advantage in unpredictable tropical habitats.

The climbing perch is also famous for its ability to move across land, a behavior often described as “walking.” When ponds dry up or conditions deteriorate, it migrates to new habitats using its strong pectoral fins and sharp opercular spines (gill covers) to push forward while its body wriggles. Although early reports exaggerated its ability to climb trees, it cannot scale vertical surfaces. However, it can travel across wet soil, grass, and uneven terrain, especially during humid nights or rainfall, when dehydration risk is reduced. This unusual mobility helps it colonize nearby water bodies effectively in seasonal landscapes.

The species is omnivorous, feeding on insects, small crustaceans, zooplankton, plant material, and organic debris, which supports its adaptability in varied environments. It breeds in shallow waters during warm rainy seasons, releasing eggs among submerged vegetation where larvae hatch quickly. This rapid life cycle helps populations recover after droughts or habitat disruption. In many parts of Asia, it is also an important food fish, valued for its resilience during transport and its firm flesh. However, its hardiness has led to it becoming invasive in some regions outside its native range, where it can compete with local species and alter aquatic ecosystems.

Overall, the climbing perch is a striking example of evolutionary adaptation among freshwater fishes. Its ability to breathe air, survive land exposure, and exploit diverse food sources has allowed it to thrive in unstable environments. These traits make it both an ecological survivor and a subject of scientific interest in adaptive biology. It continues to be studied for insights into resilience in changing climates worldwide and environmental adaptation research.
The Climbing Perch: An Air-Breathing Fish

Freshwater mussels

Shellfish is divided into two categories: mollusks and crustacean. Mollusks are surrounded either wholly or partially by a hard shell. Common types include clams, oysters, scallops and mussels.

The phylum Mollusca includes approximately 90000 species with a wide array of body size, shapes and forms. Freshwater mussels are aquatic mollusks with edible soft tissues and hard, calcareous shells.

Freshwater mussels are a conspicuous and important element of aquatic ecosystems in much of North America and throughout the world. Mussels are bivalve mollusks and are built much like marine bivalves.

Mussels are less often consumed raw but occasionally are eaten raw in some regions. In the United States, many state regulatory agencies require that consumer health risk notices be present on restaurant menus and consumption risk warning signs be prominently displayed at retail outlets.
Freshwater mussels

Fish of Arowana

Arowana is family of Osteoglossidae fresh water fish that have a bony tongue, slender body with large scales and a pair of barbels on the tip of the lower jaw.

The arowana is a mouth brooder. After the eggs hatch, the male scoops the tiny larvae into his mouth to protect them. Arowana is well-known predatory South American species that is commonly kept in large aquaria.

Osteoglossum bicirrhosum

This fish dorsal and anal fin located posteriorly for a heavy thrust, and the arowana has a surface-oriented jaw. The silver arowana (Osteoglossum bicirrhosum) in Amazon also is known as ‘monkey fish’ because it can jump out of the water to catch prey.

If there is one very popular breed among Arowanas, it is probably the Asian Arowana. This extraordinary fish belongs to the Scleropages family and it is one of the varieties of large freshwater fish found in some rivers and lakes of Southeast Asia.

The arowana is an endangered species of fish that is protected under the UN Convention of International Trade in Endangered Species of Wild Fauna and Flora. An arowana caught in the wild cannot be sold.
Fish of Arowana

Freshwater fish of common carp

Common carp or Cyprinus carpio is one of the largest members of the minnow family and close relative of the goldfish. It is a truly domesticated fish species. North American carp originate from pond-cultured carp brought from Great Britain during the 19th century. It has escaped into wild and became an invasive exotic that kills aquatic vegetation.

The common carp has a deep body form and a heavy appearance. Distinctive features include a short head, a rounded snout, a single long dorsal fin, a forked tail, and relatively large scales.

Crucian carp

The common carp is a widely cultured strictly freshwater fish which can reach a length of about 80 cm and weight of about 10 to 15 kg.

Common carp reproductive potential is enormous. A large female may lay up to two millions eggs in one season. The eggs normally are deposited over vegetation to which they adhere.

Carp are usually mature after about 2 years and a weigh of 2 to 3 kg.  Growth rate is high in the tropics where the fish can reach a weight of 400 to 500 g in 6 months.

Common carp are found in slow-moving or still waters ranging from streams and ponds to large rivers and lakes. They can be found over all substrates but prefer shallow water with soft substrates for feeding.
Freshwater fish of common carp

Freshwater fish

Despite their enormous ability to adapt to a wide range of aquatic environments, fish are far from being uniformly distributed in the waters of the globe.

Thus 41 percent of all fish species are found exclusively in fresh water even though fresh water covers only about 1 percent of the earth’s surface.

Most of freshwater is locked in polar ice caps, stored in underground aquifers or part of soil moisture and permafrost. Only 0.01% of earth’s water is available as freshwater in rivers and lakes.

The distribution of freshwater fishes is often more distinct and restricted than that of amphibious and terrestrial animals.

Besides the physical limits of water bodies, there are factors that govern the distributions of fishes within the systems themselves.

Among these are physical barriers, physicochemical tolerance, ecological barriers and biological and behavioral factors.

Fishes are classified as either primary or secondary freshwater species, based on their tolerance to salinity. 

Primary freshwater species have no or very low tolerance to saltwater.

Secondary freshwater species are tolerant to saltwater and as such, have a greater potential for dispersal along stretches of coast devoid of freshwater outlets.
Freshwater fish

Catfish

Catfish once viewed disdained fully as the scavenger of fish, has now become a high ranking choice of connoisseurs. It is low in fat, cholesterol and calories perfect for those who are watching what they eat.

Catfish comprise an incredibly large and diverse group of animals much larger, in fact than most people realize. One in four species of all freshwater fishes is a catfish.

Most catfish are found in fresh water, although there are two families that contain saltwater species.

Many of the world’s significant river systems are home to at least one species of catfish, and in most cases these fish rank among the largest fish of the river system.

There is little finesse in angling for any of the catfish. They love in deep holes, often in turbid water, and their diet is unsophisticated, as they use eight sense barbells to locate foods.

Most catfish prefer the sluggish localities of lakes and rivers; some do best in fairly swift waters.

Catfish