20 October 2008

Piramboia - Evolutionary link between air and water breathers in the Amazon

There’s a very unusual fish in the Amazon that could be the closest ancestor to the first air-breathing life forms on Earth. The South American lungfish, also known as the Piramboia (Lepidosiren paradoxa), is the one obligate air breather that can actually survive outside of water due to its efficient oxygen breathing system. This wonderful fish resembles a mix between a ghost fish and an eel. It has very dark grey to black skin that has a very leathery appearance, tiny eyes like an eel, and its body spreads out in its anterior portion. It can reach over 3 feet long.

The Piramboia seeks slow moving waters and it can usually be seen sitting on the bottom of the shallow ridges around the Amazon River. It rises occasionally to suck in air, only to return to its comfortable nest on the floor of the river. The Piramboia will hunt for insects, snails, berries and shrimp using suction feeding. Unlike other fish in the Amazon, the lungfish can survive on meat and vegetable matter, making it one of the few omnivorous fish.

 The dry season is not a problem for most Piramboia. While other fish struggle with the lack of oxygen in the Amazon River, the Piramboia will burrow into the soft mud at the bottom of the Amazon and wait out the rest of the season. Their metabolism slows and they don’t leave their burrow. The hole can go underground a few inches, and can dry out completely before the rainy season starts again in the Amazon. The Piramboia breathes in air during this dry time, and most survive in their burrows safe from predators. The biggest danger to these novel fish are giant river otters, which know how to dig for them during the dry season.

During the rainy season, the Piramboia will begin mating as the water rises and fresh water flows into the Amazon area. Male and female Piramboia create a burrow-like nest in the muddy bottom. They lay quite a few eggs, and the male guards them voraciously. Upon hatching the fry look like tadpoles and breathe through gill-like structures. The male also develops extra capillaries in his pectoral fins, and will fan the fry to provide more oxygen and remove carbon dioxide. At around 8 weeks the fry develop their lungs and are able to breathe air like their parents.

At first, young lungfish eat mosquito larvae, snails and algae. As they mature, they become adept at catching shrimp and even small fish such as tetras. Whether or not the juvenile lungfish survive to their first dry season is a big factor in whether or not they survive to adulthood. After they have survived one dry season, most of them will grow to full size.

The Piramboia is the only species of fish in the Amazon to possess a true lung structure that allows them to breathe air without the aid of water. The only time the Piramboia don’t breath through their lungs is when they are breeding. At this stage in their lives, they rely on extra capillaries in their pectoral region and their gills.

Unfortunately, much remains unknown about this rare, unique fish. Breeding in captivity has never been accomplished, and there are quite a few people who keep aquarium specimens.

Lungfish are escape artists. If a lungfish is in an aquarium, it will try to escape and if it does, it will survive and find its way around the house and hide.

Locals don’t catch lungfish for food, and most encounters with these oddballs are during the dry seasons. Local children and pets often find the burrows of these fish and attempt to dig them up. Since the fish are hibernating, they are vulnerable. Otters can usually find their burrows as well, and will help themselves to an easy meal if they can dig the lungfish from its nest.

Because of their special lungs, Piramboia are high interest specimens for evolutionary biologists, as they may hold the unknown evolutionary link between fish and air-breathers. Scientists are still studying this fish to discover what genetic features have survived and evolved into the mammals of today.

Photos copyright: Fishbase.org and Wikipedia.org


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