Red Bellied- Pirhanas ( Pygocentrus nattereri )
The red bellied piranha has the reputation for being one of the most ferocious freshwater fish in the world. They have a set of razor sharp teeth which are capable of stripping flesh from prey and dead animals. As their name suggests, they have a reddish tinge to the belly when fully grown, although juveniles are a silver color with darker spots. They grow to a maximum length of 33 cm and a weight of 3.5 kg.
Distribution.
Red bellied piranhas live in the Amazon river basin, coastal rivers of north eastern Brazil , the basin of Paraguay, Parana and Essequibo river. Recently Pirhana was caught in the Catawba river in north Carolina . Pirhana have also been discovered in Kaptai lake in south east of Bangladesh.
Pirhana- biology
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The Piranhas body shape is high-backed and more or less stocky indicating that they live in slow-flowing waters. The head is large with a steep profile. A reliable differentiation of the sexes tends to be extremely difficult.
The fins in combination with the air bladder enable the fish to control all movements. .
When the Piranha stands still it uses the pectoral fins to neutralize the 'jet effect' that the gills produce. The dorsal fin can also be used to this task. The dorsal fin can in addition be used to put the Piranha in reverse. At high speeds the only significant fin is the tail fin, the other fins are folded close to the body.
Teeth
Piranhas are world-famous for their razor-sharp teeth. Native peoples of South America will catch the piranha and use their teeth to make tools and weapons. Even the fishermen who catch these vicious little predators have to be careful when the fish is out of water. A single piranha out of water is still dangerous enough to take off the flesh, or the odd toe, from an unwary fisherman
Lateral Line
The lateral line is a special sense organ situated along the sides of the fish. It can be seen as a thin line from head to tail. It detects pressure canges in the water and enables the fish to recognize art friends by their unique swim frequency. Sick fish can also be detected. And in the whitewater rivers, where the visibility is poor, the Piranhas can use the lateral line to navigate and avoid rocks and similar obstacles.
Smell
Many authors have mentioned the incredible smell possessed by sharks. Piranhas too have an extraordinary sense of smell.
Hearing
Experiments with bony fishes have resulted in the conclusion that their hearing was excellent. Since Piranhas themselves produce sound, using the air bladder as a resonator, it is assumed that they, as well, can hear well.
Eyes
The relatively large eyes of the piranha have a hard, spherical lens that does not change shape. The eye is perfectly adapted for close-up vision, and is short-sighted at rest. Of course it can be adapted for grater distances. This is achieved by the lens being displaced by the lens muscle.
The position of the eyes makes the visual field very large (se illustration above), and makes a narrow field of stereoscopic vision.
Tests have shown that fisheyes similar to those of the Piranha can distinguish between 20 different colors between 370 and 700 nm
How piranhas attack
The piranha is renownedly portrayed and known as a vicious species of fish hunting in large schools.
From the moment tiny baby piranhas hatch from their microscopic eggs, they come into the world armed and dangerous. Baby piranha will feast on tiny crustaceans, fruits, seeds, and aquatic plants. Once they reach about 1.5 inches in length they begin feeding on the fins and flesh of other fish that wander too closely. As they grow larger they begin to venture out in groups (schools) of about 20 fish where they use a variety of hunting strategies to kill and eat their prey. The interesting part is they don't kill their prey first, they just start eating the victim alive - that's what makes them so ferocious. Adult piranha have been known to eat their own babies.!
When a school of piranha are in a feeding frenzy the water appears to boil and churn red with blood. They attack with such ferocity that they strip an animal of its flesh within a matter of minutes, even taking bites out of each other in the process.
Piranhas are ecologically important:
Ecologically, piranhas are important components of their native environments. these fishes are widespread and inhabit diverse habitats within both lotic and lentic environments.As both predators and scavengers, piranhas influence the local distribution and composition of fish assemblages.
Adult piranha will eat just about anything - other fish, sick and weakened cattle, even parts of people. Sickly cattle that have stooped their heads down to drink from the river have been grabbed by the mouth and nose and pulled into the water, completely devoured minutes later. As wicked as it all sounds, piranhas have a useful function in the Amazonian jungles just like any other predators in the wild. They are part of the checks and balances Mother Nature employs to eliminate the weak and sick so only the strong survive.
