ATHERENIFORMES - the silversides


Belonidae
A mainly marine family, they are represented in Amazonia by needle fish of the genus Potamorrhaphis. These are long and slender with greatly elongated jaws. They normally hunt in schools close to the surface of open water in floodplain lakes. They feed on small insects and other animals caught on the surface. These shy fish are abundant in all white water lakes and are easily spotted, however, they will quickly swim away if your shadow should fall over them.

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Potamorrhaphis guianensis - Lateral view of specimens caught in Lago Mamiraua. Note the lack of caudal fin (tail) probably caused by piranha attack
Potamorrhaphis guianensis - Lateral view of specimens caught in Lago Mamiraua. Note the lack of caudal fin (tail) probably caused by piranha attack.

Close up of the head of Potamorrhaphis guianensis showing the extended jaws
Close up of the head of Potamorrhaphis guianensis showing the extended jaws

Potamorrhaphis guianensis hunting as a group close to the surface of a white water floodplain lake
Potamorrhaphis guianensis hunting as a group close to the surface of a white water floodplain lake


Cyprinodontidae
A large, widely distributed family of small, mostly freshwater fish. The head is flattened and the mouth terminal and wide. They often hunt at the water surface. The scales are relatively large. The only genus found in the floodplain is Rivulus whose members are common in floating meadow. These small fish are abundant in forest streams.

Rivulidae
(Rivulidae is a recently formed family presumably as part of an attempt to break up the very large Cyprinodontidae.)
Identification The only species of Rivulus recorded from litter-banks within the Tarumã-Mirim. Characterized by the large eyes set high on the head to look upwards. The fins are adapted for moving over surfaces and the spines are almost finger-like.
Colour: In life almost transparent with brown markings. Preserved, white with brown/black markings. N.B. I am not sure to which species our specimens are referable, but I think it is known.
Habitat: At the water's edge in litter-banks.
Abundance: Common but never found in large numbers.
Food: Unknown
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Lateral view of a Rivulus species
Lateral view of a Rivulus species