Rhamphichthys
From Wikipedia, the free encyclopedia
| Rhamphichthys | |
|---|---|
 | |
| Rhamphichthys marmoratus | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Gymnotiformes |
| Family: | Rhamphichthyidae |
| Genus: | Rhamphichthys J. P. Müller & Troschel, 1846[1] |
| Type species | |
| Gymnotus rostratus | |
Rhamphichthys is a genus of freshwater ray-finned fish belonging to the family Rhamphichthyidae, the sand knifefishes.[1] These fish are eel shaped (or anguiform) with a distinct beak like snout which gave them their name.[2] Like most other knifefish Rhamphichthys species have electrical organs that help them live in the murky waters of South America.[3]
Rhamphichthys combines the Greek rhámphos (ῥάμφος), meaning "beak" or "bill" and ichthýs (ἰχθύς), which means "fish". This is a reference to the snout forming a tube in these fishes.[4]
Species
Rhamphichthys contains the following valid species:[5]
- Rhamphichthys apurensis (Fernández-Yépez, 1968)
- Rhamphichthys drepanium Triques, 1999
- Rhamphichthys hahni (Meinken, 1937)
- Rhamphichthys heleios Carvalho & Albert, 2015
- Rhamphichthys lineatus Castelnau, 1855
- Rhamphichthys pantherinus Castelnau, 1855
- Rhamphichthys rostratus (Linnaeus, 1766)
Range and habitat
All species within Rhamphichthys can be found in the major river systems of South America, notably the Amazon basin, Orinoco River, Río de la Plata, and the Paraná River.[6] They have been found in pools created during the rainy season then become isolated as the waters recede. They prefer to stay near the bottom of soft bottom rivers near steep banks with lots of vegetation.[2][7][6] These waters are usually extremely murky and full of silt deposits which makes sight difficult, perfect for organisms that can detect their surroundings with weak electric signals.
Characteristics and biology
The sand knifefishes are characterized by their elongated bill-like snout and elongated eel-like body. On average they will reach between 26.5 and 100 cm in length.[6] They have a long anal fin that starts just behind their small pectoral fins and end almost at the end of the body. Their caudal or tail fin is either highly reduced or missing (depending on the species). All species lack both dorsal and pelvic fins but do have a dorsal ridge down the center of their back.[2] They also have very small eyes, not relying on sight to find food or detect other organisms. Coloration varies between species, but all seem to have highly mottles coloration with a lighter base color on the belly (or venter) and darker colors on the back (or dorsum). The spots seem to be larger on the back and get smaller as they move down to the underside.[6] Some individuals seem to have a blue tint to their anal fin, but it is not yet understood if that is characteristic of a species or not. Internally they have highly reduced gill rakers, a large stomach, and an anteriorly positioned anus which lies directly under the pectoral fins.[2]
Not much is known about their behavior and biology. They are opportunistic predators feeding predominately on invertebrates such as insects and crustaceans dug up from the sandy river bottoms, but seem to eat small fish as well.[8] They seem to keep to a relatively small home range and are solitary except while breeding. They use their electrical organs to identify prey, competitors, mates, and possible predators.[3] It is thought they mate during the dry season when waters are warm and low.
