The Motoro Ray

Potamotrygon motoro is a freshwater stingray that belongs to the potamotrygonidae family. It's distribution is thorough South America and includes Uruguay, Paraná-Paraguay, Orinoco, and Amazon River basins. It gets to about 39 inches and requires a large tank when adult. They thrive in a PH of 5.0 to 6.0 and a DH no greater than 10. Since they are from a tropical climate, they do best in temperatures of 75 - 78° F.

They are make fine aquarium specimens as long as you keep the water parameters right and have enough filtration. Since they get quite large, when selecting a tank for them, give more importance to bottom area than depth, this is where the rays will spend most of their time.

The motoro ray is the most commonly bred species of stingray, it is also the most popular stingray in the ornamental fish trade. This species can reach sexual maturity at a relatively small size, around 12 inches. Because of this is that the motoro is more easily bred in the home aquarium than any other species of stingray that reach maturity at 18 inches or bigger.

An important consideration to keep in mind is that all freshwater stingray species can grow to a large size when full grown. A freshwater stingray aquarium should never be smaller than 50 gallons, since they will soon outgrow smaller aquariums. The rate growth for freshwater stingrays depends on how often and how much they are fed and on water quality. When kept in a well maintained aquarium with optimal food, a freshwater stingray will reach maturity in about 3 years.

The Antenna Ray

Plesiotrygon iwamae is a freshwater stingray, commonly known as the Antenna Ray, they are the only member of the genus Pleisotrygon. They belong to the family Potamotrygonidae and to the class Elasmobranchii, which is what sharks belong to. They get to about 22 inches in length, this does not include the tail. Their distributionis the upper to lower Amazon River basin, from Ecuador to Belém, Brazil, in the Napo, Solimões, Amazonas and Pará rivers.

Antenna rays have smaller mouths than most other rays. Because of this, they feed on black worms, or tubifex worms. When young (under 10 inches) this species has trouble eating even the smallest night crawlers so blood worms would be better. Larger specimens will eat earth worms, chopped squid or even small feeder fish. The tail of the Antenna ray is really delicate and a newly imported specimen with a damaged tail is more likely to die. If its a small injury towards the end of the tail there are good chances it will heal but if it's near the base of the tail, it rarely heals and eventually falls off; once this happens, the ray will die. The cause of the death will probably be due to a bacterial infection entering the blood stream through the broken tail.
Such injuries usually happen in transit but in the aquarium are also likely to happen. Intake tubes or powerheads are often the cause but netting the fish is also dangerous for them, since the tail can get stuck in the net.
This group is best kept in a tank without ornamentation, bulky equipment or other fish. Gravel substrates are ok for this species but young ones should be kept in bare-bottom tanks to make feeding easier.

There is a type of Antenna Ray called a "Black Tailed Antenna Ray". This type seems to be less sensitive to tail injuries than the common antenna ray. This is the only species of Freshwater Stingray that commonly rests with its disc margin elevated off the substrate when in good health. (Do not confuse with "death curl").
The reason for them to hold their disc in such ways is not known.

The Black Tailed Antenna Ray is a dwarf stingray and even when adult has trouble eating anything larger than black worms, blood worms or tubifex. If you feed live worms, before feeding stir the substrate a little bit to make sure any survivor worms are eaten before they colonize your tank.

The Freshwater Stingray

One of my favorite aquarium fish is the freshwater stingray, particularly the ones of the genus Potamotrygon. This fish is not for the beginning hobbyist but if you have some experience this is a fascinating animal. There are many species of stingrays in the wild but you will find just a few species for sale in any local fish store. You can get a wider choice of species from specialized breeders online but they are sold by their common names. Because of this, I will not use the scientific names in this article.

Stingrays are very sensitive to water parameters. They have relatively large kidneys and they produce a lot of ammonia, so make sure you have adequate filtration. The type of aquarium you keep them in very important since they stay at the bottom nearly all the time, a tank with a large bottom area is the best, instead of a taller more narrow tank. Rays get quite large so a tank for an adult specimen must be at least 4 feet by 2 feet, the height can be 2 feet. They are from tropical locations and should have a temperature of around 75° to 80° F. The PH must be maintained at a range between 6.5 to 6.75 and keep the TDS (Total Dissolved Solids) below 200.

When buying a new Stingray, stay away from the specimens that have a "curled" disc,this is called the "death curl" since any stingray showing it will surely die soon. A healthy ray always keeps the disc margin flat to the substrate, except when actively moving about the tank. Some people speculate that this is due to kidney failure from over exposing the animal to high levels of ammonia (like when in transit). Other possible signs of sickness are:
- a cloudy or milky film covering the body
- rapid breathing or panting while at rest
- open sores
- showing the pelvic bones, rays in good health should not show this bones.

Make sure its legal to keep Stingrays in your state, some require special permits and some times they are restricted to educational or research facilities. Here is a list of the restricted states:
Arizona
Arkansas
California
Florida
Georgia
Hawaii
Nevada
Oklahoma
Texas
Utah

This is a general guide to classify Stingrays:

Large-Eyed
Black Rays
Tiger Ray
Motoro Ray
Mantilla Ray
Otorongo Ray
Chocolate Ray
There are a number of Rays being sold as "Teacup" rays while this should be used to determine the size of the ray.

Small-Eyed Rays
China Ray
Antenna Ray
Coly Ray
Ceja Ray
Manzana Ray

Be wary when considering good tank-mates for these fish. Stingrays are usually not aggressive towards bigger fish but don't mix them with something they can eat since I have lost a few tetras, shrimp and even some cory catfishes. In the other hand I have had plecos that attach themselves to the rays, mostly annoying them but in some cases injuring them.

Feeding is probably the trickest part of keeping ray. When you first buy them is sometimes hard to get them to start eating and here is when I have lost most of my rays. I have found that they like squid, earth worms (still wriggling) and raw red meat. Feed them at least twice per day.

Next I'll talk about sexing and breeding Rays...