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David Webber
80 Varick Street #3C
NY NY 10013
USA

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An Introduction to Freshwater Stingrays

By David Webber (www.freshwaterstingray.com)
(No photographs may be used without the author's written consent)

Aquarticles

The author with a few of his stingrays

In the last few years freshwater rays have become increasingly available and popular and tanks have become larger and cheaper, making them a reasonable pet for the dedicated home aquarist. Although some other major rivers around the world have ray populations, most freshwater ray species are found in Amazonia, and as with its other flora and fauna, the Amazon system has an abundance of ray variants found all along the river and in many of its tributaries, from Peru and Colombia in the West to the mouth of the Amazon in North Eastern Brazil. Some ray species are also found in other tropical South American rivers with no direct connection to the Amazon. Stingrays are very ancient species, tracing their evolutionary history as far back as 300 million years.

Evolutionary History

The most commonly found species in South American rivers are Potamotrygon. There are also rays known as China or Coly rays, about which little is known at this time.

P. motoro - Peru

Large China Ray middle, P. leopoldi top, P. motoro bottom

Estrella Ray center, Peru

It is thought that all of these Amazon rays are most closely related to Pacific Marine rays. Their isolation would have occurred when the Andes Mountains rapidly rose up about 15 million years ago, blocking the Westward flow of the river as it then was and forcing it to flow east all the way to the Atlantic, trapping many rays in the new system. This isolation and the Amazon’s tropical climate and seasonal massive changes in water levels created ideal circumstances and great pressure for evolutionary changes, as represented by the huge variety of stingrays found in just the one system. Even individual species that are found along the whole river, such as Motoros and Histrix, are polymorphic, each exhibiting their own wide range of colors and patterns as habitat and available diet change subtly between regions.

Scobina Ray

Flower Ray from Venezuela/Columbia

A word of warning about a stingray's stinger

Stingrays are so-called for their serrated, dagger-like stinger located on the top of and lying flat towards the end of the tail. Usually sheathed in a layer of skin and not always easy to see, this effective defense weapon is made of a protein complex , and is accompanied by a nasty venom usually released when the skin sheath of the stinger is ruptured. If the stinger cuts you it can cause large local blisters and intense burning throbbing pain. The immediate treatment for this is to immerse the wound in water as hot as can be tolerated, which helps to neutralize the toxins. This is not always possible, especially on the river. The traditional first aid treatment there is to urinate on the wound which works because urine is both hot , sterile and slightly acidic. Amazon folklore says that it must be a virgin who pees on the wound, leading to the joke 'there is good news and bad news......there are no virgins in Brazil'. Although extremely painful the ‘sting’ is rarely fatal unless by some bizarre accident it is in the chest near the heart, a tragic event which has been recorded as a fisherman was pulling a caught ray onto his boat. Fortunately for the aquarist even the feistiest ray is not normally aggressive with its stinger, though rays can be very accurate with their aim, either slashing or stabbing with their powerful tails. In Amazonia most casualties happen when a ray is stepped on as it hides under the sand basking and snoozing during the day and so most stings are on the feet or lower leg. Rays would much prefer to move than be stepped on so locals know to shuffle their feet or poke the sand ahead of them with a stick when in the water, so that a ray can sense the motion and move out of the way without incident. For hobbyists it is the opposite, most people get hit on the hand or arm as they mess around in the aquarium while cleaning the tank or moving the ray. Sometimes it is a pure accident, others it is from carelessness handling the ray. Even on a dead ray the stinger is still toxic and very sharp.

Types of rays kept by hobbyists

The majority of rays kept by hobbyists these days , and the main focus here, are Potamotrygonidae, species of Elasmobranchs which are found exclusively in freshwater and includes more than 22 distinct varieties. At this time there is a lot to be learned about the relationship between these different varieties, whether they are sub-species or how closely they are related to each other. There is a dramatic and beautiful range of size , patterns and colors between them . Black rays with striking polka-dot patterns, such as the Leopoldi, Henlii and the less common small spot Itaituba Black rays are found in Brazilian Southern Amazonian clear water rivers. Two of the more dramatically patterned types are Tiger rays, named for their striking patterns and the markings on their tails, found in Peruvian Amazonia and the similarly patterned Flower rays, found in Northern Amazonia in some of the Colombia/Venezuela/Brazil border region rivers. There are many other local ray variants that are not as beautifully patterned but still are interesting. Castexi rays, one of the most polymorphic rays, with large array of distinctly different body patterns, are mostly found in the Western regions of Amazonia, with morphs such as Otorongo
(translated: Jaguar), Motello ( tortoise), Hawaiian, Tigrinus and others, all named for their beautiful patterns.

Pearl Rays

Itaituba Ray

Rare P 14 Variant

The debate on species differentiation

There is some debate concerning the different variants within species like Castexi and also the Black rays about how closely related to each other they may be. Whether they are truly separate species or are simply color morphs from slightly different habitats that would be expected to produce slightly different characteristics. Leopoldi, Henlii and Itaituba Black rays are prime examples often invoked in this debate, and their ability to easily interbreed throws more confusion on the whole subject. They are normally found in, and separated by, different Amazon tributaries. Leopoldi are found in the clear waters of the Xingu and Henlii are found in the waters of the Tocantins, clearly separate habitats according to the maps, but when the high water season is there it is impossible to know how different species are moved around by the massive inundation of floodwaters or if & how they migrate into different systems when water levels permit, only to become isolated again when the seasonal floods recede to lower levels. So it may be possible to find a species that may normally be only found in Peru or Colombia all the way down river in Brazil. It may also be that many of the species are in the middle of an evolutionary spurt, developing into new species. ‘Hybridization’ ( if they are actually separate sub-species) also seems to be a regular occurrence when natural circumstances permit and viable offspring suggests that Potamotrygon are not separate species.

Newly arrived young leopoldi - Brazil - Xingu

Flower Rays middle, leopoldi to right

Estrella and leopldi

Stingrays - a pest to some, a beauty to others

"In the Amazon all things are possible". During the low water season, when fish are concentrated in small areas and main river and Igarape channels, it is relatively safe to travel to remote areas to investigate ray population distributions; but this season is relatively short, often as little as 4 or 5 months only before the new rains start and the water levels rapidly and dramatically rise again. Much of Amazonia is still unexplored, and river courses change making it impossible to be absolute when it comes to discussing Amazonian fish populations and distributions. Some ray populations are booming to the point where they are considered a pest on the sandy beaches of the river. People are employed on popular river beaches in Brazil to keep the beaches clear of the rays, which tend to congregate in ‘dormitories’ to bask just under the sand in shallow water during the day, just the place where bathers walk . Basically those rays are killed as a pest and left to rot and feed the scavengers. There is a certain irony in this as those same rays could be sold alive to the aquarium trade instead and generate income. Some ray varieties are only found in limited areas and are not common, such as ‘Pearl’ rays. Rays are also an important local food fish . These are both contributing reasons for annual stingray quotas out of Brazil. However, these quotas often produce paradoxical facts. As a food fish many rays are worth much more alive to the aquarium trade than they are as food. One Henlii , Leopoldi, or Pearl ray, sold alive, is usually worth more on the aquarium market than a meat animal that might feed a whole village for a week or give milk for a few years. With a few exceptions, most ray species are plentiful in their native habitats and are considered pests, which contributes to an attitude that it is OK to smuggle rays out during the off-season or when all the quotas for aquarium export have already been filled. The laws of supply and demand fuel this market, with the final retail price for them adding incentive. Smuggled rays are often more expensive and usually less healthy than those that are exported through legal channels because of the extra ordeal those smuggled rays have to endure when exported this way. There are many tales of rays (and other smuggled flora and fauna) being hidden inside adapted gasoline cans or under floorboards aboard fishing boats. Luckily they don’t fit into people’s pockets.

Tiger Ray

Otorongo Ray

Tank size, tank mates, and feeding

One of the attractions for keeping rays in the aquarium is their behavior and intelligence. A healthy ray can learn very quickly how to recognize and hand feed from its owner. Hand feeding a large ray is a rewarding interactive experience for all those who do it. Of course, their ‘other-worldly’ appearance and their obvious beauty and character add to the pleasure. Most rays grow fast and if properly cared for will quickly grow to a size that is not suitable for a small tank . They require a large tank even at the beginning of their residency. Ideally they are kept as a single species, in other words they should be kept alone. Mixing other species can be precarious. One of the more popular tankmates are Arowanas, but if they are not matched for size with the rays then there can be problems. As a general rule of thumb when it comes to companion species ,"if a ray can fit it in its’ mouth then sooner or later it will eat it". If the Arowana is too big then it might attack the ray and will certainly beat the ray to food. On the other hand if the Arowana is not big enough then there is a good chance that eventually the ray will eat it. A friend of mine found this out the hard way when his 22" disc Tiger ray ate his 10" long $2000 red Asian Arowana. Plecos can present a similar problem, either they will be eaten by the ray or they will take free meals from the rays upper body slime coat, causing stress and possible secondary infections in the wounds and eventual death for the ray. Rays when healthy have voracious appetites and enjoy a range of foods. The easiest are live foods. California blackworms and earthworms are greedily sucked down. Ghost shrimp are a favorite food that often sends my smaller rays literally spinning with joy. Once used to it, most rays will also devour fresh frozen shrimp and other similar foods. Smelt , Salmon pieces, various shellfish and other kinds of seafood are often accepted, but some can be very messy and should be tested first or only fed just before a large water change. Rays can also be adapted to homemade recipes and prepared sinking commercial foods. Hand feeding your ray is one of the most rewarding experiences guaranteed to get a "WOW" from even the most jaded person. A ray is not inclined to sting, but can thrash about with happiness when being fed so when hand feeding it is important to be aware of where the rays tail is at all times and that the ray also be aware of you so that it won’t be startled. After a while rays can become very tame, allowing petting and actively investigating your hand for possible food.

Large China Ray

Water parameters

Amazonian rivers are all very soft water, with few minerals at all. Only the massive volumes of rainfall prevents the pH from falling sharply. Most of their habitat is around the pH 6.5 mark. When properly acclimated most rays can thrive in our tap water and do not require extensive chemistry to maintain them. However, they eat a lot and consequently excrete a lot so good husbandry is important in order to keep the water clean and the filters clear from sludge buildup. I recommend at least 2 water changes each week of at least 25%, using aged water. More if the tank is the least bit crowded. Rays are susceptible to organ damage from Ammonia and Nitrates poisoning so it is essential to monitor those levels and maintain them at constant zero through regular water changes and good biological filtration. Ammonia poisoning is one of the main causes of the ‘silent death’ as spoken of by Dr. Ross in his books. The damage is often done in original transit, which is often more than 36 hours in a box . A ray may take up to a couple of weeks to die from this, as it refuses food and either wastes away or dies from the internal toxins, and so it is sometimes hard to understand the linkage between shipping in bad water and the eventual death.

Acclimating your new rays, tank decoration

Some rays are more sensitive than others, the Paratrygon and China (small eyed) species are notoriously more difficult to keep than the Potamotrygons. Common popular species that are endemic to the Amazon are Histrix and Motoros and Reticulated. Many arrive under the catch-all name of ‘Teacup’ but this really only refers to their juvenile size and has no significance for knowing their species. These are often a first introduction to keeping rays as they are inexpensive compared to the more exotic rays. Some of those more exotic looking species, such as the Leopoldi, are very hardy and very active and aggressive in their behavior, others , like the Menchacai (Tiger) rays are thought of as being more shy, but this can be deceptive as most species are very active once they are properly acclimated and in a comfortable environment. Most people will never have to worry acclimating rays direct from import. If you are happy that the ray you are acquiring is healthy then acclimation to your tank or pool is not difficult. A few feet of airline tubing to siphon water slowly from the tank into the box/bag with your new ray are all that is needed. As the bag fills remove water until the ray is in tank water and all the original bag water has been diluted out. This takes from 30 minutes to an hour. The greater the differences in parameters between the tank water and the bag water the slower you should make the change. Once this is done remove as much of the water in the bag as possible and gently put the bag and ray into the tank and allow the ray to swim out of the bag into its new home. I keep my pools bare-bottomed but most hobbyists prefer a biotopical look and want substrate. It is important to avoid using anything sharp, such as sand that contains silicates, as this will tend to shred the rays underbody, allowing an infection to creep in, often leading to death of the ray. Estes is a brand name sand that is coated to make it smooth and is available in a variety of colors and is very suitable. The few times I have used a substrate I have chosen something to compliment my ray. For Black rays I use a black sand. Rays will tend to adjust their body color tone to blend in with their background, tending to get either noticeably lighter or darker over a period of a few days to a few weeks. Rays have relatively large brains and are one of the most intelligent of aquatic animals. A ‘dressed’ aquarium can help keep it amused, Driftwood and rocks to search around for food provides plenty of entertainment.

Breeding

Gender identification is simple. Just like their relatives Sharks and marine Rays, male freshwater stingrays have claspers, one on either side of the base of the tail and slightly underneath. In sexually mature males these are easily visible from above and with immature young they can be easily seen from their underside. Females do not have claspers. When mature enough to breed rays reproduce by internal fertilization and give birth to live young after a gestation period of approximately 3 months. ‘Pups’ are usually born in litters of from 2 to 8, depending upon the age and size of the rays involved. While still not a common event in the home aquarium several stingray enthusiasts and many large public aquariums around the world are now successfully breeding many varieties. As with all animals, breeding is a biological imperative for rays that only requires enough space and plenty of good food along with reasonable aquarium conditions and good husbandry to make your pets comfortable . This also makes the aquarium more enjoyable to watch and interact with for the already entranced aquarist.

Large male Motoro center, young leopoldi sides

(No photographs may be used without the author's written consent)