FRESHWATER STINGRAYS
A Few words on origin, evolution, and original biotopes: Freshwater stingrays, as odd as it may seem, are much closer – from an evolutional point of view - to Pacific rays than to their counterparts living in the Atlantic. Ages ago they got trapped while browsing for food in an estuarine area in what is the actual Amazon basin when the Andes rose (because of a terrific earthquake). Before that time, the Amazon river was flowing, as a matter of fact, into the Pacific ocean. As a consequence of that traumatic (at least from a geological point of view) event, the salt rate begun to lower, and step by step, the Amazon rays became used to fresh water. At the present time, other rays from Africa and the Far East can be considered, from a biological point of view, the link between Amazonian FW stingrays and the ones living in salt environments. About 90% of FW stingrays presently available for the hobbyist’s market are from the Amazon Basin.
Aquarium keeping (aquascaping, specific needs, tank mates). Rays to be kept in aquarium should be chosen from already quarantined (and YET feeding) specimens. Dealing with newly arrived wild collected specimens may result in being a tricky matter. Never forget that rays are scaleless fishes, and treating them properly is neither easy nor "simple". Under given circumstances, rays have to get an antibiotic (or other drug) by injection (simply think about drug’s quantity to inject!). The second point to consider when it comes to dealing with rays is THINK BIG, as big as you can … and then go a step further! Some specimens such as "Otorongo Ray" are reported to attain up to one meter in disc size. Growth rate is related to food supply, to a certain degree, but correctly kept rays are said to be fierce feeders and fast growers! When dealing with small/medium sized rays aquascaping in the tank could be in the "Amazon River" fashion but, then, when it comes to dealing with adult (and possibly large) specimens, their size and strength has to be, as a matter of fact, taken into due consideration! Tank mates have to be, then, chosen (beyond other rays) among Amazon heavyweights such as Oscar (Astronotus ocellatus), Arowana, and more; even if there are reports of rays happily going on with Discus and Angels (P. scalare/P. altum) and even "big sized" characins in their quarters! Housing sucker mouth catfishes with rays can be a risky matter, despite the fact they come from the same biotope, since most of the former fishes (catfish) have, or could have, the bad habit of "sucking" the slime coat from the ray and this habit could result, in the end, in bleeding wounds likely to end as infection "start-center". BTW, most feared are said to be "common plecos" (hypostomus sp.). I’m aware of a good compatibility between rays of different kinds, even with a fair difference in size, and aggressiveness is almost always at low levels! One of the habits shown by rays to declare their own higher lever in tank’s hierarchy (against other conspecifics) is known as " topping": the dominant specimens simply tops (swim over him and the rest) another one: A bit far from cichlid’s habits, isn’t it?
Aquarium keeping (Technical supply, water chemistry, feeding). When dealing with those fishes filters (always use more than one unit: better safe than sorry!), they are always, no matter how hard you try, undersized. When aquascaping the tank, special care should to be put in place to avoid contact between rays and heater(s) unit especially if of high power (in terms of applied watts): FW ray get burnt EASILY! And their recovery is said to be anything but easy! These wonderful creatures are extremely sensitive to high (well below cichlids average, FYI!) levels of nitrite/nitrates. Warning: when readings go beyond certain limits over extended periods – no sure level is reported – this may result in a sort of irreversible poisoning ending with the death of the animal. Hence, frequent water changes are a must, with suggestions ranging from 20% every two weeks up to 30/50% (and more!) weekly, depending on the ray(s) size, tank size, and filters in use. Water chemistry should be kept on the acidic/neutral side, with water temperature neither below 22° C, nor exceeding 30° C. Whenever something goes wrong with water chemistry, FW rays show their dislike by stopping to get food and/or showing a lethargic behaviour. Feed them with HEALTHY feeder fishes (this could trigger them to start chasing smaller tank mates; be conservative!), fish’s fillets, shrimps/prawn, earthworms, mealworms, and alike. They should refuse, as a rule, "canned" food.