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.
Aquarium keeping (Rays requiring special cares): Rays such as the one
commonly known as "Antenna Ray" because of their extremely long, and
at the same extent, fragile, tail DO need special dedicated tanks, and should
be elected for a solo tank, unless looking for possible husbandry, allowing
them to move freely and gently. Same story, but for a completely a different
reason, is with rays such the "Otorongo Ray" reaching up to one meter
(3 feet) in disc size once fully grown up!
Keeping rays in the aquarium: handling VENOMOUS (Kind of risk: venomous
stinger) animals. Rays ARE venomous (either marine or f/w), or better yet,
the stinger hidden in their tail is venomous. Beyond the fact that the
f/w ray’s venom, like almost all animals living in water, is of protein origin,
there’s very little known (or at least on what ALL scientists agree!).
Fatalities are extremely rare, mostly occurring in the wild, (i.e.: kids
playing in shallow water and/or fishermen removing ray from their nets, and
mostly refer to injuries to abdomen or "big" veins), but even though
the risks are low You can’t avoid considering them. As far as science knows (or
BETTER, as far as I know), real risk comes from "residual of organic
matter" remaining in the wound (i.e. stinger’s parts, the stinger breaks
in pieces when the ray hits). Wound are – it’s said - EXTREMELY painful, and
require a very long time to heal. One of the books mentioned in bibliography
reports the wounded part was numb SIX YEARS after the
"shot"!!!
TIP: When setting up a tank, you’re highly
advised to use all technical stuff by working OUTSIDE the tank (such as
canister filters), and to avoid putting your hands in the tank as much as
possible .
BEWARE: Stingers are changed, by an healthy
animals, every few months and are said (if untreated) to retain their venomous
capacity for a LONG LONG period when buried and lost in the sand.
In the case of injuries (like
all organic venom's), first aid is dipping the wound in hot (as hot as you can
stand!) water and IMMEDIATELY after look for medical survey. This is a matter
to be seriously handled! A real "drug" against F/W venom does
NOT exist! Doctors will survey the situation to avoid infections and/or related
sign/symptoms/complications. CLEARLY tell your doctor what’s
happened and expect him to consider you … … … well, let’s say the truth: MAD!
These are not fishes for a
beginner or to play/kid with!!!
Husbandry and Breeding: These fishes are elasmobranches
("non-bony fishes") like sharks, marine rays, mantas and show an
EXTREMELY clear sexual dimorphism, in which the mature males carry two claspers
(along both sides of the tail). Reports of newborns are, mostly, related to
wild females caught when already pregnant. On the other hand, almost all the
captive births, as far as I know, refer to Potamotrygon motoro.
Pregnancy is internal and it’s reported to last three months, and the
youngsters are released (1 to 4) live and fully developed; equals in all way
but size to the parents. Most ray enthusiasts keep their rays (of different
species) in the same tank. I’m not aware of report of hybridization even
though, to me, and also according to more experienced ray keepers, it could
likely happen between rays of the same genus (but different species), like
those belonging to the Potamotrygon Genus (which, by the way, is the most
commonly kept). I happen to have a juvenile (likely male) Potamotrygon
leopoldi.
