Imagine yourself quietly paddling
along the Amazon river, taking in the scenery from your dugout canoe. You are
listening to the loud squawking of macaws, hearing the high pitched hum of
hundreds of species of insects, and eavesdropping on the conversations of the
nearest troop of howler monkeys. As you gaze into the quiet black waters, a
mysterious feeling comes over you as all of these ominous sounds seem to be
closing in from the invading vegetation on the banks. You try to discern the
moving figures in the dense undergrowth, when something catches your eye just
under the surface of the water. As you look more intensely you can see several
large, round disks, about three feet in diameter, gliding effortlessly through
the water. Upon closer inspection, they seem to look like stingrays. However,
stingrays are found only in saltwater, or so you thought, and you are a
thousand miles from the ocean!
In fact, there are stingrays found
in freshwater. Mostly in the Amazon, there are some species that inhabit the
tropical rivers of Africa and Asia. There are about twenty species all
together, belonging to three genera, and are perhaps the most feared by the
natives of all the freshwater fishes. This is a pretty serious reputation
considering the fact that the infamous piranha cohabitates with those species
which are found in the Amazon.
Stingrays are normally very
docile. As their name implies, however, they are equipped with a rather
formidable defense mechanism. Towards the end of their tail is a rather long,
serrated spine which is used solely for defensive purposes. Lengthwise on the
spine is a groove filled with venom-producing tissue. Attacks usually occur
while carelessly wading in shallow water where the fish often rests partially
submerged in the substrate. When stepped on, they lash their tail up and over
their back into the unsuspecting victim. If the animal survives the
envenomation, the ensuing secondary infection in the usually deep puncture
wound brings it closer to death.
Stingrays are well adapted to life
on the bottom. The muddy brown coloration with various mottled black patterns
effectively camouflages the animal in the river bottom. Their eyes are
slightly raised on the body so they can bury themselves almost completely in
the substrate and still view their surroundings for potential predators or
prey. They have two openings, one behind each eye, which take in water to pass
over the gills. This allows for the mouth to be positioned underneath the body
to search for any mollusks and crustaceans which also live on the river
bottom.
for any mollusks and crustaceans
which also live on the river bottom.
Both fresh and saltwater stingrays
are relatively primitive belonging to a group of fishes called elasmobranchs,
to which both sharks and skates also belong. Members of this group have some
interesting characteristics which separate them from other fishes. Whereas
most vertebrate skeletons are made of bone, elasmobranch skeletons are made of
cartilage, similar to the cartilage in our nose and ears. Some scientists are
particularly interested in the cartilage of certain elasmobranchs for its
cancer fighting properties. An external difference is the presence of five to
seven gill openings as opposed to just one in most fishes. Another adaptation,
which is employed most effectively by sharks, is the presence of an elaborate
system which helps to locate food below the substrate by detecting the
slightest vibrations that any potential prey might make.
As with other elasmobranchs,
freshwater stingrays give birth to relatively few young; clutch size averages
two to seven. They are ovoviviparous meaning that the young develop and hatch
within the mother and are born live. Fertilization is internal with the male
transferring sperm directly into the female via organs called claspers. Once
born, the completely developed, miniature stingrays are immediately ready to
fend for themselves.
Juvenile stingrays are notoriously
difficult to get to feed in captivity. They will readily refuse any and all
frozen foods that are offered initially. The best way to get them started is
to keep them in a smaller bare bottom tank and offer copious amounts of live
food, such as ghost shrimp, mysis shrimp, earthworms, and their all time
favorite, blackworms. It may take several weeks of intensive effort, but once
they start to feed, they will eventually convert to frozen foods such as
clams, smelt, shrimp, and any other meaty foods. After a while, they can even
be trained to take food out of your hands! Once they have converted to frozen
foods, they can be moved to a much larger display tank- and I do mean
larger. Although stingrays are relatively hardy (once they have been
acclimated) they have the capabilities to get very large-over two feet in
diameter- and live for over 20 years! These are the main reason why stingrays
are not suggested for your home aquarium.
If you are interested in
purchasing a stingray, be prepared to start them off in a large tank, over
four foot long by 18 inches wide (which they will soon outgrow and require
much more space over 8 foot by four foot wide)! Resist the temptation to
purchase the animal if your intentions of getting rid of it when it gets too
large. You will most likely find that you have a white elephant on your hands!
