The Black-Fin Shark is one of the few Catfish at home in the brackishwater tank
by Neale Monks
Columbian shark catfishes are among the most desirable of all aquarium fishes. They are big, powerful looking
animals with sleek silver bodies and active natures. Although distinctly predatory, they are not aggressive and
on the contrary, can be bullied by fishes like cichlids. Arius seemanni (sometimes incorrectly referred to as
A.jordani) lives in fresh and brackish waters, and sometimes enters the sea. In aquaria hard, alkaline
water is critical, as is a powerful filter and good oxygenation. A specific gravity of 1.005 to 1.015 is about
right, with regular fluctuations within this range being beneficial to health. They need a big, roomy tank with a
powerful motorised filter.
Some Arius have been bred in captivity, but not this species. This is presumably because of some missing
trigger, but what that is is not known. Females are noticeably stockier and
develop swollen pelvic fins when mature. Many Arius mate in summertime at sea, and being a mouthbrooder
the male carries the few large eggs until they hatch, depositing the young fish in rivers.
Arius appreciate a dark aquarium with a definite current. Decorate the tank with a thin layer of sand or gravel
for burrowing in, with large rounded boulders to make caves and lairs. Keep in schools of three or more.
Small specimens are adaptable, but above 12 cms (4 inches) they become distinctly restless, perhaps feeling
some migratory drive. Fluctuations in salinity and strong water turnover are essential at this stage to settle the
fishes down. Compared with other catfishes, these fish are not nocturnal and swim constantly, often into a part
of the tank with a steady flow.
Shark catfishes are so named because of their powerful, sleek shape. They swim gracefully, something not
easily appreciated in a small tank. Arius seemani has venom glands in the base of the dorsal fins, and should
therefore be handled with care. Arius seemani also possess glands in the mouth capable of secreting
anticoagulants, which they use when hunting. More obvious to the aquarist are the continual drumming noises
they make. These are possibly used for echolocation and for communication between fishes in the school.
A local name for Arius fishes in South America is crucifix fish. When cleaned and suitably painted, the skull of
this fish is sold as curio. On the underside a crucifixion scene can be imagined, and on the dorsal surface a
bishop raising his arms in a blessing.
The name of the genus, Arius, signifies that the fish is 'of the war-god Ares' not altogether unfitting considering
their impressive adaptations to the predatory lifestyle! All in all these are fascinating fishes.
Black-Fin Shark; Shark Catfish; Colombian Shark