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Sea Catfishes, family Ariidae
Sea catfishes make excellent aquarium residents, being hardy, peaceful, and easy to feed. Although predatory, they are gregarious and best kept in groups of at least three specimens. They mix well with other large, peaceful fish including scats, monos and archerfish.
Sea catfishes are powerful, sleek fish that swim strongly and as they cruise into estuaries and across shallow seas searching for their favoured prey, small fish and crustaceans. To help them find food they use their whiskers and electrical sense just like other catfish, but they also produce sounds apparently used for echolocation. More obvious to the aquarist are the continual drumming noises they make. These are probably used for some sort of communication. Sea catfishes possess glands in the mouth capable of secreting anticoagulants, which they use when hunting to weaken their prey. They are also well defended, with sturdy spines in the pectoral and dorsal fins armed with a powerful venom. Needless to say these fish should be handled with care.
In South America sea catfish are sometimes called ‘crucifix fish’. When cleaned and suitably painted, the skulls of these fish are sold as curios. 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 one genus of sea catfish, 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.
The Colombian shark catfish Sciades seemanni is by far the most widely traded sea catfish. They do well in large tanks with ample swimming room and a strong water current. Salinity isn’t critical, but aim for around SG 1.005 for juveniles and SG 1.010 for adults. This species can also be kept in a marine aquarium. Maximum size in aquaria is around 15-20 cm (6-8 inches) though in the wild this species can be twice that size. This species is very gregarious and easily bullied, so choose tankmates with care. Older books refer to this species as Arius seemanni, Arius jordani, and Hexanematichthys seemanni.
Some species of the closely related genus Arius have been bred in captivity, but not the Colombian shark. This is presumably because of some missing trigger, but what that might be is not known. The small size of the Colombian shark should mean that captive breeding is possible. In captivity at least, this species reaches about 30 cm (12 inches) in length, but the females are noticeably stockier than the males and develop swollen pelvic fins when mature. Many ariid catfish mate in summertime at sea, the male brooding a few large eggs in his mouth until they hatch, when he deposits the young fish in rivers and offers them no further protection.
Occasionally other sea catfish appear in the trade, such as Hexanematichthys sagor. Apart from differences in size and potentially water chemistry requirements (some species are strictly freshwater fish) basic care is consistent and similar to that required by Sciades seemanni.