12-01-2009, 10:31 AM
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I got carried away with the cihclids and missed the Columbian shark question in the first post; sorry about that.
These are not at all compatible, due primarily to water parameter differences big time. Dwarf cichlids need soft, acidic water. Columbian sharks should have hard, basic (alkaline) water. And being a predator, the shark would eat the cichlids once they can fit into its mouth.
This fish appears to have some identification issues; in researching it (never having kept it myself) I have come across three different genera, Sciades seemanni, Arius seemanni and Hexanematichthys seemanni. The fish appear the same from the photos. General concensus is that juveniles should have brackish water or at least hard alkaline water, adults require marine setups (full salt). Given this information, I would suspect maintaining this fish in pure freshwater, particularly soft and acidic, might cause internal issues very quickly and lead to future health problems. This is common when fish are kept in what I'll call unsuitable conditions, whether from water parameters and/or tank size, as juveniles. Fish grow constantly throughout their lives, so unsuitable conditions right from the start can have long-term effects. I would find another home for this fish unless you can provide a brackish/marine environment in a minimum 4-foot tank now; it will quickly outgrow such a setup of course, so plan ahead.