Examination of ionoregulatory characteristics of South American cichlids.

We examined ionoregulatory traits of four cichlid species from South America, oscars (Astronotus ocellatus), Tapajos cichlids (Geophagus sp.), Macmaster's dwarf cichlids (Apistogramma macmasteri), and keyhole cichlids (Cleithracara maronii), all inhabitants of ion-poor waters. K values for Na transport in fish held in 100 μmol L Na water ranged from 49 to 143 μmol L, and J values spanned 450 to 1205 nmol g h.