A total of 66 fish species belonging to 32 families were recorded between November 2012 and April 2014 in the southern arm of the delta to the Atrato River. Total length ( L T ; range: 1·7–48 cm) , total mass ( M T ), L T and M T relationships ( b values ranged from 1·8 to 3·7, mostly with negative allometric growth), and L T frequency (for 25 species) were estimated for freshwater, estuarine and marine species. L T and M T of Porichthys pauciradiatus and Membras argentea are given for the first time and maximum L T records for 14 species exceed those in the literature.