Astroblepus acostai is distinguished by the following characters: maxillary wattle goes beyond buccal disk; pelvic fin does reach beyond the anus; pre-dorsal distance goes beyond the origin of the adipose spine; pectoral fin with a single radius and 11 more of them branched; pre-maxillary with two and a half rows of teeth, the outermost having 7-8 conic curved teeth; inferior lobule of the caudal fin is bigger that the superior lobule; 22 free vertebrae, the fifth ceratobrachial bone with 8 teeth in the anterior region (Ref. 93750).