Lewis & Short

ex-dorsŭo or -dorso, āre, v. a. [dorsum; lit., to deprive of the back; hence, in partic.], of fishes, to take out the backbone, to bone (ante- and post-class.): congrum, muraenam exdorsua, quantum potes, Plaut. Aul. 2, 9, 2: pisces (with desquamare), App. Mag. p. 301, 3; cf.: exdorsuare, dorso nudare, Non. 17, 29: exdorsua dorsum confringe; alii, exime, Paul. ex Fest. p. 79, 12 Müll.