2 literature references:

Author: Heckman, C.W.
Year: 1991
Title: Alosa pontica kessleri (Grimm 1887).
Source: p. 325-336. In H. Hoestlandt (ed.) The freshwater fishes of Europe. Vol. 2. Clupeidae, Anguillidae. AULA-Verlag Wiesbaden.
Author: Berg, L.S.
Year: 1962
Title: Freshwater fishes of the U.S.S.R. and adjacent countries. volume 1, 4th edition.
Source: Israel Program for Scientific Translations Ltd, Jerusalem. (Russian version published 1948).