The use of industrial fish processing waste as the only substrate to produce biogas may be an efficient procedure due to its characteristic lipid content. The relationship between the microbial community and the biogas/methane production was evaluated during the anaerobic digestion at 35 degrees C of two waste types derived from the fish processing industry. The experiments showed that fish waste (FW) and fish crude oil waste (FCOW) produced methane at 540.5 CH4 mL gVS(-1) and 426.3 CH4 mL gVS(-1), respectively. Clostridia, Synergistia were the predominant bacterial classes and the Methanomicrobia archeal class at the end of the anaerobic digestion in both substrates. The fungal community was similar in both treatments. The fungal diversity included orders of the Ascomycota phylum: Eurotiales, Sordariales, Saccharomycetales, Sporidiales, Capnodiales and Microascales. Representatives of Basidiomycota included Wallemiales and Tremellales. This research demonstrated that industrial fish processing waste can be efficiently converted to methane in a mono-digestion process. (C) 2019 Elsevier Ltd. All rights reserved.