The goal of the present work was to study the efficacy of several lactic acid bacteria (LAB) as bio-silage inoculants of swordfish, ray and shark viscera by-products. A sterilised medium was initially used as a model system for assessing the potential of these microorganisms in batch and fed-batch cultures with re-neutralisation. In all cases, batch cultivations without re-neutralisation led to the highest production and yields of the main metabolites of LAB fermentation (lactic and acetic acids). The dynamics of these metabolites followed a conversion pattern from lactic to acetic acid with a final joint concentration over 16 g/L and final pH lower than 4.5. Both productions were modelled by means of logistic modified equations. In addition, the capability of LAB to ferment the fish visceral wastes was always high and easily reproducible. Finally, the results obtained for non-sterilised fermentations with Lactobacillus casei CECT 4043 were similar to those obtained for sterilised media, and a stable material was obtained after 72 h of culture.