Book excerpt: This publication is a practical manual that will guide the reader through the main principles of producing fish silage by fermentation and explain each step of the fermentation process needed to successfully become a fish silage producer. [Author] Fish, including shellfish, are highly nutritious and in much demand all over the world. [Author] However, fish processing by-products, in particular viscera (guts), are highly perishable. [Author] If not preserved or processed within a relatively short time after harvest, they may deteriorate rapidly making them unfit for human consumption or other uses. [Author] In many cases, processing leads to the removal of significant parts of the fish, such as the viscera, head, belly flaps and backbone. [Author] Depending on the species, these parts may represent between 30 percent and 70 percent of the fish. [Author] Some parts, such as gonads, belly flaps and backbones, may be used directly for human consumption, but most of the by-products of fish processing have traditionally been wasted, leading to negative environmental impacts, or they have been used in fresh form as feed for livestock or as fertilizers. [Author]