Abstract: In order to develop commercial technology for the comprehensive utilization of mackerel (Pneumatophorus japonicus) processing by-product, we carried out the non sterilized solid-state anaerobic fermentation of mackerel by-products to produce a novel protein source for feed with bioactivity. In addition, we monitored the content of histamine, acid-soluble protein and other indexes such as pH, total volatile basic nitrogen and antigenic protein; and investigated the evolution of microbial community during the fermentation by high-throughput sequencing technology, comparing the free amino acids and fatty acids before and after the fermentation. The results show that Lactobacillus plantarum HSCC-LP121 had the best comprehensive effect in increasing acid soluble protein content, reducing histamine accumulation and reducing volatile base nitrogen production. After 30 d of fermentation, the histamine content decreased to 0.629 g·kg⁻¹, which indicates that HSCC-LP121 had the ability to degrade histamine. Moreover, HSCC-LP121 inhibited the growth of potential histamine-producing microorganisms such as Psychrobacter and Pseudomonas. Besides, the strain could also inhibit the growth of potentially harmful fungi such as Aspergillus, and induce the growth of some aroma-producing yeasts.