Grass carp are perishable due to the growth of microorganisms during storage, which restricts the development of its processing industry to some extent. Microbial interactions are important factors affecting food spoilage. In order to explore the roles of microbial interactions in the deterioration of grass carp quality, Pseudomonas putida (P. putida) and Shewanella putrefaciens (S. putrefaciens) were co-inoculated into grass carp flesh and arginine solutions. The effects of the interactions between P. putida and S. putrefaciens on their growth and spoilage potentials were evaluated by detecting total viable counts, soluble peptides, free ammonia, and putrescine changes in co-inoculated fish flesh and the putrescine production in the co-inoculated arginine solutions. Results showed that P. putida had potent activity in producing siderophores and inhibited the growth of S. putrefaciens in fish flesh by competing for ferric irons. The interactions between P. putida and S. putrefaciens increased the ammonia content of fish flesh in the first 11d of storage and facilitated the putrescine production in the first 8d of storage, but had no promoting effect on the production of soluble peptides. After 11d of storage, P. putida and S. putrefaciens did not promote the production of free ammonia and putrescine through interaction effects due to the inhibition of S. putrefaciens growth. P. putida was able to enhance the putrescine-producing activity of S. putrefaciens by providing arginine-degrading products through the arginine deiminase pathway. Overall, P. putida and S. putrefaciens facilitated the quality deterioration of grass carp during storage (0-11d) through microbial interactions like metabiosis. S. putrefaciens played a primary role in grass carp spoilage and the interactions with P. putida. More attention should be paid to the control research of S. putrefaciens in the development of fish preservation techniques.