Depends on the species name - plenty of Knife fish out there are being labeled as "Tiger Knifefish". Gymnotus Coatesi and Gymnotus Carapo are two of the more common species that are mistaken for a Tiger. Pictures at all? Gymnotus Carapo I'd say no, just based on the aggression of mine, however with Gymnotus Coatesi I'd say go for it. A true Tiger, Gymnotus Tigre, at a small size I'd see it being okay, but not sure on the attitude as they grow larger. The Cory Cats will probably be left alone after one bad run-in with their spines, Blue and Gold Gourami are usually able to hold their own pretty well, and same with the Sharks. So it could work just fine, but that without knowing the for-sure species and the personality of the Knife.