Each item in Minecraft has a unique ID assigned to it, known as an item ID, this can be used in commands to spawn the item into the game. The item ID for bucket of salmon in Minecraft is shown below:
The Bucket of Salmon item can be spawned in Minecraft with the below command. Cheats must be enabled before this will work.
This item can be obtained by using any water bucket on a salmon mob (as of 1.13). You can then right click this item anywhere in the world to place the water in the bucket with the fish within - making it a useful item from transporting fish.