Its common practice to prune tomato plant for it to do well. In the process there are lots of suckers and leaves cutting around.
I accidentally left behind one leave and its take root. This is one way to propagate tomato plants, those cutting you could put it in a glass of water, after few days it will take root.
In Aquaponics due to growbed is actually equivalent to that glass of water, these plant cutting easily take root.
So if you see a good tomato plant, ask the owner for that cutting or suckers that he's throwing away and do the necessary to make it root.