If you are talking about fresh water Shad, they are very difficult. There can be no square corners in the tank at all. They will all huddle together in one spot, and suffocate on their own slime. They are very dirty fish, and very sensitive to water changes. When I used to fish a lot for Stripped Bass, we could only keep about a dozen in a round 50gal tank, with continuous fresh water being pumped through. Even then the maximum time we could keep them alive was 4-5 hours.