How can u stop ur fish tycoon fish from dying without being on the game like every...

[♥Real Life Rosalie♥]

...second? I always pause it before I leave, but half my fish are still always dead when i come on the next day or even 6 hours later. I even bought the plant of nutrition, but my fish always starve anyway and it's always the same three 350 year old fish that survive. Please Help Me!