Isn't it true that you must have perfect bait for the whole foodchain from the cheese untill the deathfish?
I mean first grow perfect cheese (by using lifefruit, perfect lifefruit), than catch with that cheese the perfect alley catfish, with the catfish you catch the perfect angelfish and than finally you should have no trouble with catching perfect deathfish, right?
I never tried it before, but I asume that when the whole foodchain is perfect, it should be more than normal that the deathfish would be perfect to. Maybe the game remembers all the steps.