Life Fruit: Grown from "Special Seeds". You have to plant them before you know what plant it'll grow (Money Tree, Flame fruit, Life Plant)
Death Fish: Go to the graveyard (or to the shore with the no fishing sign in riverview) at night and wait for the small group of fish to become 'foggy' or 'smokey' (between 10pm and midnight). At this time you have a chance to fish up Death Fish.
Both require a high skill in gardening/fishing to obtain.
You will have to grow the lifefruit (so your sim must have high gardening skills). Seeds that can be found around town with either be common, uncommon, rare, or special. Some say the special ones are mostly found around the science center and the cemetery. Finding one does mean that it will be a life fruit one for sure; only way to know is to grow it to maturity. More on gardening can be found here:
Comments
Death Fish: Go to the graveyard (or to the shore with the no fishing sign in riverview) at night and wait for the small group of fish to become 'foggy' or 'smokey' (between 10pm and midnight). At this time you have a chance to fish up Death Fish.
Both require a high skill in gardening/fishing to obtain.
http://sims.wikia.com/wiki/Gardening_(The_Sims_3)
The Deathfish is something that you will need to have level 10 fishing to get, and you can only fish it up in the graveyard between midnight and 4am.