I think plasma packs made from fish fulfils slightly more thirst than those from frogs, but the difference is small and it will take quite a few packs to fill up the need each time. I personally find them inadequate and resort to use the voodoo doll method instead.
If you use the registered vampire lot trait, you will occasionally receive plasma packs. These packs gives more thirst than those made from fish or frogs.
Plasma fruits are really the worst. It just takes forever to fill the need with them, and it can't be improved by processing (e.g. juice fizzing).
About gardening, just start with basic plants and graft your way up to get more expensive plants (e.g. bird of paradise, orchid) as quickly as possible, but even the basic plants can get you through early on. You may also join the gardening career to make more.
As others have said, anything more than 50 simoleons is a good fertilizer. I usually find fishing too time-consuming and use rose as a reliable alternative.
