To start editing Aquaria (on mac) you'll need to click and select Show Package Contents. Then go to Contents→Resources→Data→Ingredients. This is where you edit what foods do what. Once the file is open, you should see a long string of words like this:
CrabMeat crab-meat Meat FishMeat fish-meat Meat FishOil fish-oil Oil JellyOil jelly-oil Oil RubberyMeat rubbery-meat Meat SmallBone small-bone Bone SmallEgg small-egg Egg SmallEye small-eye Part SmallTentacle small-tentacle Tentacle RedBerry red-berry Berry SmallEgg small-egg Egg HeartySoup hearty-soup Soup (+speed +defense) SeaLoaf sealoaf Loaf (~hp) SeaCake sea-cake Cake (+hp) PlantLeaf plant-leaf Leaf ButterySeaLoaf buttery-sealoaf Loaf (+hp) HealingPoultice healing-poultice Poultice (++hp) MagicSoup magic-soup Soup (+speed ++hp) etc.
The he more + signs, the more effective it is.
As an example, if you wanted to mod Sea Loaf, it would look like this:
SeaLoaf sealoaf Loaf (~hp). The ~hp means it heals you, but only a little. If you want to make it heal more, take the ~ out and add +s. The more +s you add, the more health you will receive.
+speedis adding speed for 45 seconds.
+energyis +# to energy shot for 45 seconds.
+tripis tripping out.
- The more + signs, the more time. "++" is around 30 seconds, and "~" is one second.
+webis web ability.
maxhpis maximum health, no + signs needed.
-blindmakes you see better.
+invincibleis self explanatory.
It is also possible to create or modify an existing recipe. For example you can copy the Hot Soup recipe and change the oil and meat entries to be SmallBone and SmallBone. From that point on, you can create Hot Soup by using Meat and Oil or a Small Bone and a Small Bone.