Red leaf lettuce is the easiest type of lettuce for goldfish to digest. If the lettuce is purchased at a grocery store, wash it thoroughly with vegetable rinsing solution to remove pesticides use by commercial growers. Red leaf lettuce grown in your own garden or purchased in the organic section of a farmers market or grocery store are the safest options for your goldfish. Give the red leaf lettuce a final rinse in warm water to soften and attach it to the interior wall of the aquarium with a food clip and watch him devour his nutritious treat.
Fresh baby peas are a favorite treat of goldfish. Boil the peas until they are soft, cool and store them in the refrigerator. When it’s time to feed your goldfish, take a pea between your fingers and gently squeeze off the outer skin. Mash the soft part of the pea between your fingers and drop it into the aquarium. Feed one pea at a time until your goldfish learns about the treat. Too many peas in the tank will cloud the water and dirty the aquarium gravel.
Just like all other fresh goldfish treats, all fruits need to be washed thoroughly before placing them in the aquarium. Drop a whole raspberry or blackberry into the goldfish tank and allow him to pull off individual pieces of the berry. Apple can be softened by boiling, and small pieces of skin-less fruit may be offered. Also try seedless grapes, with the skin removed.
Scour your local pet store for live plants to add to your aquarium. Since goldfish seem to always be hungry, be forewarned they may nibble the following plants to a nub in no time. Be prepared to refresh your plants as needed, depending on the amount of goldfish present in the aquarium. Safe live plants for goldfish include java moss, java fern, anubias and elodea.
First Tank Guide: Goldfish Care Basics
PetPlace.com: Healthy Food for Your Goldfish
Aquatic Community: Fancy Goldfish
Happy Goldfish.com: Diet and Nutrition