The Goldfish is an artifact that can be found in all three S.T.A.L.K.E.R. games.
"An artifact formed in the Vortex anomaly. Is activated by the heat of the body. Decide what's worse: radiation or knife wounds, and chose the lesser of the two evils. In any case you can sell the artifact for good profit." - Shadow of Chernobyl description.
"The result of a superinteraction of gravitational fields, Goldfish produces its own strong directed gravitational field and significantly increases stalkers' load carrying abilities, which explains why it's always in great demand. Emits radiation." - Clear Sky description.
"The result of an interaction between a large number of gravitational fields, Goldfish produces its own powerful internally directed gravitational field, which renders items within its range almost weightless. This artifact is most effective for reducing carried weight, which explains why it is always in great demand. Emits Radiation." - Call of Pripyat description.