Serotonin is one of the monoamines that play an important role in food intake in mammalian species. The increase in serotonergic activity may reduce appetite. Fluoxetine as an active ingredient of Prozac is increased in serotonin content by blocking reuptake of it. Due to the release of these substances into the ecosystem, the role of fluoxetine on food intake and feed behavior of goldfish, Carassius auratus was investigated. In experiment 1, fish with 21-49 g weight divided in four groups of control: with no injection; saline injected; and two groups with 1 µg g-1 and 10 µg g-1 body weight fluoxetine. Animals were injected every other day for a total of 5 injections. Food intake calculated after each injection and fish reweighted at the end of the experiment to achieved weight changes. In experiment 2, 20 goldfish were selected in two groups of control and injected with 10 µg g-1 body weight fluoxetine to asses feed behavior test. Fish were injected every other day for a total of 5 injections and feed behavior was investigated after each injection. Food intake was significantly decreased after fluoxetine injections. In the Flu-10 group, low intake of food resulted in minimum weight gain among all treatments. Also, fluoxetine affected the feed behavior of goldfish and significantly was decreased in search and consumption of food. Results showed that this recently toxic environmental material can largely affect the food and weight parameters of goldfish