How Goldfish breathe through Gills

A goldfish does need to breath oxygen but instead of using lungs like mammals, they use a pair of gills. Goldfish gills work much like a pair of lungs but instead use the dissolved oxygen in their water. Since a goldfish lives its entire live in water, it uses osmosis These gills are located right behind the the head and eyes on both sides of the goldfish’s body and covered by the operculum, commonly called gill covers.




The process of breathing for a goldfish starts when it draws in oxygenated water through its open mouth and closes it’s throat and operculum. The goldfish then shuts it’s mouth and opens its operculum forcing oxygenated water out through the gills. Before the oxygen in the water can enter the goldfish’s blood stream, it must pass over important parts of the gills.




The oxygenated water will first get filtered when it hits the gill rakers. The gill rakers catch free floating food particles and other waste materials. They act much like the hairs inside your nose do to filter out dust and debris. After the gill rakers, the water passes through the gill arches and then over the gill filaments. The gill filaments contain two rows of a series of thin membranes called lamellae. The filaments that contain the disc-like lamellae are set up to create a large surface area in a small space. This allows for a maximum amount of gasses to be exchanged; up to 85% of all the oxygen in the water is taken in when it passes over the gills. Oxygenated water that passes over the lamellae permeate into the goldfish’s blood stream through the tiny capillaries in the lamellae. This is a similar process that occurs in lungs of mammals when oxygen gets absorbed through the capillaries in the alveoli that are set up to have a large surface area in a small space. At these capillaries, clean oxygen enters the goldfish’s blood stream while the byproduct, (deoxygenated) carbon dioxide exits and is forced out into the water through the gill covers.




Note: Colder water contains more oxygenated water than warm water. By keeping a goldfish’s tank water cooler than 70*F, oxygen levels will be elevated, making it easier for goldfish to breath.