The Respiratory System of a Goldfish

Goldfish need to breathe oxygen in order to survive, but because they draw their oxygen from the water around them, the respiratory systems of fish are different from those of land animals. While land animals use lungs to separate oxygen from the air they breathe, fish like goldfish use their gills to get the oxygen their bodies need.

  1. Mouth

    • The respiratory system of a goldfish begins with its mouth. To breathe, goldfish draw in water through their mouth. Instead of swallowing this water, the goldfish closes its throat to direct the water to its gills. From the gills, the water flows out of the goldfish's body. Unlike mammals, which breathe in and out through our noses and mouths, goldfish don't exhale through their mouths.

    Operculum

    • At the same time that a goldfish opens its mouth to breathe, it closes its operculum, the bony structures covering its gills. The operculum are located on both sides of the goldfish's body, behind its eyes. Closing the operculum keeps the water in contact with the gills, allowing the goldfish to extract as much oxygen as possible. The operculum are also known as "gill covers," and unlike cartilaginous fish like sharks, only bony fish have them.

    Gill Rakes and Arches

    • The first parts of the gills that the water reaches are the gill rakers. The gill rakers act as filters, catching particles in the water. After all of the debris and waste particles have been caught by the gill rakers, the water passes through the gill arches. These are the structures that support the other parts of the gills. From the gill arches, the water moves on to the gill filaments.

    Gill Filaments and Lamellae

    • The gill filaments carry deoxygenated blood through the gills, and carry the rows of membranes where oxygen and waste products are exchanged between the blood and the water. These membranes are called "lamellae," and they absorb up to 85 percent of the oxygen in the water, while releasing carbon monoxide back into the water to be expelled through the open operculum. The blood flowing through the gill filaments and lamellae moves in the opposite direction as the flowing water, maximizing the absorption of oxygen into the bloodstream.