Importance of Carbon Dioxide to Fish

Fish habitats, from ocean environments to small ponds, need adequate dissolved gases

in the water for respiration, or breathing. Low levels of dissolved gases within water reduce fish populations or force the fish to move to a different area for respiration. Carbon dioxide is one of the dissolved gases that is an important factor in fish respiration health.

  1. Fish Breathing Basics

    • Fish use thin membranes, called gills, that allow absorption of dissolved gases. In particular, fish absorb oxygen from the surrounding water. The oxygen dissolves across the gill membrane and into vascular capillaries. The blood within the capillaries circulates the oxygen throughout the fishes' body. Carbon dioxide is a byproduct of the respiration process, going back out into the water.

    Plant Contributions

    • Carbon dioxide is important to fish since it is used as a necessary gas exchange with plant life. During the daytime, plants in the water, such as kelp, produce sugars for energy through photosynthesis. The plants use the dissolved carbon dioxide, provided by the fish, as fuel for photosynthesis. The plants emit oxygen into the water as a byproduct of photosynthesis. During the night, photosynthesis temporarily stops, while fish consume the oxygen provided from the plants, effectively sustaining life.

    Significance

    • The exchange of oxygen and carbon dioxide between plants and fish is imperative for sustaining both organisms. During a 24-hour cycle, the amounts of oxygen and carbon dioxide vary greatly. Oxygen has the most concentration within the water at sunset. The plants have photosynthesized all day, producing copious amounts of oxygen molecule byproducts. In contrast, carbon dioxide is at its lowest concentration at dusk, since the plants have consumed the molecule all day long for photosynthesis.

    Excessive Levels

    • Fish cannot tolerate large concentrations of carbon dioxide. Fish need the plants to control the carbon dioxide levels in a water body. Carbon dioxide concentrations below 10 parts per million (ppm) are considered a healthy fish water environment. However, concentrations of 20 ppm or higher interfere with fish respiration. Oxygen within the fishes' body cannot adhere to the blood cells correctly if the fish has a high carbon dioxide concentration within its body. The fish will suffocate from excess carbon dioxide levels.