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Fish Gills, Respiration and Ventilation Help

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By — McGraw-Hill Professional
Updated on Aug 30, 2011

Introduction to Fish Gills, Respiration and Ventilation

Land-dwelling animals – mammals, birds, reptiles, and amphibians – use air as a means for both respiration and ventilation. And associated with this characteristic, they have developed lungs, which inflate and deflate with air.

Aqueous (water-dwelling) animals, such as fish, however, ventilate water through their mouths (Figure 18.2). The water passes through the pharynx (throat), and then out across a set of curved gill arches. The gill arches consist of a series of thin, thread-like gill filaments. Thin plates on the surfaces of the gill filaments serve as the actual points of respiration (gas exchange). Water passes through the narrow gaps between the plates and moves in a single direction, out towards the edge of the operculum (oh- PER -kyuh-lum) or gill “cover.”

The Respiratory System: Breath of Life Fish Gills: Respiration and Ventilation through the Water

Fig. 18.2 Fish gills: Extracting oxygen from the water.

As the water passes, O 2 molecules diffuse out of the water, and into tiny blood capillaries. Simultaneously, CO 2 molecules diffuse out of the fish’s bloodstream, and into the water. This mechanism for gas exchange is very effective. A limiting problem, however, is that the gill arches are very soft and tend to easily collapse. There is also no defense mechanism to protect gill arches in fish from dehydration.

Study suggestion: Ask yourself the following question: “So, why can’t most fish just use their gills and extract O 2 from the air? Why can’t most fish breathe outside of the water?” Use the preceding hints in your reading to help you.

Practice problems for these concepts can be found at:  The Respiratory System Test

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