In fishes, gills are the respiratory organs and they are projections of which of the following parts?
A. Nostril
B. Alimentary canal
C. Skin
D. None of the above

Hint: Fishes are characterized by the presence of gills.
Gills are essentially a type of respiratory organ which has evolved in fishes for carrying out respiration.
Gills contain perforated structures known as gill slits through which the water enters.

Complete answer: All the organisms belonging to superclass Pisces breathe through a specialized organ known as gills.
1. Gills are essential projections of the skin that is designed to absorb oxygen from the water.
2. Gills have a network of narrow blood vessels called capillaries.
3. Fishes take in water through the mouth and the water crosses the gills.
4. The blood flowing in the blood vessels present on the gills, pick up the dissolved oxygen in the flowing water, and in this way, the exchange of gases takes place that has many, many small blood vessels called capillaries.
5. As the fish opens its mouth, water runs over the gills, and blood in the capillaries picks up oxygen that's dissolved in the water.



So, the correct answer is option C. Skin.

Note: Gills are intricately branched organs located on each side of the head of fishes. Many aquatic animals such as some arthropods like prawns also possess gills, although fishes have advanced gills than arthropods.