Fish Gill Cross Section Under the Microscope
Fish Gill (Cross Section), Actinopterygii
This is a section through a fish gill stained with H&E. It shows how fish get oxygen from water using thin, feathery folds packed with blood vessels.
This cross section of a bony fish gill is stained with H&E. Two rows of long gill filaments branch off the gill arch, and each filament is held up by a rod of cartilage that stains purple. Thin plates called lamellae line the sides of the filaments, and they are packed with tiny blood vessels full of red blood cells. The lamellae are only a few cells thick, so oxygen can pass quickly from the water into the blood. Students can compare the thin walls here with the thin walls of the air sacs in lung tissue.
What to look for
- Gill arch: The thick supporting bar that the gill filaments attach to.
- Gill filaments: Long, finger-like projections extending from the arch in rows.
- Secondary lamellae: Tiny, thin plates lining both sides of each filament, like the teeth of a comb.
- Blood cells: Small oval red blood cells with nuclei, stained pink to red, inside the lamellae.
- Cartilage support: A pale rod running along the inside of each filament.
Questions and answers
What does a fish gill look like under a microscope?
A fish gill has a supporting arch with rows of long filaments. Each filament is lined with many thin plates called lamellae, which are packed with tiny blood vessels, giving the gill a feathery look.
How do gills get oxygen from water?
Water flows over the thin lamellae while blood flows through them in the opposite direction. This countercurrent flow keeps oxygen moving from the water into the blood along the whole length of the lamella.
Why are gill lamellae so thin?
Oxygen passes into the blood by diffusion, which works best over short distances. Thin lamellae put the blood very close to the water and give a huge surface area for gas exchange.
Compare it
- Category
- Vertebrates
- Scan magnification
- 20x
- Stain
- H&E
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