Blind Cavefish: a two-minute wildlife lesson

Weird and Wonderful · day 7 of 7

Five facts

1. Blind Mexican tetras store four times more fat than their sighted cousins, which helps them survive scarce meals in dark caves.
2. Cavefish from the Pachón caves have no eyes at all, but a super-sensitive lateral line picks up tiny changes in water pressure.
3. There are about 30 distinct cave populations in three karst regions of northeastern Mexico.
4. The skin over the eye sockets thickens into a protective flap as the fish matures, whatever the lighting.
5. Even without working eyes, cavefish still react weakly to light, and young larvae respond to shadows using the pineal eye.

The quiz

1. How much more fat do blind tetras store than sighted ones?

• Half as much
• The same amount
• Twenty times more
• Four times more (correct)

They store four times more fat than their sighted cousins.

2. What helps eyeless tetras sense their surroundings?

• A hyper-sensitive lateral line (correct)
• Long whiskers on the tail
• Clicking sounds
• A glowing nose

A hyper-sensitive lateral line detects tiny water pressure changes.

3. About how many distinct cave populations are there?

• About 3
• About 300
• About 30 (correct)
• About 3,000

There are about 30 distinct cave populations.

4. What does the skin over the eye sockets turn into?

• A transparent window
• A protective flap (correct)
• A bright patch
• A hard shell

The skin thickens into a protective flap as the fish matures.

5. Which organ still detects shadows in early larvae?

• The tongue
• The swim bladder
• The pineal eye (correct)
• The gills

Young larvae react to shadows using the pineal eye.

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