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Freeloader Fish

Short answer: Juvenile trevally and some filefish shelter in or beneath jellyfish bells, using the stinging tentacles as a shield against predators and picking off food the jellyfish has caught or nibbling its tissue, the Reel says.

It describes the relationship as commensalism, in which the fish benefit and the jellyfish is largely unaffected. The footage, credited to elevatedmoments.co, shows small fish swimming inside a jellyfish.

VideoWrite-up1 sources
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What should you know about Freeloader Fish?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Juvenile trevally and filefish.

    DD-453-F01 · Write-up · Exhibit A (Fish)

  2. Inside the bell.

    DD-453-F02 · Write-up · Exhibit B (Shelter)

Video transcript: Freeloader Fish: Some Young Fish Hide Inside a Jellyfish's Bell

Did you know certain fish such as juvenile trevally and some species of filefish are known to swim within the bells of jellyfish for protection and sustenance. These fish use the jellyfish's stinging tentacles as a shield against predators as they are often immune to the jellyfish's venom. Inside the bell, they are also able to scavenge small prey items caught by the jellyfish or feed on the jellyfish's tissue without causing significant harm. This relationship is an example of commensalism, with a fish benefit from the jellyfish's defense mechanisms, while the jellyfish is neither significantly helped nor harmed. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 29.9s Reel ·

Video coming soonFreeloader Fish · Instagram Reel
Freeloader Fish: Some Young Fish Hide Inside a Jellyfish's Bell Instagram Reel · · 29.9s

The write-up

Some young fish hide inside a jellyfish's bell. The stinging tentacles keep predators away.

  1. Exhibit A

    Fish

    Juvenile trevally and filefish.

  2. Exhibit B

    Shelter

    Inside the bell.

  3. Exhibit C

    Defense

    Stinging tentacles.

  4. Exhibit D

    Food

    Scavenged prey.

  5. Exhibit E

    Relationship

    Commensalism, per the Reel.

Questions people ask about Freeloader Fish

Where do the fish hide?

Jellyfish.

Source: Write-up · Exhibit A (Fish) · Wikipedia: Commensalism

Which fish?

Young.

Source: Write-up · Exhibit B (Shelter) · Wikipedia: Commensalism

What protects them?

Shield.

Source: Write-up · Exhibit C (Defense) · Wikipedia: Commensalism

What do they eat?

Leftovers.

Source: Write-up · Exhibit D (Food) · Wikipedia: Commensalism

Relationship named?

One benefits.

Source: Write-up · Exhibit E (Relationship) · Wikipedia: Commensalism

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. Where do the fish hide?

    1. In the bell
    2. In sand
    3. In coral
    4. In kelp
    Show the answer

    Answer: A. In the bell Jellyfish. Source: Write-up · Exhibit A (Fish) · Wikipedia: Commensalism

  2. Which fish?

    1. Juvenile trevally
    2. Great white sharks
    3. Salmon
    4. Tuna
    Show the answer

    Answer: A. Juvenile trevally Young. Source: Write-up · Exhibit B (Shelter) · Wikipedia: Commensalism

  3. What protects them?

    1. Stinging tentacles
    2. Shells
    3. Speed
    4. Color
    Show the answer

    Answer: A. Stinging tentacles Shield. Source: Write-up · Exhibit C (Defense) · Wikipedia: Commensalism

  4. What do they eat?

    1. Scraps of prey
    2. Sand
    3. Plankton only
    4. Algae only
    Show the answer

    Answer: A. Scraps of prey Leftovers. Source: Write-up · Exhibit D (Food) · Wikipedia: Commensalism

  5. Relationship named?

    1. Commensalism
    2. Parasitism
    3. Predation
    4. Competition
    Show the answer

    Answer: A. Commensalism One benefits. Source: Write-up · Exhibit E (Relationship) · Wikipedia: Commensalism

Cite this case file

Easterling, Marcus. "Freeloader Fish." The Detail Department (DetailEnjoyer), case file DD-453, last updated Jan 10, 2025. https://detailenjoyer.com/case/freeloader-fish/

Permalink: https://detailenjoyer.com/case/freeloader-fish/ · Last updated

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