Finding Nemo’s Clownfish

Predict

In Finding Nemo, Nemo’s mom is lost at the start of the movie, and his dad, Marlin, raises him alone. In a wild clownfish family, could a dad like Marlin become the mom?

Circle one. Yes / No

Why?

Watch

1. Finding Nemo got the clownfish wrongyoutube.com/shorts/62srRdYYCAg
2. Nemo is probably not Marlin’s sonyoutube.com/shorts/5GJUhGE19qA

Word of the day

Larva (LAHR-vuh). A young animal that hatches from an egg and looks unlike the adult it will become.

• A tadpole is the larva of a frog or toad. Video 2 uses the plural, larvae.
• In ancient Rome, larvae were harmful ghosts.

Bonus words. Protandry (pro-TAN-dree) means male first, from prot-, “first,” and andr-, “male.” Philopatry (fih-LOP-uh-tree), the word in the title of the 2016 Kimbe Island paper by Salles and others, means an animal stays near, or comes back to, the place where it was born. It joins Greek phílos, “loving,” and Latin patria, “homeland.”

Questions

1. In a study of wild Red Sea clownfish, breeding males carried testis tissue and immature ovary tissue at the same time. After scientists removed the breeding female, the male’s gonad began to change about 24 days later, and the male tissue was gone by day 50. How does a breeding male clownfish become the new breeding female? And what happens to the largest non-breeder and to each smaller clownfish in line?

   Hint. The breeding male already carries two kinds of gonad tissue. Which kind matures, and which kind disappears?

2. Clownfish parents tend their eggs for about a week before hatching. Their care rises as the embryos develop and peaks on hatching night with fanning, mouthing and biting at the anemone, and then the larvae drift away. How could egg care raise the number of offspring that clownfish parents produce? What experiment would test your explanation?

   Hint. Compare eggs that get care with eggs that get none. What would you count?

3. On Kimbe Island, 56% of the young fish that settled had hatched from Kimbe Island parents, and the other 44% arrived as larvae from other reefs. Yet relatives shared an anemone only about 2% of the time. What path does a clownfish larva take from hatching night to settling? And how does that path let most Kimbe Island settlers have Kimbe Island parents while relatives rarely share one of the island’s 310 anemones?

   Hint. A larva drifts for about 10 days before it settles. When a larva settles back on Kimbe Island, how many anemones does the island offer?

4. The Kimbe team never followed a larva across open water. Divers clipped a tiny piece of fin from each fish, and the team read 22 DNA markers from each clip over six rounds of sampling between 2003 and 2013. How can DNA markers link a young fish to one breeding pair? And why would the Kimbe team sample six times instead of once?

   Hint. At each marker, a young fish carries one number from each parent. Which fish are alive during any one round of sampling?

Claim, evidence, reasoning

Going further: anemone math

1. Kimbe Island has 310 anemones. Each anemone holds one breeding pair and up to four non-breeders. What’s the most clownfish Kimbe Island could hold at one time?

   Circle one. 620 / 1,240 / 1,860 / 2,927

   Hint. Find the most fish one anemone can hold first. Then multiply by the number of anemones.

2. Kimbe Island’s 310 anemones hold a limited number of clownfish at one time. Over ten years, the scientists identified 2,927 different fish. Why could the Kimbe Island scientists identify more clownfish over ten years than Kimbe Island holds at one time?

   Hint. Think about how the fish in one anemone change over ten years.

3. Each Kimbe Island anemone holds one breeding pair, and the island has 310 anemones. What limits how many clownfish can breed on Kimbe Island at once?

   Hint. Think about what a non-breeder has to wait for before it can breed.

Exit ticket