木曜日は、マリーのはてな日記/Marie the Scientist
Why Do Salmon Go Back to Rivers to Lay Eggs?」
Why Do Salmon Go Back to Rivers to Lay Eggs?
I saw a TV program about salmon.
Thousands of salmon were swimming up a river.
The program said salmon are born in the river moved to the sea and then go back to the river to lay eggs.
Why do they make such a big journey?
“Mom, why don’t they lay eggs in the ocean?”
“I have no idea.
I’m going shopping now.
Marie, do you want to come with me to the fish store?”
I like seafood and I like the man at the fish store.
I decided to ask him my question.
“Uokatsu-san, why do salmon go back to rivers to lay eggs?
Why don’t they lay eggs in the sea?”
First of all, you know what the eggs are called, right?
That’s salmon roe or ikura.”
“I know you like ikura very much.”
“Yes, I do.”
“Imagine ikura in the sea.
If you drop a big rock in the sea, it will sink to the bottom.
But ikura float in salt water.
Floating eggs are easy for other fish to find and eat.
Many fish like eating salmon eggs just like you.”
“That is why salmon don’t lay eggs in the sea, Marie.
It’s too dangerous.”
“Are the eggs safe in the rivers?”
In the rivers, salmon eggs sink down to the bottom.
A mother salmon digs a hole in the bottom of the river and lays eggs there.
Later, she covers them with small rocks to hide them.”
“Ah, that’s smart.”
Salmon lay a lot fewer eggs than other sea fish.
One salmon lays about 3,000 eggs.
On the other hand, many fish in the sea lay tens of thousands or hundreds of thousands of eggs.
That’s because it’s very hard for fish eggs in the sea to grow and become adult fish.
In the wild sea, eggs can easily get lost.
Also, there are many other living things in the sea that eat the eggs.”
“The sea sounds like a difficult place to live.
If the river is safe for salmon, why do they go out to the sea when they are young.”
“Well, to grow bigger.
There is more food in the sea like plankton.
Salmon stay in the sea for about three to five years to grow.”
Thank you so much, Uokatsu-san.”
“OK, Marie, what do you want for tonight?”
“I’d like salmon sashimi and ikura.”
I’ll get that for you.”
At dinner, I ate a lot of salmon and ikura.
It was delicious.”