I T was a lovely day in May. The sun was shining, the grass was green, and the bushes on the banks of the river Thames were covered with fresh leaves.
In a hollow place in the river a little fish was building a nest. The fish was a stickleback. It was not more than two inches long. It had three spines sticking up on its back. Boys often catch this fish, and keep it in bottles or sell it to people who have aquariums.
It was more pleasant to watch him at work under the shade of the bushes. He brought little pieces of fine root-threads and narrow grass, and made them into a tiny saucer at the bottom of the river. Then he brought more pieces and stuck them on with slime from his mouth. In this way he made sides and a round roof. When he had done, the nest was as big as a large gooseberry.
It was about six inches below the top of the water, and had a hole right through it. When the stickleback put his head out at one end, his tail stuck out at the other. But he had not built it to live in. He wanted it for the eggs of his young ones.
He was a lovely little fish with a shining back, and bright red belly. He had a bluish green eye that shone like a jewel.
Now that his nest was built he swam off to fetch a mate. He soon came back with another fish, not so bright as himself. He played with her, and drove her, and coaxed her, till at last she went in at one hole of the nest and, after a little while, came out at the other end.
She had deposited a tiny packet of yellow eggs, which she left behind her. Then she went away and took no more care of them.
The father stickleback now went through the nest and took charge of the eggs. Each egg was not bigger than a poppy seed, and the whole bunch was very tiny. He shook the nest up and poked the eggs into a snug, safe corner. Then he swam over the top of the nest, waving his fins, so that fresh water went in and out.
Sometimes he went into the nest and brought out some dirty sand in his mouth. This he puffed away into the water. You see he wanted to keep the nest clean.
He did this every day for three weeks, till the eggs were hatched. Then a number of tiny fish came out. They were so small and transparent that you would think no other fish would see them. But the stickleback knew better. There were plenty of hungry fish watching to eat the tiny fry, which were very weak and had to carry a bag of food under their body, to suck in till they could eat.
So the brave little stickleback stuck up his three spines, and dashed angrily at any fish which snapped at his little ones. He seized their fins, and struck at their eyes and drove them away.
He made a small round place in the sand at the bottom of the river and gathered the little sticklebacks into it, and there he watched over them. Even after their spines were grown and they could swim boldly, he followed them out into the river to see that they were safe.
You may find plenty of stickleback's nests in rivers and ponds, if you look carefully for them. Or if you catch several sticklebacks in a bottle and put them in a large pan with plenty of weeds and food, most likely you will see a stickleback build his nest, and learn what a good father he is.