THE FISH OF OUR ROCK-POOLS
The pools left by the falling tide have many an interesting thing to show us. There are living creatures in plenty, besides the pretty weeds, shells, and other objects. Shrimps, Prawns and Crabs abound in the rock-pools and shallows, with anemones and shellfish of all kinds. In the rock-pools we shall also find the interesting little fish whose story we glance at in this lesson. Of course there are baby flat-fish, and large fish too, along the shore. But these are only visitors. The real rock-pool fish are those which live their lives there.
Some of them are tiny things, two or three inches long. With quick movements like Shrimps they dart away as you approach. They have a way of hiding under weeds and rocks, being very clever at "hide-and-seek," and knowing all the dodges. But, by using a net, you will soon capture a few of them. Then you can put them in a small pool and examine them; or even keep them in an aquarium, giving them clean sea-water, seaweed, and the small shrimps on which they feed.
In our lesson on fish-nurseries we saw how the Sea-stickleback, Sand Goby and Pipe-fish cared for their eggs or young ones. These three fish are often to be found by the shore. As you look into the clear and still waters of a pool you may see a Pipe-fish getting its dinner. This funny creature looks more like a pencil swimming than a fish. It may be a foot in length, but its body is no thicker than a pipe-stem!
We have already seen how the male Pipe-fish carries his eggs in his "pocket." Another curious thing is his suit of armour. Instead of scales, he has hard plates all over his body. Very often you may see young Pipe-fish among Sprats and "Whitebait" in the fishmonger's shop.
Most of the little shore-fish are either Gobies or Blennies. No doubt they have to avoid the sharp eyes of Gulls and Cormorants, for they are very anxious not to be seen. Some of these rock-pool fish do not mind being out of water for hours at a time. In every way Nature has fitted them for their life between sea and shore. They have cousins in warmer seas which love to come ashore at times. This is how a traveller describes one of these foreign Gobies:--
"Though they are fish, and breathe by gills, they have a passion for the land, and during the daytime may always be seen ashore, especially where the coast is muddy. They bask in the sun, and hunt for food, raising themselves on their fleshy fins.... When pursued, they take great springs, using their tails and fins for the purpose; and if they cannot escape into the sea, they will dive down the burrow of a land-crab, or dash into a bunch of mangrove-roots." They are very wary, having eyes like swivels, to turn in all directions.
The Spotted Goby, as we have already noticed, makes a nest under a shell, and guards it until the eggs hatch. Two other Gobies are quite common in the pools of our south coast--the One-spot Goby and the Two-spot Goby. The back fin has the one spot, or two spots, from which they get their name. Though they are such mites, they have sharp teeth, as you may already know if you have caught them with your fingers!
These lively little fellows are not very easy to catch! They have a cunning way of hiding amid sand and rock, and are coloured to suit such places. One strange thing about the Gobies is their trick of anchoring themselves to a stone.
You may wonder what kind of anchor they can use. It is a simple matter, however. The fins on the stomach are pressed together to form a little disc. This acts as a strong sucker, much like that of the Sucking Fish [(p. 43)]. If the Goby wishes to stay still in one place, it presses its sucker to a stone; then it cannot be washed away by the ever-moving water.
It will live quite well in a glass tank of sea-water; someone who kept many interesting fish says of this Blenny:--
"Our little Butterfly Blenny was not often to be seen. It was using an old whelk shell for a nursery. In this broken old shell the dainty fish was able to hide, and was so nervous that we seldom saw it. But we placed some food near the hole in the shell, and were rewarded by the sight of the Butterfly's head, and its lovely eyes, each with a little movable tassel above it."
Hidden under weed and stones is another small brownish fish of the shore, the Gunnell or Butter-fish. You may turn it out of its snug hiding-place, but you will have a hard task to catch it, even in a small rock-pool, and, once caught, it slips through your fingers like an eel. Its body is eel-shaped, with a narrow fin on the back, and covered with a layer of slime. It well deserves the name of Butter-fish.
EXERCISES
1. Name three rock-pool fish. 2. Describe the Pipe-fish. 3. How does the Sand Goby anchor itself? 4. In what ways are these rock-pool fish so well fitted to live in such places?