HUNDREDS of young people spend their vacation on or near the sea-shore, and have a good opportunity to study the wonderful habits of animal and vegetable marine life. Therefore we have undertaken to throw out a few plain hints as to the management of a salt-water aquarium, in which these interesting forms of nature can be observed to greater advantage.
We will start off with one of the small tin-frame tanks sold at a low price, or a candy jar, or a small-sized wash- tub — any vessel that will hold water, and is not of iron, tin, or copper, any one of which will poison the water.
After washing out the tank carefully, and filling it with clear sea-water, we will place in it twelve silver-shrimps (bait shrimps). At the end of two days they are dead, and you ask why did they die when they had so much water to live in. They died of suffocation, after they had breathed all the air contained in the water.
We will take out the dead shrimps, and in the same water place a good handful of ulva (sea-lettuce, sea-salad), one of the most common of all marine plants, and place the aquarium in a strong and direct sunlight, by this means exciting the ulva to work, or as it is termed, aerify the water.
In less than an hour’s time a froth will be seen forming on the surface of the water, adhering to the sides of the aquarium. Now observe the ulva closely, and from its edges and surface very fine threads of silver bubbles are pouring out and ascending to the surface. In an hour’s time the water will be thoroughly charged with air.
We will again place twelve more shrimps in the aquarium. This time they will live, and we will have established a true aquarium — an aquarium based on the self-sustaining principles of nature, wherein it will not he necessary to change the water.
Fish as well as human beings breathe air. Air is contained in all water. After the shrimps had breathed or used the air contained in the water several times over, it became unfit to sustain animal life any longer, and so they smothered: just the same as if a number of people were placed in a room, and all the doors and windows and ventilators were sealed up tight, so that no new air could enter. They, too, would suffocate in a short time and die.
All plants living in water are constantly manufacturing new and pure air for their friends and companions the fishes, particularly when under the action of sunlight.
The great secret in establishing a self-supporting aquarium is to establish a natural balance of water, fish, plants, and light, so that none of these agents is wanting in quantity.
For instance, a strong light is required to cause a healthy development of the plant life, but not direct sun- light, or the plants will be forced too rapidly, and death will soon follow.
Again, direct sunlight will increase the temperature of the water to such an extent that many of the fish will die. If the animal life is in excess of the plant life and the water contained in the aquarium, the animals will perish for want of sufficient air.
Again, if the aquarium is overstocked with plants, so that they are crowded so closely that the light fails to reach some of them, decom- position will take place, and ever3rthing will become a de- claying mass. In fact, it is only by beginning on a very modest scale, with a very few and small fish at first, and by gradually increasing the number, that a beginner can expect to succeed.
Overstocking with animal life and over- feeding are the two greatest temptations that beset the path to success for the aquariums ; but patience, perseverance, and critical observation will eventually lead to success.
The greatest care must be taken, and all shells, rock- work, sand, and plants must be washed over several times, so that no injurious substances may be introduced. Ulva, or sea-lettuce (Fig. i), is to be found in abundance in all our small bays and inlets at low tide.
For the aquarium, those specimens which are thick in texture, and of a dark-green color, only are fit for manufacturing air. Never be tempted to make use of the light -green and thin specimens, as they are not sufficiently matured, and will soon decay if placed in the tank.