Page:Hardwicke's Science-Gossip - Volume 1.pdf/145

In the early part of last year the rag-collecting brigade commenced its operations; and one of the most abundant articles of rubbish acquired by its members proved to be old aquaria. This fact faintly indicates two things; viz., that formerly aquaria were very common in London, and that from some cause or other, having ceased to be of interest to their owners, they have been consigned to the rubbish-heap. In many cases, probably, the loss of interest arose from want of success. With a view, therefore, of stimulating some to renew, and others to begin, the cultivation of an aquarium, we wish to give a few hints for keeping one, based upon the experience of several years. The word "we" is used by the writer because much of the experience is that of other persons; while the tanks and bowls mentioned towards the end of the paper belong to a lady friend of his.

In the first place, let the reader discard the notion that aquarium-keeping is easy, but let him be convinced that what is worth doing at all, is worth doing well, and that the more diligently the necessary conditions are considered, the greater is the probability of success. Any attempt to cultivate flowers without some knowledge of horticulture is not likely to lead to a satisfactory result; and to expect to have a healthily-stocked aquarium without some knowledge of the laws which govern the health of its tenants, is quite as futile.

The crabs, star-fishes, gobies, molluscs, annelides, &c., of our tanks so far resemble ourselves, that their health and existence depend upon the quality of the medium in which they are placed: we require good fresh air, while they require good fresh sea-water. In an aquarium the same water is usually retained as long as possible; hence it should contain within it the means of supplying the requisite gases. This is done by keeping up the growth of a little seaweed. Each little creature is constantly in abstracting from the water the gaseous and solid materials conducive to its existence and increase, and restoring to it again those which are not adapted to its nourishment. The water consequently undergoes deterioration, and if the animals are too numerous, they either die off or struggle on in an unhealthy state. Overstocking is a serious fault; but, nevertheless, is very commonly met with among aquaria-keepers. In order to keep a large stock alive, many persons introduce a large supply of weed into the tank, and force its growth so as to obtain as many air-bubbles as possible, as it is thought that the more numerous these are, the larger is the stock of other animals they will be able to keep. This, we believe, is a false principle, since the water only absorbs a certain proportion of the gases generated (chiefly oxygen), while the rest rises to the surface and escapes into the air without benefiting the inhabitants of the aquarium. Moreover, plants that are stimulated by strong light in aquaria do not appear to be the healthiest. In some special cases, as when water is made to flow in a current through shallow vessels, plants may be dispensed with, as the necessary supplies of oxygen and nitrogen are absorbed by the water from the atmosphere. The vegetation that grows spontaneously in the aquarium is much more likely to thrive than such as has been introduced. Whether the water is stationary or flowing, shallow vessels are preferable to deep ones, as they will support a larger amount of life for the same area, and the creatures can be more easily seen and fed. The increased capability of maintaining life is owing to the more efficient aëration of the water, there being a smaller bulk of water to the same extent of aërially-exposed surface and of growing vegetation.

The regulation of the temperature is another important point. The seas off the British coast fluctuate between 38° and 60° F., but in tanks the water should not be allowed to range beyond a temperature limited by 44° and 65°. The best degree of heat is from 50° to 58°, to maintain which is one of the mot difficult, at the same time that it is one of the most important things to do. Warm water absorbs less air than cold; so that a tank may healthily support, say, twenty creatures at 58° F., but it would not do so at 80°, partly in consequence of the diminished quantity of air in the water. If, however, means be taken to ensure the constant aëration of the water, the temperature may be allowed to rise considerably above 58°; but there is always a large amount of risk thus incurred. If the water sinks below 44°, the anemones, &c., do not expand as usual. Variation in temperature has considerable influence on the density of sea-water when in small quantities; so that this should be taken into account when fresh water is added; the density should be kept as constant as possible at 1026, an equal bulk of distilled water being equal to 1000. This can be regulated by a hydrometer, which ought to sink up to a line marked 1026 (or 26 as it is marked on some instruments).

By especial attention to temperature, which may be regulated by opening or shutting doors and windows, burning gas, partially covering the tanks with damp cloths, and adopting other means, so as to keep the thermometer within the limits we have mentioned, at the same time taking care that the temperature does not rise or fall rapidly, most of the denizens of the aquarium may be kept in a flourishing condition for prolonged periods.

The limited space at our disposal forbids our saying more at present, but we may briefly sum up thus. Do not overstock; keep the aquarium in a spot where the light does not exceed in intensity the