WONDER OF PETS with Wally Ashcroft

THE majority of aquarists install a lighting system in their fish tanks so that they see their fish clearly. This is natural but the provision of light is much more important than that. Light is essential to life and this applies just as much to an aquarium as anywhere else.

Plants need light which helps them to absorb carbon dioxide, which in turn is broken down into sugar and starch, and used as a food source. The action of light helps plants to breathe, feed and multiply. Under the influence of light, plants give off oxygen into the water. This happens to coincide with the fish being at their most active, when their requirements for oxygen are at their highest. At the same time the plant absorbs the carbon dioxide which is breathed out by the fish. This process is reversed during darkness, when the plants give off carbon dioxide and absorb oxygen. The fish are resting during this period and therefore they use up much less oxygen.

It all seems very complicated but basically it means that plants need light to survive. Anyone who has left one of the children's toys on the lawn for a few days will have seen the effect that light starvation has on the grass. With too little light the plants would die.

Too much light can also be a problem. Green cells begin to develop and attach themselves to the rocks, plants and the sides of the tank. This is a living organism called 'Algae'. A small amount is good for the fish as it is a good source of vegetable food. Too much will spoil the look of the tank and can be harmful. It may seem a contradiction in terms but in certain circumstances, too much light can cause the plants to die from lack of light. Confused? I'm not surprised. The explanation is that the green algae can cover the plant and grow so thickly that the light cannot get to the leaves. The correct amount of light is a major factor in keeping an aquarium clear and clean. The plants will grow happily and there will be no extensive growth of algae. It is difficult to lay down hard and fast rules, as to the ratio of plants to light, in order to achieve this balance. If you can imagine a tank full of plants receiving the correct amount of light and then you remove half of the plants.

There will then be too much light and an excess of algae will develop. If the amount of plants is doubled then each plant will receive only half the amount of light it needs and so growth will be stunted. The answer is to err on the side of too many plants rather than too few. You can always remove surplus plants but it is more difficult to remove the algae growth.

Light is also important to the health and development of the fish. They need light to help them to find their way round in their search for food. They are also dependant on light for their development and growth. Light also stimulates the fish to swim around and so give themselves necessary exercise. This is turn keeps their body functions regular, which is so essential in maintaining good health.

A word of warning is appropriate. In your haste to turn on the aquarium light it must be remembered that fish have no eyelids. A sudden burst of light will give them an unnecessary shock. It is better to put the room lights on for a minute or two before you turn on the aquarium lights.

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