Certain fish ailments, if caught in time, lend themselves to treatment ; at the first sign of indisposition the cause should be sought out, if possible, and remedied and the necessary treatment applied.

Most of the ills to which a fish is liable arise from unhygienic conditions in the aquarium or pond ; lack of oxygen from overcrowding or other causes ; polluted water from uneaten food, decayed plants, etc. ; insufficient green food ; sudden changes in temperature ; extreme pH changes-from being too acid the water becomes too alkaline, or vice versa ; from parasites and infectious diseases introduced by new fishes or by molluscs or plants from wild ponds or streams, and, in the pond, the accidental introduction of patent fertilizers and so forth.

A healthy fish is less liable to infection than is a fish that is not living in good surroundings ; it is able to withstand many of the ills that fall to its weak relations. It is well to examine pond and aquarium periodically and to keep a look-out for unusual movement or deportment in the fishes. The principal signs of sickness in a fish are a drooping of the dorsal fin and a lack of energy in the tail ; all the fins, in fact, seem to lack interest in their job and are listless. This is the first symptom, usually, and if treated at this stage the fish may recover. Later and more ominous symptoms are a loss of balance and inability to maintain a position in mid-water ; the fish will lie on its side on the bottom or float in a similar position on the surface.

If there is nothing to indicate the exact nature of the complaint, then the aquarist's panacea for all fishy ills must be used, that is to say, the ' salt bath.'

Some complaints are particularly manifest, tumours, for example, and fungus. Some may be cured by operative treatment-cysts, tumours and certain cerebral derangements- but these are the province of the specialist, and unless a fish is extremely valuable, or is suffering from a really interesting ailment, it is best to destroy the fish at the onset. A number of complaints are fatal and even if taken in hand from the beginning nothing can be done. Such a complaint is Black Fungus, which appears as black fluffy spots over the body, especially the gill region.