Garden Ponds are a great way to enjoy your California backyard

Fishes For Pond And Aquarium There is one particular organ of the fish, however, that calls for more than passing notice. This is the ' swim bladder,' a long, double-lobed transparent affair, connected to the stomach at one end and the head at the other. It is filled with gases, principally oxygen and nitrogen, and its chief function is to maintain the fish's balance. This is effected by involuntary muscular pressure on the part of the fish-when the fore-end is contracted the tail part is lighter and so the head dips down ; when the posterior end is contracted then the head rises. From chills, congestion and other causes the swim bladder may be deranged and the fish will be unable to swim other than on its side, or it may lose its buoyancy, when it cannot raise itself from the bottom without an effort. On the other hand, if it becomes over-inflated the fish must float on the surface.

So much for the interior of the fish ; the exterior is too well known to require description. In the following list of fishes, where the external parts are referred to, they will be given the names most commonly used among aquarists ; in the accompanying diagram (Fig. 11) the same names are used.

All the fishes described in the following pages, unless marked with an asterisk, are sufficiently hardy to withstand ordinary winter conditions out of doors. The less hardy fishes should be removed to indoor aquariums at the commencement of the cold season.

Over ninety per cent, of the pond fishes are of the Carp persuasion and so all their fins are soft; none are spiny. The British carps fall into three main groups which may be recognised, roughly, as follows : Dorsal fin long, anal fin short-Carp and Crucian Carp. Both short-Gudgeon, Tench, Dace, Roach, Minnow and Rudd. Dorsal fin short, anal fin long-Common Bream and White Bream.

The Common Carp.
In the Middle Ages carp were bred largely for the table, most monasteries and large houses had their own fish stews, and on the Continent to-day this fish is esteemed as an article of diet. Owing to their usual dun colour they are of little interest to the pond keeper except the large specimens. The smaller kind, particularly if the water is at all greenish, may remain invisible for days. They are said to attain a great age, two hundred years old or more ; the largest specimen found in this country was three feet in length and weighed twenty- five pounds.