There are in excess of 20,000 species of fish in nature, and most of these are marine-based. A small number are freshwater fish, and only a tiny number of these are suitable for keeping in ponds. Nevertheless, of the few species available to us, there is a huge range of hybrids, shapes, colours, habits and sizes. And the good news is that every few years a new type of fish, or strain of fish, becomes available to the pond-keeper.
The common goldfish It is said that the common goldfish is the best known fish in the world and we can all instantly recognize it. It is fairly long-lived fish – 15 years is not unusual – and millions are bred annually by fish farms, which also makes them quite cheap to buy.
Originally from China and parts of Siberia, the goldfish is a hardy breed, able to withstand a range of temperatures from above 30C down to practically freezing. As a child I well remember the cold British winter of 1963. We had about eight goldfish in a large metal water tank in the greenhouse. The water froze solid, even under glass, all bar about three inches at the bottom. They were probably iced up for three or four days in total but, by speedily defrosting the ice, we managed to save most of the fish.
Goldfish can grow up to about 30cm (12in) from head to tail, if the conditions are right and the pool large enough. Fancy varieties are usually considerably smaller. The ‘normal’ goldfish is short-finned, usually orange but also in other single colour variations (although curiously not in the olive green that is the natural colour of its ancestors). Centuries of selective breeding have produced over 100 ‘official’ varieties of goldfish.
Golden orfe These, also known as the ‘ide’ fish, are perfect for larger ponds – with a minimum surface area of 4m2 (43 sq ft ). In the wild the orfe is silver, but the golden form has been bred for use in garden ponds, along with blue and marbled variants. They are native to various parts of Northern Europe, particularly the River Danube. They are fast movers, staying near the surface of the water – a very obliging form of behaviour as far as humans are concerned.
Orfe are usually sold as specimens of 8-10cm (3-4in) long, but in time they will reach 45cm (18in) if conditions are right. They need to swim in water that is oxygen-rich and for this reason they seem to enjoy the splashes from fountains and waterfalls. They can suffer when the oxygen runs low, for instance during dull, thundery weather.
BREEDING: in late spring the female scatters her eggs among fine-leaved water plants. Hatching takes place in around 20 days.
Golden tench This fish, which in the wild inhabits the still waters of rivers, large ponds and even sand pits, can grow to a massive 71cm (28in), although 30-41cm (12 – 16in) is more usual for a healthy adult in a large domestic pond. Tench are excellent scavengers and feed off the muddy bottoms of the pond. Although they are very hardy fish, during particularly cold weather they will bury themselves in the mud for some protection.
The original, if you like ‘wild’ form, was the green tench but for garden pond situations the cultivated golden tench is better, as it is more decorative and more easily seen. Tench are undemanding, being able to survive in relatively acidic water (low pH), with fairly low oxygen levels. The natural food of the tench comprises various insects, worms and young shoots of water vegetation.
BREEDING: a mature female can lay up to 900,000 adhesive eggs among aquatic plants and weed in late spring and early summer. Hatching can take between six to eight days.
Golden rudd The body of this fish is actually silver, but with a golden hue. Its scales are large and rough-looking, and make identification fairly easy. In a pond situation the rudd can grow to 41cm (16in) in length, feeding on worms, insects and certain aquatic vegetation. It is found wild in slow-running rivers in most parts of Europe north of the Pyrenees.
The rudd inhabits the surface and midwater section of the pond, and associates well with other fish, particularly orfe.
BREEDING: a large female rudd can lay as many as 200,000 adhesive eggs during spring and early summer. Hatching takes between 8 to 15 days, depending on the temperature.
Grass carp This species can grow to over lm (3ft) in length so a large pond is required. Although it is a fine fish, with certain excellent qualities, I hesitate to recommend it, a) because it consumes large amounts of most water plants, with relish, and b) because the larger fish can also leap, so it is not unusual for them to jump out of the pond and perish. In its favour, most grass carp kept in ornamental pools are albinos, which are particularly attractive against dark-sided ponds, and they will actually consume quantities of unwanted vegetation, including duckweed and algae.
BREEDING: this fish needs a temperature of around 27-29C to spawn, so is unlikely to breed in the confined ponds of temperate zone gardens (which, bearing in mind their eventual size, is quite possibly a relief to know).
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