Beautifully coloured with golden (and sometimes silver) flanks and a green-black back, the zander – a streamlined predator – is a member of the perch family. It has dark bars along its back, and like most freshwater fish it has a white underside and two dorsal fins. The front fin, which the fish can raise at will, is spiny.
A particular feature of the fish is its large eyes, adapted especially for seeing prey in coloured water or at night. A zander has ‘glassy’ eyes because there is a layer of pigment (called the tapetum lucidum) in the retina which helps it absorb light.
Its mouth, filled with sharp, fang-like teeth, is large and easily capable of devouring the small fish which are the zander’s main prey.
A foreign fish
The zander is not a native of the British Isles. It came originally from eastern Europe but is now widespread in Germany, Holland and France. In 1878 the ninth Duke ofBedford introduced 23 zander from Germany to the Woburn Abbey lakes. They remained localized until 1963 – when 97 were released into the Great Ouse Relief Channel in Norfolk. Since then they have spread all over eastern England, moving into many fens, rivers and lakes.
It goes without saying that the zander, a shoaling fish, is highly adaptable. It thrives in large, slow-flowing fen drains and rivers. But it doesn’t seem to do well in fast-flowing, clear rivers or in shallow waters where the oxygen content is low. Coloured waters and even tidal river stretches (where the salinity is high) produce many zander. In stillwaters you can find it during the day near drop-offs or holes because it avoids intense light.
What makes zander exceptionally efficient hunters is that they sometimes gather in a pack to feed on small fish (usually at dawn, dusk and during the night). The zander chase after the fish, grabbing them from behind (often by the tail) and swallowing them.
Because other species cannot see as well in murky water or at night, the zander have a clear advantage. They feed on worms and leeches as well as small fish such as roach.
The spread of zander from 1968 coincided with the disappearance of small fish from many Norfolk rivers and drains. The zander received the blame. Many anglers believe, however, that industrial dumping and fertilizer run-offs were the main reasons for the decline.
Zander usually spawn between April and June. A group gathers over stones or gravel, and the mature females dig a hollow in the gravel, lay about one to two million eggs and then guard them until they hatch. The males also protect the fry.
After hatching, the larvae live off their yolk sacs, reaching about Van (6mm) long after about a week. When the yolk sac is used up, the young eat plankton and insect larvae. Zander begin feeding on other fish at the age of three months – or when they are about 4in (10cm) long.