Although the zahrte lives in many northern and eastern European countries, it has never been introduced to the British Isles.
Looking a bit like a shallow-bodied bream, the zahrte’s body is very narrow across the back (laterally compressed), with a scale-less keel between the anal fin and the tail fin. There is another keel on the back behind the dorsal fin, with scales curving over it.
The zahrte shares many similarities with other bream. The long anal fin has 18-21 branched rays (slightly fewer than the bream) and there are small scales on the body, numbering 66-73 on the lateral line (the bream has 51-60 scales). However, it does have one fairly distinct feature which helps distinguish it from other bream. It has a small head and long, fleshy snout 25cm (10in) zahrte with a rounded, soft tip. The mouth – with horse-shoe shaped lips – is under the snout.
A colourful life-cycle
For most of the year the zahrte is greyish blue on the back, paling on the sides to an off-yellow belly. However, at spawning time the males in particular undergo a dramatic transformation. The back becomes much darker, verging on black, and the belly and ventral fins turn a deep orange. The head and front of the body of a spawning fish of either sex are covered with pearl-white spawning tubercles.
Zahrte are partly migratory. They live mainly in the lower reaches of rivers, but for part of the year move to brackish waters such as those of the Baltic Sea. They breed between May and July on gravelly or silt-free river beds – which may be as much as 350 miles upstream of where they spend the rest of the year. (No wonder they don’t grow as deep bodied as the bronze bream!)
They shed their eggs in two or three sticky batches over clean stony river beds. At first the eggs adhere to plants or stones, but they are later washed down between the stones. The 80,000-200,000 eggs are shed in several spawnings and hatch in five to ten days. After spawning the adults return downstream to deeper, slower-flowing sections of the river.
A bottom-living fish, the zahrte feeds on the insects, crustaceans and worms that live there too. Bloodworms, mayfly and caddis larvae, freshwater shrimps, tubifex worms and river bed plant life all form part of its diet.
Six of one
Eastern European fishery workers claim to recognize six subspecies of zahrte. But it is unlikely that there is any major biological variation between them. The only really different type is found in the Sea of Azov basin in the Ukraine — it is rather smaller and lays less eggs than other zahrte.
Several isolated stocks of zahrte also appear to be native to the sub-alpine lakes of southern Germany and Austria. Under pressure, the zahrte has proved to be very adaptable and can survive in man-made lakes – provided it can move into feeder streams to spawn.
Although sometimes taken by anglers, it is not a major sporting fish. It is caught on a small scale, however, by commercial fishermen with long lines, nets or traps. Despite its many bones, the flesh is considered a local delicacy.