358
M. von Lukowicz et ai.
l.
The tench (Tinca tinca Linnë) belongs to the cyprinid family and has a wide—
spread distribution in Europe, except in the very northern parts. It is
also found in the near East and western Siberia (Anwand, l965). Furthermore,
it was introduced into Africa, Australia, Southeast Asia and North America
where it has been partly naturalized. For a long time, tench has been the
most importang by—fish in conventional pond carp farming. Although it has
tiny intermuscular bones, it is esteemed for the table because of its lean,
palatable
meat.
At a lower production level in former times, tench was a suitable
complementary production to carp culture in ponds. Due to the increment
of carp yield by intensified monoculture of species and age classes, tench
culture became retrograde in the last decades. In recent years, there has
been a growing interest in tench culture as fish farmers became increasingly
aware
that polyculture has some advantages over mono-species production. An
important incentive to a higher production of tench arose from the demand to
stock open waters for angling purposes with a valuable fish that would stand
even
poor water quality.
2. Biological characteristics and habits
The tench has a thickset body and a terminal mouth with a short barbel at
the corner on each side.
Its scales are deeply embedded in a thick, slimy
skin. The back and sides are dark to light olive green, the belly is paler,
and the rounded fins are always dark. A golden variety also exists. The
tench is a eurytherm species; its specific temperature demand is even less
pronounced than that of common carp, and it is found at l600 m above sea
level
(Bauch, l955). On the other hand, the tench stands water temperatures
over
35°C and tolerates a wide range of water quality. The pH should be
between 6.5 and 8.0; lethal values are below 5.0—4.5 and above l0.8. Koch
et al.
(l976) reported an oxygen consumption for marketable tench of 8.6 mg
of 02/kg/h
at a temperature of O°C and of l43.3 mg of 0 /kg/h at above
25°C. The level of metabolism, however, was not mentionëd. The tench is ‘
resistant to oxygen deficiency during transport and in storage ponds, but
does not stand being fished from drained ponds at high temperatures.
The tench prefers shallow ponds with a muddy bottom and abundant submerged
vegetation. It utilizes about the same natural food resources as common
carp. However, being a bottom dweller, at least when one or more summers
old, it tends to take up mainly benthic invertebrates. The tench diet
includes mussels, snails, worms, crustaceans and insect larvae as well as
algae and detritus. Its preference for the snails, Bithynia tentaculata
and Valvata piscinalis, is well known
Common supplementary feeds like grains or lupin are also consumed by tench,
but the food conversion rate is less favourable than in carp (Heuschmann,
l939). The
use
of buoyant carp pellets for intensive production of tench
did not give good results; the food conversion rate was twice as high
($:l)
as
in
carp (Pichler—Semmelrock, l985). However, in commercial ponds,
bigger tench greedily take up pelleted feed from demand feeders (pendulum
M. von Lukowicz et ai.
l.
The tench (Tinca tinca Linnë) belongs to the cyprinid family and has a wide—
spread distribution in Europe, except in the very northern parts. It is
also found in the near East and western Siberia (Anwand, l965). Furthermore,
it was introduced into Africa, Australia, Southeast Asia and North America
where it has been partly naturalized. For a long time, tench has been the
most importang by—fish in conventional pond carp farming. Although it has
tiny intermuscular bones, it is esteemed for the table because of its lean,
palatable
meat.
At a lower production level in former times, tench was a suitable
complementary production to carp culture in ponds. Due to the increment
of carp yield by intensified monoculture of species and age classes, tench
culture became retrograde in the last decades. In recent years, there has
been a growing interest in tench culture as fish farmers became increasingly
aware
that polyculture has some advantages over mono-species production. An
important incentive to a higher production of tench arose from the demand to
stock open waters for angling purposes with a valuable fish that would stand
even
poor water quality.
2. Biological characteristics and habits
The tench has a thickset body and a terminal mouth with a short barbel at
the corner on each side.
Its scales are deeply embedded in a thick, slimy
skin. The back and sides are dark to light olive green, the belly is paler,
and the rounded fins are always dark. A golden variety also exists. The
tench is a eurytherm species; its specific temperature demand is even less
pronounced than that of common carp, and it is found at l600 m above sea
level
(Bauch, l955). On the other hand, the tench stands water temperatures
over
35°C and tolerates a wide range of water quality. The pH should be
between 6.5 and 8.0; lethal values are below 5.0—4.5 and above l0.8. Koch
et al.
(l976) reported an oxygen consumption for marketable tench of 8.6 mg
of 02/kg/h
at a temperature of O°C and of l43.3 mg of 0 /kg/h at above
25°C. The level of metabolism, however, was not mentionëd. The tench is ‘
resistant to oxygen deficiency during transport and in storage ponds, but
does not stand being fished from drained ponds at high temperatures.
The tench prefers shallow ponds with a muddy bottom and abundant submerged
vegetation. It utilizes about the same natural food resources as common
carp. However, being a bottom dweller, at least when one or more summers
old, it tends to take up mainly benthic invertebrates. The tench diet
includes mussels, snails, worms, crustaceans and insect larvae as well as
algae and detritus. Its preference for the snails, Bithynia tentaculata
and Valvata piscinalis, is well known
Common supplementary feeds like grains or lupin are also consumed by tench,
but the food conversion rate is less favourable than in carp (Heuschmann,
l939). The
use
of buoyant carp pellets for intensive production of tench
did not give good results; the food conversion rate was twice as high
($:l)
as
in
carp (Pichler—Semmelrock, l985). However, in commercial ponds,
bigger tench greedily take up pelleted feed from demand feeders (pendulum