EUTROPHICATION CONTROL OF
TSALMON RESERVOIR BY THE
CICHLID FISH TILAPIA AUREA
H. LEVENTER
Mekoroth Water Co., Water Quality Department, Bnei-Brak Laboratory, Israel
INTRODUCTION
A great part of the algae and detritus in water introduced into artificial reservoirs sinks
to the reservoir bottom, decays and supports the further growths of algae. This has been
observed to occur in a number of artificial reservoirs of Israel's national water system
(INWS), which carries annually about 360 million cubic meters of Lake-Kinneret water to
the southern part of the country. A characteristic feature of Lake Kinneret is the annual
"bloom" of alga Peridinium cinctum (Dinoflagelatae group), which regularly takes place
during the period of February to June. In spring and early summer the bottom becomes
covered with the blue-green alga Oscillatoria chalybea (Leventer 1971). This alga, during
its growth and decay, imparts to the water objectionable taste and odour, which, in the
period of 1966 to 1970 became a serious nuisance in its use for drinking (Leventer and
Eren 1970).
To prevent "the bloom" of the blue-green alga Oscillatoria chalybea over the bottom
of reservoirs, ways to reduce the concentration of organic matter in the sediments were
sought. The method chosen was to populate the reservoirs with suitable fish that subsist
mainly on decomposing matter and detritus.
In recent years this practice has been spreading of using fish to reduce algae in water
and eliminate submerged plants (Avault 1966). To reduce the amount of algal growth the
aid is enlisted of the Silver carp, Hypophthalmichthys molitrix, and to combat submerged
plants, the Grass carp, Ctenopharyngodon idella. Both species have their specific food
requirements, as distinct from the various varieties of the Tilapia group that are able to
modify their food habits according to available food, including algae, plants and detritus.
Hickling (1961), who describes the food habits offish of the Tilapia group, points out
that the species Tilapia nilotica picks its food from the lake bottom and consumes organic
matter and bacteria. In Israel Tilapia aurea, which is related to Tilapia nilotica and
resembles it in its characteristics, is to be found.
Tilapia aurea was introduced into one of the artificial reservoirs of the Israel national
water system — the Tsalmon reservoir — in 1969. The present study is the result of
observations on the development of these fish, their food habits and their effect on the
reservoir bottom. A comparison was made between the conditions which obtained in the
reservoir in 1968, when the bottom abounded with the blue-green alga Oscillatoria
chalybea, and the conditions found in 1971.
THE RESERVOIR
The Tsalmon reservoir is one of 12 artifical reservoirs of the Israel national water
system. Its area is 20 hectares, its maximum depth 4.5 m. and its capacity 800,000 cubic
meters of water. Through this reservoir an amount of 360 million cubic meters of water
217
TSALMON RESERVOIR BY THE
CICHLID FISH TILAPIA AUREA
H. LEVENTER
Mekoroth Water Co., Water Quality Department, Bnei-Brak Laboratory, Israel
INTRODUCTION
A great part of the algae and detritus in water introduced into artificial reservoirs sinks
to the reservoir bottom, decays and supports the further growths of algae. This has been
observed to occur in a number of artificial reservoirs of Israel's national water system
(INWS), which carries annually about 360 million cubic meters of Lake-Kinneret water to
the southern part of the country. A characteristic feature of Lake Kinneret is the annual
"bloom" of alga Peridinium cinctum (Dinoflagelatae group), which regularly takes place
during the period of February to June. In spring and early summer the bottom becomes
covered with the blue-green alga Oscillatoria chalybea (Leventer 1971). This alga, during
its growth and decay, imparts to the water objectionable taste and odour, which, in the
period of 1966 to 1970 became a serious nuisance in its use for drinking (Leventer and
Eren 1970).
To prevent "the bloom" of the blue-green alga Oscillatoria chalybea over the bottom
of reservoirs, ways to reduce the concentration of organic matter in the sediments were
sought. The method chosen was to populate the reservoirs with suitable fish that subsist
mainly on decomposing matter and detritus.
In recent years this practice has been spreading of using fish to reduce algae in water
and eliminate submerged plants (Avault 1966). To reduce the amount of algal growth the
aid is enlisted of the Silver carp, Hypophthalmichthys molitrix, and to combat submerged
plants, the Grass carp, Ctenopharyngodon idella. Both species have their specific food
requirements, as distinct from the various varieties of the Tilapia group that are able to
modify their food habits according to available food, including algae, plants and detritus.
Hickling (1961), who describes the food habits offish of the Tilapia group, points out
that the species Tilapia nilotica picks its food from the lake bottom and consumes organic
matter and bacteria. In Israel Tilapia aurea, which is related to Tilapia nilotica and
resembles it in its characteristics, is to be found.
Tilapia aurea was introduced into one of the artificial reservoirs of the Israel national
water system — the Tsalmon reservoir — in 1969. The present study is the result of
observations on the development of these fish, their food habits and their effect on the
reservoir bottom. A comparison was made between the conditions which obtained in the
reservoir in 1968, when the bottom abounded with the blue-green alga Oscillatoria
chalybea, and the conditions found in 1971.
THE RESERVOIR
The Tsalmon reservoir is one of 12 artifical reservoirs of the Israel national water
system. Its area is 20 hectares, its maximum depth 4.5 m. and its capacity 800,000 cubic
meters of water. Through this reservoir an amount of 360 million cubic meters of water
217