Eutrophication Control of Tsalmon Reservoir
225
High concentration of organic matter on the bottom of the reservoir, high
transparency of the water, and penetration of light to the bottom of the reservoir
encouraged the development of a rich flora there during 1966 to 1970. During the period
of April to July the dominant alga on the reservoir bottom was Oscillatoria chalybea. In
the remaining parts of the year numerous diatoms algae were found, the principal ones
being Cymbella, Navicula and Synedra. A characteristic feature of this reservoir is the
growth of algae in the benthos, whereas these usually grow in the plankton.
In 1971 there was no appearance of the blue-green alga Oscillatoria chalybea on the
reservoir bottom, and also the number of other algae was less than in 1968. The
submerged plants became acclimatized in the reservoir as from 1965 — only one year
after the reservoir was filled with water. This vegetation consisted of two varieties of
Potamogetum: P. pectinatum and P. perfoliatum. The amount of this vegetation was very
great and covered the whole reservoir bottom at a high density. During the period 1966
to 1969 growth started in May-June and reached its peak in August-September,
whereupon the plants became detached and were carried by the water to the corners of
the reservoir.
In 1970-71 there were no submerged plants in the Tsalmon Reservoir.
SUMMARY
(l)The fish Tilapia aurea has been found to be efficient in reducing the organic content of
sediment accumulating on the bottom of the Tsalmon Reservoir. They act directly by
straining Peridinium cinctum alga for their food, and indirectly by feeding off bottom
sediments.
(2)Reduction of the organic content of the bottom sediment has prevented reducing
conditions at the bottom of the reservoir and suppressed growth of the blue-green alga
Oscillatoria chalybea.
(3) Tilapia aurea prevent the growth of submerged vegetation on the bottom of the
reservoir. The resulting exposure of the bottom accelerates oxidation of the sediment.
(4)In the digestive tract of the fish fecal coliforms are abundant. Analyses have not so far
shown any increase in the concentration of coliforms in the reservoir water
attributable to the fish.
(5)The rapid increase of the fish Tilapia aurea calls for observation and control of their
numbers by the use of suitable fishing methods and by the introduction of predatory
fish.
REFERENCES,
1 AVAULT, W.J., SMITHERMAN, R.O. and SHELL, E.W., Evaluation of Eight Species of Fish for
Aquatic Weed Control. FAO World Symposium on Warm-water pond fish culture. W.M. 45117
(1966)
2 GELDREICH, E.E., and CLARKE, N.A., Bacterial Pollution Indicators in the Intestinal Tract of
Freshwater Fish. Appl. Microbiol. 14; 429 (1966)
3 HICKLING, F.C., Tropical Inland Fisheries, pp.287. Longmans (1961)
4 LEVENTER, H., and EREN, J., Taste and Odor in the Reservoirs of the Israel National Water
System. In: H.I. Shuval (ed) Development in Water Research, pp. 19-37, Ann Arbor - Humphrey
(1970).
5 LEVENTER, H., State of Oxidation at the Mud Surface in Reservoir and the Bloom of the
blue-green alga Oscillatoria chalybea. In press (1971).
6 Standard Methods for the Examination of Water and Wastewater. APHA., AWWA., and WPCF.
New York (12th ed. 1965).
225
High concentration of organic matter on the bottom of the reservoir, high
transparency of the water, and penetration of light to the bottom of the reservoir
encouraged the development of a rich flora there during 1966 to 1970. During the period
of April to July the dominant alga on the reservoir bottom was Oscillatoria chalybea. In
the remaining parts of the year numerous diatoms algae were found, the principal ones
being Cymbella, Navicula and Synedra. A characteristic feature of this reservoir is the
growth of algae in the benthos, whereas these usually grow in the plankton.
In 1971 there was no appearance of the blue-green alga Oscillatoria chalybea on the
reservoir bottom, and also the number of other algae was less than in 1968. The
submerged plants became acclimatized in the reservoir as from 1965 — only one year
after the reservoir was filled with water. This vegetation consisted of two varieties of
Potamogetum: P. pectinatum and P. perfoliatum. The amount of this vegetation was very
great and covered the whole reservoir bottom at a high density. During the period 1966
to 1969 growth started in May-June and reached its peak in August-September,
whereupon the plants became detached and were carried by the water to the corners of
the reservoir.
In 1970-71 there were no submerged plants in the Tsalmon Reservoir.
SUMMARY
(l)The fish Tilapia aurea has been found to be efficient in reducing the organic content of
sediment accumulating on the bottom of the Tsalmon Reservoir. They act directly by
straining Peridinium cinctum alga for their food, and indirectly by feeding off bottom
sediments.
(2)Reduction of the organic content of the bottom sediment has prevented reducing
conditions at the bottom of the reservoir and suppressed growth of the blue-green alga
Oscillatoria chalybea.
(3) Tilapia aurea prevent the growth of submerged vegetation on the bottom of the
reservoir. The resulting exposure of the bottom accelerates oxidation of the sediment.
(4)In the digestive tract of the fish fecal coliforms are abundant. Analyses have not so far
shown any increase in the concentration of coliforms in the reservoir water
attributable to the fish.
(5)The rapid increase of the fish Tilapia aurea calls for observation and control of their
numbers by the use of suitable fishing methods and by the introduction of predatory
fish.
REFERENCES,
1 AVAULT, W.J., SMITHERMAN, R.O. and SHELL, E.W., Evaluation of Eight Species of Fish for
Aquatic Weed Control. FAO World Symposium on Warm-water pond fish culture. W.M. 45117
(1966)
2 GELDREICH, E.E., and CLARKE, N.A., Bacterial Pollution Indicators in the Intestinal Tract of
Freshwater Fish. Appl. Microbiol. 14; 429 (1966)
3 HICKLING, F.C., Tropical Inland Fisheries, pp.287. Longmans (1961)
4 LEVENTER, H., and EREN, J., Taste and Odor in the Reservoirs of the Israel National Water
System. In: H.I. Shuval (ed) Development in Water Research, pp. 19-37, Ann Arbor - Humphrey
(1970).
5 LEVENTER, H., State of Oxidation at the Mud Surface in Reservoir and the Bloom of the
blue-green alga Oscillatoria chalybea. In press (1971).
6 Standard Methods for the Examination of Water and Wastewater. APHA., AWWA., and WPCF.
New York (12th ed. 1965).