218
H. Leventer
passes annually. The reservoir can be viewed as a wide river which carries water that stays
in it for a brief period of between 4 and 24 hours - a stay sufficient for most algae,
minute organisms and detritus to sink to the bottom. The source of the water is Lake
Kinneret from which the water travels through open canals having a length of 17
kilometers.
The Tsalmon Reservoir was first put into operation in 1964. Originally its bottom
consisted of basalt rocks, but gradually became covered with sediments that in 1971
reached a thickness of 3 to 6 cm. The sediments accumulated in the period of 1966 to
1968 contained 9.5 to 24.1 percent of organic matter, 0.69 to 1.28 percent of nitrogen,
0.24 to 0.59 percent of total phosphorus and 0.07 to 0.36 percent of hydrogen sulfide.
The minimum day temperature in January-February is 14°C and the maximum in
August-September, 27°. Transparency of the water is high during most parts of the year,
and the Secchi disc is visible down to 2.5 — 3.0 m., while the maximum depth, as stated,
is 4.5m. The water is low in phosphorus and nitrogen content, except in
January-February, after the disappearance of the thermocline in Lake Kinneret. During
that period the maximum concentration of nitrogen reaches 0.97 ppm. and of
phosphorus 0.029 ppm.
WORKING METHOD
Taking fish sample. For taking fish samples from the lake monofile nylon nets were
used with 72 mm. clear opening. These nets are suitable for catching the fish by daytime,
lifting them 15 to 30 minutes after spreading. The size of the net mesh permits catching
fish weighing 100 g and over. When brought up, the fish were weighed and the contents
of their digestive tracts removed for qualitative and quantitative examination.
Chemical analysis. Samples of sediment were taken from the reservoir bottom with an
Eckman bottom grab. They were from the whole layer accumulated during the years to
the thickness of 3 to 6 cm. In the sediments, as well as in the digestive tract of the fish,
the amount of organic matter was analyzed by oxidation with dichromate and nitrogen
by the Kjeldahl method.
Samples of water for dissolved oxygen determination were taken by a Kemmerer
sampler from three points in the reservoir at 0.5m. above the bottom.
Analysis of algae and bacteria. Algae samples were taken for analysis from three
depths: 0-50 cm. above the bottom, halfway down the water depth, and the top layer of
the water. Counting of the algae was carried out by the Standard Methods (1965) and the
results expressed as ASU/ml, where the ASU is a unit of 400 μ. A count was also made of
the number of Peridinium algae in the contents of the digestive tract of the fish, and the
results expressed as the number of cells per gram of wet material.
Analysis of coliform bacteria was made by the Standard Methods, and the results of
water analysis were given as MPN/100 ml, whereas the count in the sediments and the
contents of the digestive tracts of the fish was given as MPN/g of wet material.
THE FISH POPULATION
(a) Characteristics of Tilapia aurea. Tilapia aurea is a member of the Cichlidae family,
which numbers some 600 fish varieties. T. aurea reaches sexual maturity and reproductive
H. Leventer
passes annually. The reservoir can be viewed as a wide river which carries water that stays
in it for a brief period of between 4 and 24 hours - a stay sufficient for most algae,
minute organisms and detritus to sink to the bottom. The source of the water is Lake
Kinneret from which the water travels through open canals having a length of 17
kilometers.
The Tsalmon Reservoir was first put into operation in 1964. Originally its bottom
consisted of basalt rocks, but gradually became covered with sediments that in 1971
reached a thickness of 3 to 6 cm. The sediments accumulated in the period of 1966 to
1968 contained 9.5 to 24.1 percent of organic matter, 0.69 to 1.28 percent of nitrogen,
0.24 to 0.59 percent of total phosphorus and 0.07 to 0.36 percent of hydrogen sulfide.
The minimum day temperature in January-February is 14°C and the maximum in
August-September, 27°. Transparency of the water is high during most parts of the year,
and the Secchi disc is visible down to 2.5 — 3.0 m., while the maximum depth, as stated,
is 4.5m. The water is low in phosphorus and nitrogen content, except in
January-February, after the disappearance of the thermocline in Lake Kinneret. During
that period the maximum concentration of nitrogen reaches 0.97 ppm. and of
phosphorus 0.029 ppm.
WORKING METHOD
Taking fish sample. For taking fish samples from the lake monofile nylon nets were
used with 72 mm. clear opening. These nets are suitable for catching the fish by daytime,
lifting them 15 to 30 minutes after spreading. The size of the net mesh permits catching
fish weighing 100 g and over. When brought up, the fish were weighed and the contents
of their digestive tracts removed for qualitative and quantitative examination.
Chemical analysis. Samples of sediment were taken from the reservoir bottom with an
Eckman bottom grab. They were from the whole layer accumulated during the years to
the thickness of 3 to 6 cm. In the sediments, as well as in the digestive tract of the fish,
the amount of organic matter was analyzed by oxidation with dichromate and nitrogen
by the Kjeldahl method.
Samples of water for dissolved oxygen determination were taken by a Kemmerer
sampler from three points in the reservoir at 0.5m. above the bottom.
Analysis of algae and bacteria. Algae samples were taken for analysis from three
depths: 0-50 cm. above the bottom, halfway down the water depth, and the top layer of
the water. Counting of the algae was carried out by the Standard Methods (1965) and the
results expressed as ASU/ml, where the ASU is a unit of 400 μ. A count was also made of
the number of Peridinium algae in the contents of the digestive tract of the fish, and the
results expressed as the number of cells per gram of wet material.
Analysis of coliform bacteria was made by the Standard Methods, and the results of
water analysis were given as MPN/100 ml, whereas the count in the sediments and the
contents of the digestive tracts of the fish was given as MPN/g of wet material.
THE FISH POPULATION
(a) Characteristics of Tilapia aurea. Tilapia aurea is a member of the Cichlidae family,
which numbers some 600 fish varieties. T. aurea reaches sexual maturity and reproductive