220
H. Leventer
food. From the aspect of food quality, the year can be divided into two periods. In the
first period, from February to June, the fish feed on the Peridinium cinctum alga, which
is present in the water in large quantities (see Fig. 4). During the second period, July to
January, the fish obtain their food from the reservoir bottom, which is mainly covered
with inorganic sediments, organic matter as well as with diatoms and green algae.
Qualitative and quantitative examinations were made of fish weighing from 100 to 800
g. Every kg. of fish contained 30.4 - 59.6 g. of wet food equal to 6.4 — 13.7 g. dry
material. From the chemical aspect, considerable variations were observed in the course
of the year (Fig. 1). On October 30, 1970 the organic matter represented 25% of the dry
material. This rose gradually and reached 63.4% in May 1971. During that period most of
the food consumed by the fish was composed of Peridinium algae cells. Also nitrogen
concentrations showed considerable fluctuations during the year, between 1.7 and 3.03
percent of the dry material.
mlllll
30
20
17
20
24
28
19
12
Oct.
Jan. March April
May
June July
Aug.
Fig. 1
Concentration of Organic matter in the digestive tract of the fish Tilapia aurea and in the
Sediment of Tsalmon reservoir. (Black - Intestinal contents, White - Reservoir sediment.)
From Fig. 1 it can be seen that the concentration of organic matter in the intestinal
contents of the fish was between 3 and 6 times greater than on the lake bottom.
The fish were found to utilize only 31 to 43 percent of the organic matter in their
food. An examination of 10 specimens on April 20, 1971 showed the contents of the
front portion of the digestive tract to have 51.6% of organic matter and 3.17% of
nitrogen. In the rear portion the organic content was 36.1% and nitrogen 1.99%.
An analysis of 14 specimens of July 13, 1971 showed in the front portion of the
intestinal tract 52.6% of organic matter and 3.4% of nitrogen, and in the rear portion
29.9% of organic matter and 1.8% of nitrogen.
60
55
§ 5 0
* 45
■o 40
o 35
ω
c
o 15
σ>
O 10
5|
H. Leventer
food. From the aspect of food quality, the year can be divided into two periods. In the
first period, from February to June, the fish feed on the Peridinium cinctum alga, which
is present in the water in large quantities (see Fig. 4). During the second period, July to
January, the fish obtain their food from the reservoir bottom, which is mainly covered
with inorganic sediments, organic matter as well as with diatoms and green algae.
Qualitative and quantitative examinations were made of fish weighing from 100 to 800
g. Every kg. of fish contained 30.4 - 59.6 g. of wet food equal to 6.4 — 13.7 g. dry
material. From the chemical aspect, considerable variations were observed in the course
of the year (Fig. 1). On October 30, 1970 the organic matter represented 25% of the dry
material. This rose gradually and reached 63.4% in May 1971. During that period most of
the food consumed by the fish was composed of Peridinium algae cells. Also nitrogen
concentrations showed considerable fluctuations during the year, between 1.7 and 3.03
percent of the dry material.
mlllll
30
20
17
20
24
28
19
12
Oct.
Jan. March April
May
June July
Aug.
Fig. 1
Concentration of Organic matter in the digestive tract of the fish Tilapia aurea and in the
Sediment of Tsalmon reservoir. (Black - Intestinal contents, White - Reservoir sediment.)
From Fig. 1 it can be seen that the concentration of organic matter in the intestinal
contents of the fish was between 3 and 6 times greater than on the lake bottom.
The fish were found to utilize only 31 to 43 percent of the organic matter in their
food. An examination of 10 specimens on April 20, 1971 showed the contents of the
front portion of the digestive tract to have 51.6% of organic matter and 3.17% of
nitrogen. In the rear portion the organic content was 36.1% and nitrogen 1.99%.
An analysis of 14 specimens of July 13, 1971 showed in the front portion of the
intestinal tract 52.6% of organic matter and 3.4% of nitrogen, and in the rear portion
29.9% of organic matter and 1.8% of nitrogen.
60
55
§ 5 0
* 45
■o 40
o 35
ω
c
o 15
σ>
O 10
5|