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International Journal of Aquaculture, 2015, Vol.5, No.1 1
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5
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2
to the nearest 1 mm, the total weight (W) and the
gutted weight (w) to the nearest 1 g. The age was
determined by the scales at magnification of 17.5x
with Projector Dokumator, Lasergeret (Carl Zeiss, Jena).
Age-length relationships were determined by linear
regression, by the equation:
L=a+b.t
, where
L
is the
standard length and
t
is the age of the fish.
The absolute individual fecundity (F) was determined
by the weighing method. The relation between the
fecundity and the temp of growth was studied by
linear regression. The linear temp of growth was
represented from the coefficient
b
from the equation
L=a+b.S
, where
L
is the standard length in cm and
S
is the scale radius, in units.
To express the weight
temp of growth the coefficient
b
from the equation
W=a+b.L
(
L
- standard length in cm and
W
- total
weight in g) was used.
Condition factor was studied by the coefficient of
Fulton:
K
f
=(w/L
3
).100
and
K
f
=(W/L
3
).100
where
w
is
the gutted weight in g,
W
is the total weight in g, and
L
is the standard length in cm.
3 Results
3.1 Length-age relationship
It is established high relation between the fish length
and the age (Table 1). During the years the coefficient
b
was declining (Figure 1). On Figure 2 are
represented the annual fluctuations in the average
length of the catches of
A. immaculata
, from the
Bulgarian sector of the Danube River. The range of
the average length was between 20.1 cm and 26.3 cm.
Between 1962 and 2010 the average length varies
within 23.7 cm and 26.3 cm. In 2011, there is a
significant decrease in the average fish length of
the catches.
Figure 1 Changes in the coefficient b from the relationship
between the fish length and age (L=a+b.t) during the years
Figure 2 Annual fluctuations in the average length of the
catches of
A. immaculata
, from the Bulgarian sector of the
Danube River
Table 1 Regression between the standard length and age in
A. immaculata
from Danube River
Author
Year
Equation
r
n
Kolarov, 1965
1962
L=11,764+3,495.t
0,993
Kolarov, 1965
1963
L=11,963+3,37.t
0,99
Kolarov, 1965
1964
L=13,65+3,059.t
0,996
Kolarov, 1978
1971
L=11,128+3,629.t
0,992
181
Kolarov, 1978
1972
L=12,244+3,283.t
0,996
1106
Kolarov, 1978
1973
L=12,763+3,254.t
0,993
873
Kolarov, 1978
1974
L=12,648+3,39.t
0,993
988
Kolarov, 1980
1979
L=12,226+3,4383.t
0,997
Present study
2010
L=0,9678.t–21,93
0,72
134
Present study
2011
L=0,4552.t–6,1722
0,93
159