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International Journal of Aquaculture, 2015, Vol.5, No.1 1
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5
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3
3.2 Relationship between the fecundity and the
temp of growth
The equations representing the linear growth of two,
three and four years old females are as follows:
L=8.8037+0.2427S, r=0.8; L=3.0593+2.471S, r=0.77
and L=26.36+0.0148S, r=0.08.
The equation representing the weight growth for the
two, three and four years old female fishes are as
follows: W=19.881L–302.81, r=0.97; W=21.354L–334.96,
r=0.97; W=13.629L–116.19, r=0.4.
Although no correlation was found between L-S and
L-W for the 4 years old females a positive correlation
was found between the fecundity and the coefficient
b
from the relations L-S and L-W (Figure 3 and Figure 4).
The fish fecundity declines with increasing the
linear and weight growth rate of the fishes. The
relationship between the fecundity and the coefficient
b
is: F=45382–6416.6b, r =0.8.
Figure 3 Relation between the fecundity (F) and the coefficient
b from the equation L=a+b.S
3.3 Condition factor
The value of the coefficient of Fulton for the studied
population, calculated using the gutted weight of the
individuals is about 1. For males and females the
values of K
f
are respectively 1.05 and 1.07. Condition
factor was studied also for each age group separately
for males and females and combined. Its values for the
population increase with the fish age. For males and
females by age groups the values of the condition
factor are above 1 or very close to 1 (Table 2).
Figure 4 Relation between the fecundity (F) and the coefficient
b from the equation W=a+b.L
With increasing the age, the condition of females is
decreasing and the fecundity is growing (Table 2). The
correlation between the fecundity and K
f
(calculated
using the gutted weight) is represented with the
following equation: F=234898–180246K
f
, r=0.84.
4 Discussion
Decreasing the coefficient
b
from the relationship
between the fish length and age with the years is a
sign that the temp of growth of the fishes in long term
is decreasing. This is also confirmed from the drop of
the annual length of the catches in 2011. The main
reason for the reduction of the temp of growth is the
overexploitation of the stocks of the Pontic shad. The
permanent removal of the biggest individuals from the
fish stock of the commercial fish species leads to the
size reduction of the individuals in the stock.
According to the data of the National Agency of
Fisheries and Aquaculture (personal communication)
the annual catches of the species in the Danube River
from 2004 to 2011 have declined with 3.7 times.
Table 2 Condition factor and fecundity by age in
A. immaculata
from the Bulgarian sector of the Danube River
Age
Male+Female
Male
Female
Fecundity
K
f
K
f
(gutted weight)
K
f
K
f
(gutted weight)
K
f
K
f
(gutted weight)
2
1.03
0.91
1.13
1.02
1.27
1.13
35997
3
1.075
0.93
1.17
1.06
1.27
1.10
30230
4
1.07
0.95
1.12
1.02
1.24
1.02
52467
5
1.08
0.99
1.08
0.99