International Journal of Aquaculture, 2018, Vol.8, No.16, 121-126
125
Table 6 Parameters W
∞
(g), k, t
o
(years) from the weight growth equation of von Bertalanffy, growth index φ’ and ω parameter for the
brown trout (
S. trutta
) from different rivers
River/Author
W
∞
(g)
k
ω
φ
t
o
r
SD
Iliyna (our data)
161
0.4978
80.15
1.17
0.4164
0.998
7.14
Chaya (Yankov, 1988)
415
0.4689
194.59
1.42
0.2268
0.996
3.87
Vacha (Yankov, 1988)
785
0.2458
192.95
1.32
-0.2896
0.996
3.62
Iskar (Yankov, 1988)
1300
0.1636
212.68
1.29
-0.7378
0.994
4.06
Mesta (Yankov, 1988)
870
0.1921
167.13
1.24
-0.4530
0.997
3.33
Struma (Yankov, 1988)
445
0.2493
110.94
1.16
-0.4164
0.996
2.69
Vit (Yankov, 1988)
250
0.3496
87.40
1.14
-0.2630
0.999
1.58
The length and weight increments of the brown trout from Iliyna River change irregularly during the years. This
indicates the presence of compensation growth (Rozdina and Raikova-Petrova, 2014). The compensation growth
is a process when initially bigger fish slow down their growth and the smallest individuals increase it. This
mechanism ensures the best possible utilization of the environment resources. Density-dependent compensation
growth in brown trout has been reported from Sundström et al. (2013).
The growth constant (k) determines how fast the fish approaches its L
∞
. Some species, most of them short-lived,
almost reach their L
∞
in a year or two and have a high value of k. Other species have a flat growth curve with a
low
k-value
and
need
many
years
to
reach
anything
like
their
L
∞
(
). The highest values of the growth constant (k) for
S. trutta
from Iliyna River indicate the high growth rate of the studied population. The fast growth rate is due to the
prevalence of two and three year old individuals and determines the relatively low asymptotic length (23.16 mm)
and weight (160.69 g) (Raikova-Petrova and Živkov, 1987; Hamwi et al., 2007). The good growth rate is
determined from the good physicochemical conditions in the river. The measured physicochemical parameters of
the water exclude anthropogenic pollution or other fluctuations in the river in the period of sampling. The
conditions are good and ensure the normal development of the brown trout in the river according to its biological
requirements. To ensure the wellbeing of the species it is recommended to keep monitoring the growth rate and
the status of the population in the studied river as well as in other rivers from the area of distribution of the species
in Bulgaria.
The changes in the parameters φ’ and ω doesn’t show clear tendency. Other studies have shown that these two
parameters are not appropriate to be used for comparison of the growth rate of freshwater fish species (Rozdina
and Raikova-Petrova, 2014).
Authors’ contributions
GR participated in the sampling, data processing, drafting the manuscript and have given final approval of the manuscript to be
published; DR have been involved in the manuscript preparation, analysis and interpretation of data; RV took part in the data
procession. All authors read and approved the final manuscript.
Acknowledgements
Sampling of the material has been done for the project “Mapping and defining the conservation status of natural habitats and
fish-Phase 1”, funded by the Operational Program “Environment”. Special thanks to Martin Iliev for the active participation during
the sampling process.
References
Bertalanffy L., 1938, A quantitative theory of organic growth, (Inquiries on growth laws. II), Human Biology, 10(2): 182-213
Freyhof J., 2011, Salmo trutta, The IUCN Red List of Threatened Species 2011: e.T19861A9050312
Gallucci V., and Quinn T., 1979, Reparameterizing, fitting and testing a simple growth model, Transactions of the American Fisheries Society, 108: 14-25
