Are there one or two stocks of Scoranza bleak - Alburnus scoranza Bonaparte, 1845 in Lake Skadar (Montenegro) - Research Article

Ecologica Montenegrina 40: 80-92 (2021)
 This journal is available online at: www.biotaxa.org/em
 http://dx.doi.org/10.37828/em.2021.40.7

 Are there one or two stocks of Scoranza bleak - Alburnus scoranza
 Bonaparte, 1845 in Lake Skadar (Montenegro)

 DRAGO MARIĆ1* & KATARINA BURZANOVIĆ2
 1Department of Biology, Faculty of Sciences, University of Montenegro, P.O. Box 328, 20000 Podgorica, Montenegro
 E-mail: dragomrc@yahoo.com
 2
 Natural History Museum of Montenegro, Trg vojvode Bećir bega Osmanafića 16, 20000 Podgorica, Montenegro.
 E-mail: kburzanovic@gmail.com
 *Corresponding author

 Received 30 January 2021 │ Accepted by V. Pešić: 9 March 2021 │ Published online 15 March 2021.

Abstract
This paper provides the first comprehensive information on the Length-Weight Relationship (LWR) of Scoranza bleak
(Alburnus scoranza) from the Lake Skadar. The results of the study showed that LWR was different in young and older
individual fish. We concluded that no single regression would adequately describe the length-weight relationship for
Scoranza bleak in the winter period. Small fish, up to one year old, have positive allometric growth whereas older and
larger, negative. The results of this study show that the animals grow equally in the same pattern in both localities
(Raduš and Karuč) which shows that there are no two stocks as it was assumed in the past. The condition factor in
young Scoranza bleaks was lower than in the elderly. Condition factor decreased significantly during the winter period
in older specimens. Based on this, we conclude that Scoranza bleak during the winter is poorly fed/starved, which
causes a decrease in the condition factor.
 Analysis of the total sample, of any species, cannot show by what rule the population grows, if infrapopulation
variability is present, because the studied value will depend on the number of individual subgroups. If no infra-
population variability is found, the required parameter for the entire population can be calculated. In order to determine
population variability, multiple groups must be singled out. Preferably, the number of stratified samples should be at
least 6 so that correlation-regression analysis can be performed. In stratified samples, the number of individuals should
be between 30-40, for any parameter, in order to compare their mean values. The results of the study show that 50
individuals are sufficient for accurate determination of LWR (or and b, is a constant coefficient and b is the slope of
the curve.), when it is determined that there is no intrapopulation variability.

Key words: variability, length-weight relationship, conditioning factor Raduš, Karuč, Montenegro.

Introduction

The Scoranza bleak, Alburnus scoranza Bonaparte, 1845, like most species (i.e., carp, nase, goldfish, chub,
etc.), belonging to the family Cyprinidae has been intensively studied because of its importance to commerce

Ecologica Montenegrina, 40, 2021, 80-92

MARIĆ & BURZANOVIĆ

and fisheries (Drecun & Miranović, 1962; Ivanović, 1965; Stein et al. 1975). The Scoranza bleak is endemic
to the Southeastern Adriatic Ecoregions (Marić, 2019; Pešić et al., 2020). According to Marić (1995) and
Talevski et al. (2009) the Scoranza bleak inhabits only Ohrid – Drim – Skadar sistem. This species is the
most economically important species but in five last decades statistically significant decrease in abundance
was recorded in Lake Skadar (Marić, 2018).
 There are a number of papers devoted to the life-history traits, catch, place and method of fishing of
A. scoranza (Marić & Kažić, 1990; Burzanović & Marić, 2017). According to Ivanović (1965), the Scoranza
bleak in Lake Skadar performs significant migrations – in summer it is dispersed throughout the lake and in
winter it migrates to sublacustric springs. It feeds very little in these springs during the winter. Marić &
Kažić (1990) showed that the number of Scoranza bleaks is different in sublacustric springs during the
winter period, as well as the diversity of other fish species in these springs differs significantly. This affects
the choice of fishing gear, fishing time, etc. During the rest of the year, Scoranza bleak is not fishing
commercially, because it is scattered throughout the lake (not in a flock), so there is almost no data from that
period (except for spawning) because of lack of a comprehensive research. Outside sublacustric springs,
larger quantities of Scoranza bleak speciemens can only be caught during migration and spawning
periods. Almost all data published on this species were based on the samples collected during autumn and
winter, especially from sublacustric springs in which it is collected during the cold period (Drecun & Ristić,
1964; Marić, 2019). From this period (autumn-winter), the growth of Scoranza bleak from several
sublacustric springs was studied in the past and it has been showed by Coble & Knežević (1981) that there
are two growth patterns, positive allometry and isometry. The latter authors assumed that this was a
consequence of the existence of two stocks of this species in Lake Skadar. So far, detailed studies of the
length-weight sample of fish species growth from the Skadar Lake basin have not been conducted, and the
available data refer either to a small number of specimens or to a particular phase of the life cycle (Milošević
& Marić, 2012; Milošević et al., 2012; Marić & Rakočević, 2014).
 In addition to several applications of weight–length relationships (WLR) in fish biology, knowledge
of these relationships is useful for the prediction of the weight from the length values as an indication of the
fish condition or for fish stock assessments (Petrakis & Stergiou, 1995; Froese & Pauly, 2006; Vaslet et al.,
2008). The importance of WLR has been extensively documented (Froese, 2006). This method requires the
length and number of individual fish in situ while the total biomass is determined empirically by applying the
established LWR parameters. Length and weight measurements along with age data can provide information
on the stock composition, age at maturity, life span, mortality, growth and production (King, 1996; Diaz et
al., 2000; Milošević & Marić, 2012; Marić & Rakočević, 2014). The LWR of fishes is useful in assessing the
relative well-being of the fish population. It is important in estimating the standing stock biomass, as well as
in comparing the ontogeny of fish population from different regions (Petrakis & Stergiou, 1995). Length-
weight relationship parameters are often used as an indicator of fatness and general well-being or of gonad
development of fish and are useful for between region comparisons of life histories of a specific species (Le
Cren, 1951; Wotton, 1990).
 The condition factor (K) gives information when comparing two populations living in certain
feeding, density, climate, and other conditions; when determining the period of gonad maturation; and
when following up the degree of feeding activity of a species to verify whether it is making good use of
its feeding source (Weatherley, 1972). The morphometric relationships between length and weight
(LWRs) can be used to assess the well-being of individuals and to determine possible differences between
separate unit stocks of the same species (King, 2007). In addition, they may also help to determine
whether somatic growth is isometric or allometric (Ricker, 1975), as well as to describe seasonal
variations of growth within species (Bobori et al., 2010).
 The aim of this study was to evaluate the length-weight relationship and condition of the native
Scoranza bleak population from Lake Skadar. In this paper we want to show that only a detailed study
(multiple samples and a large number of specimens from all age categories) can provide accurate data.
Consideration of the life-history strategies of Scoranza bleak should be of great significance for the fisheries
management, restoration and monitoring.
 This paper provides the first comprehensive information on the Length-Weight Relationship (LWR)
of Scoranza bleak from the Lake Skadar, in order to determine whether there is there one or two stocks of the
latter species in this lake.

Ecologica Montenegrina, 40, 2021, 80-92 81

ARE THERE ONE OR TWO STOCKS OF SCORANZA BLEAK IN LAKE SKADAR

Materials and Methods

Area and habitat study. Lake Skadar is situated on the border of Montenegro and Albania (two thirds of the
lake belongs to Montenegro, one third belongs to Albania). Lake Skadar is a karst lake created by inundation
of a karstic field. It is situated between 19o 15' of eastern geographical longitude and 40o 10' of northern
geographical latitude, at the very south of the Republic of Montenegro, With the surface area that fluctuates
seasonally from approximately 370 to 540 km2 and water level also varies seasonally from 4.7 to 9.8 m
above sea level (Pešić et al., 2018). Lake Skadar is the largest lake on Balkan Peninsula Its shape is
elongated oval with peak width of circa 14 km at average water level (Figure 1). The lake extends in the
NW-SE direction, and it is approximately 44 km long, with the mean depth of 5 m (Beeton, 1981).

Figure. 1. Map of location of the Lake Skadar and study area. The grey oval marks indicate the four sampling sites.

 Waters from the watershed reach the lake by ground or underground water courses, through a
number of sublacustrine springs (so called “oka” – “eye”). The largest tributary of Lake Skadar is the
Morača River which brings around 62% of water, while the waters flow away from the lake into the sea by
the Bojana River; its average flowing through is over 300 m3/s. Average monthly water temperatures range
5-7 oC in winter, to 25-28 oC in summer. During the summer the transparency of lake waters is 2-3 meters,
but in winter it increases reaching up to 5 meters (Lasca et al., 1981; Petrović, 1981; Kastratović, 2018).

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MARIĆ & BURZANOVIĆ

 The southern and southwestern sides of the lake are rocky, barren and steep, having bays in which
the sublacustrine springs, are usually found. On the northern and northwestern side there is an enormous
inundated area, the boundaries of which change as water levels fluctuate. these shores are overgrown by
submersive and emerse vegetation (Myriophyllum sp., Ceratophyllum sp., Potamogeton spp., Phragmites sp.,
Trapa spp., Nymphea sp., Numphar sp. etc.), which tend to extend (Hadžiablahović, 2019). The average
chlorophyll a concentration indicates mesotrophic conditions in Lake Skadar, but during mid-summer, when
the highest phytoplankton abundance and biomass occurs, the trophic level of the lake increases to eutrophy
(Rakočević, 2018). The lake represents one of the most important center of biodiversity for Western Balkan
and South-East Europe with more than 100 species of water birds (Vizi, 2018) and 41 (34 autohtonus and 7
alohtonus) fish species (Marić, 2019). Fish are the lake’s most significant natural resource in terms of
contribution to the local economies. Annual catch in Lake Skadar is 300 tones of fish, mainly Cyprinus
carpio and Alburnus scoranza in the least decade (Marić, 2018).

Fish collection and measurements and statistical analisis. Our study was conducted in the winter period
during November to March 2012 and in November 2013 using various commercial fishing gears. A total of
1386 specimens of Scoranza bleak at Lake Skadar was caught. The study area included 3 localities at Lake
Skadar: Raduš, Karuč and Virpazar. At the locality Raduš (7 samples), the Sscoranza bleak was caught with
liftnets (kalimera-a type of stationary lift net) (885 specimens), sample from Karuč (7 samples) was caught
using 14-16 mm mesh-sized sinking gill nets - scoranza bleak gill nets (365 individuals), and sample from
Virpazar (1 samples) caught with hand nets (136 juvenile specimens). All specimens were measured for total
length (TL, in cm) and weight (W, total wet weight in g) to the nearest 0.01g by an electronic balance
immediately after collection (fresh). The total length (TL) of each fish (measured using digital caliper to the
nearest 0.01 mm) was taken from the tip of the anterior part of mouth to the end of the caudal fin.
 Data from multiple periods from the same location were considered as separate analytical units. The
LWRs then was calculated for each samples of A. scoranza using the following Le Cren (1951) equation:
W=aLb, where W is the weight of body (g), : is a constant coefficient and b is the slope of the curve. The
determination coefficient (R2) was used as an indicator of the quality of the regressions. If b = 3, growth is
isometric, if b < 3, it is negative allometric and if b > 3, it is positive allometric (Ricker, 1975; Froese, 2006).
Hence, the t-test was used in order to show significant deviation of obtained b- value in this study from the
expected isometric value (b=3). = − 3 S , where, Sb is the Standard error of the b-value, b is the slope
value of the curve estimation and Ts is the t-Test value. This analysis was performed both on the whole
sample and on the sample subdivided by sex. Because the LWR for the same fish species is often different
between adults and juveniles, the LWR was calculated separately for several length groups. The sex was
determined macroscopically by dissecting the organisms and looking directly at the gonads. The age of all
individuals from Virpazar was determined using scales.
 Fulton’s condition factor (K or CF), showing the degree of well-being of the fish in their habitat
(Froese, 2006) was calculated using the equation: K = (W/L3)x100. Which, K or CF is the Condition Factor,
W is the weight of individual of fishes and L is the total length value of individual of fishes and the factor
100 is used to bring K close to unity. The differences between sex, sites and samples were analysed by t–test
or Analysis of Variance (ANOVA). All the statistical analyses were considered at a significance level of 5%
or 1% or 0.1% (P

ARE THERE ONE OR TWO STOCKS OF SCORANZA BLEAK IN LAKE SKADAR

Figure 2. The weight–length relationship and condition factor of Scoranza bleak from Virpazar.

 Young or individuals less than 12 cm caught at the Raduš site have the same growth pattern (LWR)
as young individuals caught at the Virpazar site. The b-values were ranged from 3.36 to 3.60. The results are
given below:
 Virpazar: Length

MARIĆ & BURZANOVIĆ

 Applying the t-test, it was noticedthat the regression coefficients of both the groups mentioned above
differed significantly at 1% level. The results are given below:
 Length ≥12 cm (n= 365, all), (to 18.5cm) Y=0,0348x2.4505 R2 =0.7126 (Figure 3)
 Length ≥12 to 15.5 cm (n= 254), Y=0,0166x2.732 R2 =0.6511 (Figure 4 )

Figure 3. The weight–length relationship of Scoranza bleak from Karuč.

Locality Raduš. The results of LWR ( and b parameters and R2) of Scoranza bleak population, from locality
Raduš according to separate samples are shown in Table 2. Some data of LWR are presented in Fig. 3. No
signffcant differences (P>0.05) were found between the males and females from Raduš.

Table 2. Values of and b parameters and R2 in separate samples from Raduš.
 13.12.201 13.12. 9.01.201 30.01. 30.01. 20.02. 20.02. 4.03. 4.03. 14.03. 14.03.
 2 2012 3. 2013. 2013. 2013. 2013. 2013. 2013. 2013. 2013.
 N=136 N=145 N=46 N=49 N=101 N=84 N=66 N=67 N=83 N=80 N=50
 10-12 cm ˃12cm ˃12 cm 10-12cm ˃12 10-12cm ˃12cm 8.5-12cm ˃12cm 8.5-12cm ˃12cm

 0.0015 0.0133 0.0157 0.0130 0.0104 0.0023 0.0140 0.0150 0.0061 0.0031 0.0095
b 3.6504 2.7860 2.6995 3.6997 2.8358 3.4374 2.7707 3.5962 3.0302 3.2921 2.8530
R2 0.7186 0.8114 0.8239 0.4252 0.7164 0.9103 0.6602 0.9255 0.8517 0.8988 0.8699

 Altogether 885 fish of the length range 8.5-15.5 cm were examined. The b values from the seven
samples from Raduš were ranged from 2.6995 to 3.0302 for specimens larger than 12 cm. Based on the
current data, there were no significant deviation (P>0.05) between obtained b values of A. scoranza samples
and the b value of isometric growth (b=3), while there were a significant differences for the younger
specimens (P

ARE THERE ONE OR TWO STOCKS OF SCORANZA BLEAK IN LAKE SKADAR

 The specimens large than 12 cm from the seven samples were adjusted adequately to the length–
weight exponential (power function) model, and no signffcant differences were found between the samples
of isometric growth (P>0.01 in all cases) from the Raduš locality; therefore, the data were pooled by using
all individuals, and treating them as a single group. Length distribution of A. scoranza specimens caught at
both sampling sites (Raduš and Karuč) is given in Figure 4. Also, for Raduš, differences were statistically
insignificant between females and males (P>0.05), therefore, the data were pooled by using all individuals
(length ≥12 cm), and treating them as a single group. The results of LWRs estimation in this research (table
3) showed a high association between length growths and weight which was statistically significant in
specimens larger than 12 cm (P

MARIĆ & BURZANOVIĆ

the sampling tools. We found no significant differences in weight/length relationship of Scoranza bleak
between the studied sites, suggesting that Lake Skadar contains one stock or one homogenous population.

The condition factor of Scoranza bleak. The condition factor for the sample from Virpazar varies in the range
of 0.36 - 0.72 with an average value of 0.55 (SD = 0.06). In specimens that are older than one year, i.e. in
this case they are two years old, the condition factor varies from 0.51 to 1.34. The condition factor of
Scoranza bleak population from the studied sites is shown in Fig. 4-5.

Table 3. Values of condition faktor (CV) in separate samples from Raduš.
 P e r i o d s
 13.12.2012 9.01.2013. 30.01.2013. 20.02.2013. 04.03.2013. 14.03.2013. 9.12.2013.
 N=280 N=74 N=150 N=150 N=150 N=131 N=100
 CV 0.77 0.74 0.69 0.66 0.65 0.64 0.77

Table 4. Values of condition faktor (CV) in separate samples from Karuč.
 P e r i o d s
 13.12.2012 9.01.2013 20.02.2013. 4.03.2013. 01.11.2013 20.11.2013. 9.12.2013.
 N=120 N=74 N=40 N=30 N=87 N=101 N=71
 CV 0.93 0.7 0.67 66 1.07 0.84 0.85

 The Fulton’s condition factor of A. scoranza sampled in study area has average values between 1.07
and 0.64. Females proved to be in better condition than males, but the differences were not statistically
significant (P

ARE THERE ONE OR TWO STOCKS OF SCORANZA BLEAK IN LAKE SKADAR

Figure 7. Length and weight variability of Scoranza bleak from Raduš during the fish caught season (1 November - 14
March).

 The mean condition factor varied during season. Maximum value was obtained from November and
December; however, they were low March during the sampling period. Therefore, the average condition
factor was not calculated for all samples (Fig. 8).

Figure 8. Condition factor of Scoranza bleak from Raduš and Karuč during the fish caught season (1 Novembar - 14
March = 135 days).

Discussion

The weight–length relationship and condition factor of Scoranza bleak (A. scoranza), were studied in
specimens from Lake Skadar during the winter period. The results presented in this study contribute to the
knowledge weight-length relationship and the condition factor variability. The parameters of the LWR might
be affected by various factors including season, sex, differences in the length range of the caught specimens,
population density, sexual maturity age, habitat, food quality or quantity, fish health or environmental
conditions (Petrakis & Stergiou, 1995; Froese & Pauly, 2017; Kharat et al., 2008; Milošević & Marić, 2012;
De Giosa et al., 2014; Özpiçak et al., 2018). A number of studies about the ratio of length and weight have
been conducted on fish found in the world, but in many of these studies the length dependence was not

 88

MARIĆ & BURZANOVIĆ

analyzed (see for examples at https://www.fishbase.se/Search.php). There are only one study related to the
biology of fishes from the Skadar Lake drainage, in terms of growth related to differences in the length range
(Marić & Rakočević, 2014).
 Alburnus scoranza (Bonaparte, 1845), is an important freshwater species for comercial and
recreational fishing in Montenegro (Marić, 2018). Many studies have been carried out on Scoranza bleak in
Montenegro and other countries in the past (Coble & Knežević, 1981). The parameters for LWR and the type
of growth were estimated for the first time in A. scoranza specimens from the Lake Skadar.
 Our study reveals that there was no difference in the LWR between juveniles from Raduš and
Virpazar. On the other hand, the present study revealed that length groups of a smaller size had positive
allometric growth as compared to larger specimens that shows negative allometric growth. Our result is
consistent with Khan et al. (2012) who showed that juvenile and adult stages of a fish may exhibit
differences in the length-weight relationships owing to the changes in the body form with size, feeding habits
and factors related to reproduction.
 In fisheries practice of length-weight relationship (LWR) research is common (Froese, 2006). The
Fulton’s condition factor (CF) is a widely used parameter that helps assess the general condition of fish, their
growth, survival, maturity, and reproduction (Le Cren, 1951). In fish from Montenegrin waters, these
parameters have been poorly studied, in more detail only for C. carpio (Milošević & Marić, 2012), two
species of the genus Rutilus (Milošević et al., 2012) and S. farioides (Marić & Rakočević, 2014). Partial
studies were performed on several species from Lake Skadar collected over a long period of time, and
presented as aggregate data (e.g., Milošević & Mrdak, 2015). In the earlier period, Scoranza bleak and Carp
were investigated by Coble & Knežević (1981).
 The study of condition factor in A. scoranza during the late autumn and winter period when this
species usually migrates to sublacustric springs (Drecun & Ristić, 1964; Marić & Kažić, 1990) reveals a
statistically significant decrease in this coefficient during the studied period (R2 = 0.79). At the beginning of
the fishing season CF usually exceeds the value of 1.0, and at the end of the fishing season the value of the
latter coefficient decreases to about 0.65. At the same time, this shows that specimens lose weight during the
winter period (Fig. 7), which would mean that fish practically do not feed during this period. According to
Ivanović (1965), the Scoranza bleak from the Lake Skadar feeds very little or does not feed at all during the
winter. This research shows that through the conditioning factor, which can be easily calculated by the
analysis of live individuals, it can be determined whether the species that in this case is Scoranza bleak feed
or did not feed in studied water body for a longer period. At the same time, the above-mentioned data for
Scoranza bleak, show that they end their intensive growth as early as November and from that period annual
rings begin to form. Unlike the Scoranza bleak, C. auratus was found to feed intensively during the winter
period, but due to its nutrition which is mainly represented by detritus, it slows growth (Marić, 2000).
 The condition factor in smaller specimens of A. scoranza, one year of age, differs significantly from
larger specimens, but in larger specimens longer than 11 cm variability in relation to length and sex has not
been determined. This shows that the feeding and thus the growth of young specimens differ significantly
from the older ones, which has already been established in other species (Milošević & Marić, 2012; Marić &
Rakočević, 2014).
 The analysis of length - weight relationship (LWR) shows that individuals of A. scoranza with
different sizes have different values of the coefficient b, i.e. they have a different growth pattern. Young
specimens have positive and large negative allometry, which is especially visible in specimens larger than 12
cm. This inequality in the growth of smaller and larger specimens is also recorded in other species, although
in some species smaller specimens have positive and sometimes negative allometry (Milošević & Marić,
2012; Marić & Rakočević, 2014; Milošević & Mrdak, 2016). Analysis of samples during the winter period,
when Scoranza bleak does not feed, as already explained, shows that there are no changes in the growth
pattern. All large specimens from 7 periods, during the winter period, from the Raduš and Karuč sites have
negative allometry. This paper shown that the existence of two Scoranza bleak stocks in Lake Skadar (Coble
& Knežević, 1981) has no support. The study of the existence of different stocks is common in fish. Recent
genetic research that has been done has shown the existence of different stocks not only between rivers but
also in the same river (Anderson et al., 2007, Miettinen et al., 2020). In some lakes, as many as 4 morphs or
stocks have been found that differ morphologically in growth and nutrition (Østbye et al., 2020). Fish
polymorphism has been shown to be present in species living in deep lakes (Jonsson et al., 1998, Salzburger,
2018; Østbye et al., 2020). In Skadar Lake, however, morphological or ecological polymorphism of fish
cannot be expected, because the lake is shallow (Beeton, 1981).

Ecologica Montenegrina, 40, 2021, 80-92 89

ARE THERE ONE OR TWO STOCKS OF SCORANZA BLEAK IN LAKE SKADAR

 We assume that assumption of two stocks made by Coble & Knežević (1981) is a consequence of
differences in the length structure of Scoranza bleak in the analysed samples. In this study, A. scoranza from
some samples (which were treated as a whole) have different growth models, but separating young
specimens from the sample showed that larger specimens (≥12 cm) had negative allometry. This suggests
that in LWR analysis the age groups must be analysed separately. If it turns out that there is no infra-
population difference in the growth pattern, the required parameter for the entire population can be
calculated and compared with other populations. Unfortunately, not enough attention is paid to this problem
in the so-called “technical contribution” that is published in numerous journals where LWR data are given
mainly for the whole population and not by age. For example, LWR data calculated for the entire population
were published for several species of fish from Skadar Lake, and for the Scoranza bleaks by Milošević &
Mrdak (2016) who stated that the population from the Lake Skadar shows negative allometry as a growth
model. However, in the latter study, both small (6.3 cm and 2.2 g) and larger samples (17.9 cm and 47.4 g)
were analyzed together.

Acknowledgements
We thank two anonymous reviewere, whose constructive comments greatly improved this paper.

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