Morphological Variability and Sexual Dimorphism of Danube Crayfish Pontastacus leptodactylus Eschscholtz, 1823 from the Vrbas River

Research article

Rajko Roljić1, Vera Nikolić2, Nebojša Savić3

 

1    University of Banja Luka, Genetic Resources Institute, Bulevar Vojvode Petra Bojovića 1А, Banja Luka, Republic of Srpska, Bosnia and Herzegovina; E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2    University of Belgrade, Faculty of Biology, Studentski trg 16, Beograd, Republic of Serbia

3    University of Banja Luka, Faculty of Agriculture, Bulevar Vojvode Petra Bojovića 1А, Banja Luka, Republic of Srpska, Bosnia and Herzegovina

 

Abstract

The paper presents data on morphological variability and sexual dimorphism of Danube crayfish (Pontastacus leptodactylus) from the Vrbas River in Srbac. Crayfish were captured with hand made traps from October 2018 to May 2019. A total of 35 crayfish were caught, of which 22 males and 13 females. The dimensions of eight morphometric characteristics: body weight (W), body length (TBL), claw length (CLL), cephalothorax length (CEF), carapace width (CPW), abdomen length (ABL), rostrum length (ROL) and rostrum width (ROW) were analyzed, both in males and females. Also, for all caught specimens condition factor was determined. The results of the morphometric character measurements fit into the range of variation and represent the first data for the investigated area. By using t-test, it was noted that there are significant differences between the sexes for W, TBL, CLL, CEF, ABL and ROL, which is explained by the pronounced sexual dimorphism of Danube crayfish.

Keywords: Danube crayfish, morphometric characteristics, sexual dimorphism, Vrbas River.

Introduction

Freshwater decapod crustaceans (Astacoidea, Parasttacoidea) make up a very diverse group that inhabits different types of aquatic habitats (Crandall and De Grave, 2017). Danube crayfish, Pontastacus leptodactylus Eschscholtz, 1823 inhabits lowland and slow-flowing rivers with soft muddy bottom, estuaries, lakes, ponds, brackish waters and swamps. (Machino and Holdich, 2006) The morphometric character of crayfish are the essential criteria for determining the taxonomic status of the species. Precise crayfish taxonomy involves the application of these methods in combination with anatomical, morphological, cytogenetic, biochemical, physiological, ecological, evolutionary, and other methods (Vuković et al., 1978, Maguire 2010).

The data on the values of the morphometric characteristics of the species Pontastacus leptodactylus from many areas within their areal are scarce. This species is widespread throughout Europe, eastern Russia, and the Middle East. However, this species is absent in some countries of northern Europe, such as Norway and Sweden, and the countries of Southern Europe, Spain, and Portugal (Souty-Grosset et al., 2006). It is considered an indigenous in the eastern part of its area, but it was introduced into many western European countries (Machino and Holdich, 2006; Souty-Grosset et al., 2006). In Bosnia and Herzegovina, the species was recorded in 2005. It inhabits the Danube River Basin (the Sava River in the Brčko District and the Miljacka River upstream of Sarajevo) (Trožić-Borovac, 2011). It is spreading north where it inhabits the river Matura and the lower course of the Vrbas River downstream from Razboj (unpublished data).

Given the lack of data on Danube crayfish at the European level (Holdrich, 2002) and the complete lack of research into Astacofauna in the northern Republic of Srpska (Trožić-Borovac, 2011), the aim of this study was to investigate the Danube crayfish population for the first time (P. leptodactylus) in the Vrbas River. As preliminary studies determined the presence of this species in the lower Vrbas River, our intention was to describe its morphometric characteristics. This research aims to determine whether there are differences between the morphometric characteristics of males and females and to look at the degree of the condition of the captured individuals in order to estimate the possible pressure on the population of Danube crayfish.

 

Materials and Methods

The lower part of the Vrbas River is located at an altitude of 94 m. Riverbed width is from 60 to 80 m, and depth is from 1 to 5 m. It covers the Vrbas River flow through the open terrain, so it often changes its bed and creates meanders in some places. The bottom is muddy, with a mild drop in the bed. The riverbank area is covered with wetland vegetation, with the dominance of flood forests (Radević, 2000).

The nets and LiNi trap with baits were used to collect crayfish specimens (Westman et al., 1978). Given that the traps for crayfish hunting are selective for the size of specimen (Hogger, 1988), almost all of the hunted specimens of crayfish were larger than 70 mm (Souty-Grosset et al., 2006). All the crayfish were caught at twilight, between 06:00 p.m. and 10:00 p.m.

The values of the essential morphometric characteristics were determined in terms of the basic morphometric characteristics: body length (TBL), claw length (CLL), cephalothorax length (CEF), carapace width (CPW), abdomen length (ABL), rostrum length (ROL) and rostrum width (ROW). The parameters are determined by the values of body weight (W), Fulton's condition factor (FCF) and Decapoda crayfish (CC) constants.

Fulton’s Conditions Factor (FCF):

Where: W – total weight, TBL – total length

Crayfish Constant (CC):

Where: W – total weight, TBL – total length, CPL – carapace length, CPW – carapace width (Streissl, Höld, 2002)

For the determination of the mass, we used a balance of type "Kern" (Kern PFB Version 2.2) max. weighing 1200 g with an accuracy of 0.01 g, and morphometric measurements were taken using a caliper gauge (made by Stainless Hardened) with an accuracy of 0.02 mm. Measured values of morphometric characters were processed statistically (minimum, maximum, mean values, standard deviation and coefficient of variation) using the Microsoft Office Excel 2007 statistical program, interpreted and compared with available literature data.

 

Results

Of the 35 analyzed specimens, 22 (i.e. 62.86%) were males and 13 (37.14%) females (sex ratio 1.69:1).

 


Figure 1: Pontastacus leptodactylus - Danube crayfish (male left, female right).

 

The results of the measurement of morphometric parameters in Danube crayfish specimens from the lower Vrbas River are presented in the table as the mean value, minimum (min), maximum (max), standard deviation (SD) and coefficient of variation (CV). The results are shown together for all specimens, as well as separately for males and females.

The values obtained for all of the analyzed specimens show that the average body weight is 27.28 g, the average length of the body is 98.86 mm, the length of the claw is 36.54 mm, the length of the cephalothorax is 49.66 mm, the width of the carapace is 27.98 mm, the length of the abdomen is 35.91 mm, the length of the rostrum is 16.88 mm, and rostrum width is 7.27 mm. Based on these values, the standard deviation (SD) has the highest value for body length (16.79), body weight (11.75) and length of cephalothorax (11.01), slightly lower for the length of the claw (9.07), the length of the abdomen (8.92), carapace width (4.71), even less for the length of the rostrum length (3.81), while the smallest for the width of the rostrum (1.86). Two morphometric characters fall into a low variable (CV 10 - 20%), which are: (TBL and CPW). It belongs (CLL, CEF, ABL, ROL, ROW) in moderately variable (CV 20 - 30%), while only one morphometric characteristic W (CV = 43.05%) show high variability (CV > 30%) (Table 1).

 

Table 1: Descriptive statistics - mean value, standard deviation, ranges of measured morphometric characteristics for all specimens of species P. leptodactylus from the Vrbas River.

 

The obtained values for males show that the average body weight is 30.82 g, the average length of the body is 103.91 mm, the length of the claw is 39.65 mm, the cephalothorax length is 53.4 mm, the width of the carapace is 27.72 mm, the length of the abdomen is 39.94 mm, the length of the rostrum is 17.67 mm and the rostrum width is 7.53 mm. On the basis of these values, the standard deviation (SD) was obtained which had the highest value for the body length (11.59), slightly less for the mass (11.95), the length of the cephalothorax (8.49), the length of the claw (8.39), the length of the abdomen (8.18) the width of the carapace (4.56), while it is least for the length (3.6) and the width (2.13) of the rostrum. According to the analysis of morphometric characteristics, low variable characters (CV 10 - 20%) are defined, which are: (TBL, CEF, CPW). In males (whose coefficient of variation CV 20 - 30%), moderately variable characteristics are CLL, ABL, ROL, ROW. The highly variable characteristic (CV > 30%) is only the mass, W (38.87) (Table 2).

 

Table 2: Descriptive statistics - mean value, standard deviation, ranges of measured morphometric characteristics for males of species P. leptodactylus from the Vrbas River.

 

The obtained values for females show that the average body weight is 20.8 g, the average length of the body is 89.61 mm, the length of the claw 30.32 mm, the length of the cephalothorax 42.18 mm, the width of the carapace 27.85 mm, the length of the abdomen 28.19 mm, the length of the rostrum 14.69 mm and the width of rostrum 6.83 mm. Based on these values, the standard deviation (SD) has the highest value for the length of the body (14.73), slightly less for the length of the cephalothorax (12.01), the weight of the body (8.31), the length of the claw (7.23), the carapace width (5.21), the length of the abdomen (4.52), while it is the least for the length (3.12) and the width (1.24) of the rostrum. The four observed morphometric characteristics are of low variables (CV 10 - 20%), the three observed morphometric characteristics are moderately variable (CV 10 -20% Table 3), while the only one morphometric characteristic W (CV = 39.93%) is highly variable CV > 30%) (Table 3).

 

Table 3: Descriptive statistics - mean value, standard deviation, ranges of measured morphometric characteristics for females of species P. leptodactylus from the Vrbas River.

 

Males and females are statistically significantly different (p < 0.0001) in five morphometric characters. These are: W (p = 0.007), TBL (p = 0.008), CLL (p = 0.002), CEF (p = 0.002), ABL (p = 0.0001) and ROL (p = 0.006) (Table 4). There was no statistically significant difference (p > 0.05) for CPW (p = 0.456) and ROW (p = 0.075) (Table 4). By comparing the mean values of the width of the carapace and the width of the rostrum among the sexes, the Danubian crayfish males have a higher mean value for the previously mentioned morphometric characteristics compared to females, but that the difference is not statistically significant.

 

Table 4. Significance of differences between mean values of morphometric characteristics of crustaceans species P. leptodactylus from the Vrbas River.

 

During the statistical data processing, the correlation between total body length and male weight (r = 0.77) and females (r = 0.90) was determined (Figure 2). It means that body weight increases as the body length increases.

 

Figure 2: The ratio of body length and body weight of males (left) and females (right) of Danube crayfish.

 

The correlation between body weight and the length of the claw in both males and females was made, and we see that there is a positive correlation, which means that the growth of the claw accompanies the body weight. The correlation coefficient in males is r = 0.77, and in females is r = 0.93 (Figure 3).

 

Figure 3: Relation of body weight and claw length in males (left) and females (right) of Danube crayfish.

 

Based on the coefficient of correlation by applying regression analysis, it is seen that the coefficient is highly statistically significant between the width of the carapace and the length of the body. The correlation coefficient in males is r = 0.80, and in females r = 0.94 (Figure 4).

 

Figure 4: The ratio of body length and width of a carapace in males (left) and females (right) of Danube crayfish.

 

The least CC is 0.123 (for females) and the highest 0.582 (in males). The mean value for females is 0.234 and for males 0.373. The least FCF is 0.014 (female), and the largest is 0.059 (in males). The mean value for males is 0.038 and for females 0.028 (Table 5).

 

Table 5. Values for condition factor for Danube crayfish specimens.


Discussion

The overall sex ratio is balanced if the ratio of males and females is approximately 1 : 1 (Lewis, 2002). In the research conducted in 2018 and 2019 in the Vrbas River, the sex ratio was 1.69 : 1 (males : females), and a more significant proportion of males in the sample could be attributed to the fact that during the field survey, five females with pleopod eggs, were sampled, indicating that obviously there was still a season of less activity in females (the period of wearing eggs lasts from November to June of the following year) (Köksal, 1988). The insight into the sex ratio in the population is of great importance because the uniform sex relationship is the sign of a healthy and stable population (Jurković, 2016).

The population of Danube crayfish of the species P. leptodactylus in the explored locality has a relatively stable age structure. At the explored location on the Vrbas River, the largest group was 81 - 100 mm with 47.06%. The longest male had 135.36 mm, and the longest female was 112.73 mm, which corresponds to the range of 38 - 143 mm for females and 33 - 156 mm for males listed in the literature (Deniz et al., 2010), as well as with values which were recorded by Çevik (1993), Güner (2000) and Erdem et al. (2001) The heaviest male weighed 45.32 g, while the heaviest female was 27.9 g. A higher average weight of males can be attributed to the fact that males have a more massive claw that contributes to their higher body weight compared to females (Jurkovic, 2016).

Morphometric characteristics of males and females P. leptodactylus from the Vrbas River statistically significantly differ (p < 0.05), with higher mean values being established for most of the male characteristics (Table 4). The results obtained can be related to the pronounced sexual dimorphism of crustaceans of this type, whereby males are larger than females (Vasileva et al., 2017).

According to the values of the calculated indices, it is evident that males are in better condition than females. Similar data on the values of the conditional factor is provided by studies conducted on adult males and females related species Astacus astacus (Trožić-Borovac et al., 2012). Streissl and Hödl (2002) disclose the correlation between the condition of crustaceans bodies and habitat characteristics. Namely, the research found that a greater diversity of streaming and a greater diversity of the substrate composition of the bottom has a positive effect on the condition of the body of the crustaceans. These allegations are in line with our results if we take into account the characteristics of the explored site.

 

Conclusion

Morphometric characteristics of crayfish were observed (Pontastacus leptodactylus) from the lower Vrbas River stream downstream from Razboj.

Eight morphometric characters and two condition factors were analyzed on all 35 specimens (22 males and 13 females).

The obtained values of the morphometric characters of stream crayfish in the areas of Razboj partially fit into a known range of variability and represent the first data for the given area.

The existence of statistically significant differences among adult sizes in the body mass, the total length of the body, length of the claw, length of the cephalothorax, length of the abdomen and length of the rostrum in male compared to females is confirmed, which is explained by the sexual dimorphism of crustaceans.

The data presented in this paper can serve as a basis for further research of the species P. leptodactylus in this area.

 

Acknowledgments

The paper presents the result achieved by realization of Program for the conservation and sustainable use of genetic resources of Republic of Srpska, financed by the Ministry of Scientific and Technological development, Higher Education and Information Society performs of the Republic of Srpska and implemented by the Institute of Genetic Resources of the University of Banja Luka.

Expert opinion on the research of biodiversity was issued by the Republic Institute for the Protection of Cultural, Historical and Natural Heritage (No. 30 / 625-723 / 18, 09.10. 2018th year; number 07/1.30/625-020/19, dated 23.1. 2019).


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