Biology and distribution of Danube barbel (Barbus balcanicus) (Osteichthyes: Cyprinidae) at the Northwestern limit of its range

Abstract

Presence of Danube barbel Barbus balcanicus was investigated at the westernmost portion of its distribution area (Italian portion of the Isonzo River Basin). Genetic analyses carried out on specimens collected in different watercourses confirmed B. balcanicus presence in the same locations where Barbus caninus was erroneously classified in the past. More precisely, 4 Cyt b haplotypes belonging to the Balkanic species were described, three of which were evidenced for the first time. Analysis of meristic characters also confirmed genetic results and completed the taxonomical assessment. At the same time, a target population was studied to deepen knowledge about the species ecology. In this case, 120 specimens belonging to five age classes (from 0+ to 4+) were collected with monthly frequency in Barbucina Creek, representing the model watercourse inhabited by the species in the study area. Regression between total weight (W) and standard length (S L ) did not differ significantly between males and females, therefore not displaying sexual dimorphism. S L values showed wide ranges, often overlapping among age classes. Mean condition factor (Kmean) decreased significantly with growth and age, as small individuals were in better nutritional condition. From an ecological point of view, biometric parameters seemed to be affected by habitat conditions and, specifically, to the limited space of the creeks, rather than by trophic conditions. Finally, trends of gonadosomatic index (GSI) showed that B. balcanicus reproductive period stretches between April and late May/early June. Results indicated that sexual maturity is reached at 1+ age, corresponding to a mean standard length equal to 5.50 ± 0.66 for female and 5.71 ± 0.53 for male breeders. In conclusion, experimental results highlighted the presence and adaptability of this "forgotten" species of the Italian fish fauna, which certainly will deserve attention in a future amendment of the Italian IUCN Red List of vertebrates.

First look into the evolutionary history, phylogeographic and population genetic structure of the Danube barbel in Croatia

“…The Danube barbel is a small rheophilic, lithophilic and benthopelagic freshwater fish that dwells in fast and moderately fast streams with a gravel bottom, mostly residing in riffles and waterfalls. Its distribution area, besides Croatia, includes Bosnia and Herzegovina, Serbia, Macedonia, Southwestern part of Romania, Bulgaria, watercourses of Aegean basin and Isonzo (Soča) River basin (Kottelat & Freyhof, 2007;Buonerba et al, 2015;Bertoli et al, 2019). During the spawning season (May to July), the Danube barbels migrate upstream in search of highly oxygenated currents to spawn (Kottelat & Freyhof, 2007;Žutinić et al, 2014).…”

“…Barbels have been the focus of many molecular studies investigating the relationships between species and populations in specific European regions (Tsigenopoulos and Berrebi, 2000). Such studies including Barbus balcanicus have been carried out in Italy (Meraner et al, 2013;Buonerba et al, 2015;Bertoli et al, 2019) Serbia (Simonović et al, 2018), Albania (Marková et al, 2010) and Macedonia (Velkova-Jordanoska et al, 2013), but to date not in Croatia.…”

“…Barbus balcanicus primarily colonizes the small tributaries of the Isonzo (Soča) River system near the border with Slovenia, though its distribution in Italy could be wider since it was often erroneously classified as B. caninus given the high morphological similarity. However, Bertoli et al (2019) stated that ecological preferences of these two species differ, as B. caninus requires oxygenated waters and high current speed while B. balcanicus prefers lower flow rates, cobble/flat rock substrates and less cover vegetation. Populations of B. balcanicus have been found in sympatry with B. plebejus (Pneuma Creek, Piumizza and Reca Streams), indicating possible hybridization (Bertoli et al, 2019).…”

“…However, Bertoli et al (2019) stated that ecological preferences of these two species differ, as B. caninus requires oxygenated waters and high current speed while B. balcanicus prefers lower flow rates, cobble/flat rock substrates and less cover vegetation. Populations of B. balcanicus have been found in sympatry with B. plebejus (Pneuma Creek, Piumizza and Reca Streams), indicating possible hybridization (Bertoli et al, 2019).…”

“…Cyt b is frequently used for describing the structure and origin of fish populations (e.g. Perea et al, 2010;Buj et al, 2014Buj et al, , 2019Buj et al, , 2020Schenekar et al, 2014), including molecular studies of the genus Barbus (Tsigenopoulos and Berrebi, 2000;Kotlík et al, 2002;Bertoli et al, 2019;Zaccara et al, 2019).…”