Vera Nikolić

Huchen or Danube salmon Hucho hucho (Linnaeus 1758) is one of the largest salmonid species in the world and the largest species native to the Danube basin in Europe. In Serbia, this species inhabits the Drina river system, as well as the upper reaches of the River Ibar. It has already been introduced into the rivers Moravica and Đetinja, which are part of the Zapadna Morava catchment area. Most recently, huchen was stocked from its native habitat into the rivers Jerma and Nišava in the Južna Morava river system, and into the River Mlava which flows into the Danube. Huchen is listed as an endangered (EN) species on the IUCN Red List of Threatened Species and is protected in Serbia, and a Conservation Action Plan has already been adopted. In this report, we present the first record of this species in the River Grza, which is a part of the Velika Morava river system, outside its native range. The ichthyofauna of this recipient river consists of brown trout Salmo trutta L. and Eurasian minnow Phoxinus phoxinus L. In a small river of a fragile ecosystem such as this, the introduction of huchen as an apex predator can seriously harm the species of the native fish community, which warns of the illegal stocking measures currently in process.

On the survey of the recent records, the fish and lamprey fauna of the River Sava catchment consists of 74 species, 15 of which being considered alien. The indigenous species diversity, explained using the relation N = 0. 546 A 0.232, fits well into the range common for large catchments in Europe. Both taxonomic and ecological diversity, as well as the character of fish communities in streams and rivers, are strongly correlated with the stream order. On the relative abundance of species in fish communities, the upper rhithron fish communities cluster distinctly from those belonging to the middle rhithron, within which several subgroups of fish communities were distinguishable. Fish communities of the middle rhithron character in streams and small rivers stand distinctly apart from those belonging to particular sections of large rivers (e.g., the Rivers Sava, Drina, Vrbas, and Bosna), with the transitional type of middle rhithron fish community in larger rivers (e.g., those in the Rivers Una and Sana) that resemble more to the fish communities common in middle rhithron streams. Fish communities in the middle section of the River Sava in Croatia and in the bordering area with Bosnia and Herzegovina mainly belong to the lower rhithron, attaining the character of potamon in the most downstream, Serbian section. River Sava’s fish communities strongly interact with the ones occurring in the most downstream sections of their largest tributaries, e.g., the Rivers Una, Vrbas, Bosna, Drina, and Kolubara, which makes them very similar in structure in the areas of river mouths. Classification of fish communities based solely on the presence and absence of species revealed similar general pattern of fish community classification, though with the more sharp delimitation between those belonging to the upper and middle rhithron on one and to the lower rhithron and potamon on the other side. That was supported by the determination of fish communities belonging to the upper rhithron with brown trout Salmo cf. trutta, European bullhead Cottus gobio, and minnow Phoxinus phoxinus as the most common fish species. Fish communities belonging to the middle rhithron were determined mainly with chub Squalius cephalus and spirlin Alburnoides bipunctatus, whereas brook barbel Barbus balcanicus and stone loach Barbatula barbatula occurred in both upper rhithron and middle rhithron. Nase Chondrostoma nasus were associated with both middle and lower rhithron fish communities. The most common fish species that determine the lower rhithron fish communities were common bream Abramis brama, ide Idus idus, and bleak Alburnus alburnus, with the northern pike Esox lucius, Balon’s ruffe Gymnocephalus baloni, and racer goby Neogobius gymnotrachelus as significant species explaining fish communities of both lower rhithron and potamon. The level of production of fish in the River Sava varies remarkably within the sections with the similar ecological features, as well as between the sections that differ for the type of fish community. The greatest biomass and annual natural production were recorded in the sections homing the potamon and lower rhithron fish communities, especially in the flooding areas of side arms and oxbows which serve as spawning areas and nurseries. A total of 15 alien fish species was recorded in the River Sava catchment, the Prussian carp Carassius gibelio and brown bullhead Ameiurus nebulosus being assessed the most invasive in the areas with the potamon fish community. A strong impact from both long-term and recent stocking with alien hatchery-reared brown trout strains and rainbow trout in the upper rhithron fish communities was recently recognized. Mudminnow Umbra krameri and huchen (or Danube salmon) Hucho hucho are considered the two most threatened fish species of the River Sava catchment, where various types of riverbed modifications, especially the damming, were seen the most prominent threatening factors for fish diversity.

The collaboration in recent projects in the Black Sea basin of the continental Croatia and Serbia revealed novelties regarding the molecular diversity in indigenous brown trout Salmo trutta. The contemporary conservational state-of-art and traditional brown trout fisheries’ management approach are strongly opposed. Mapping of diversity revealed also history of impact from fishery management by stocking.

Data about the mitochondrial DNA haplotypes of brown trout (Salmo trutta L.) in the area of the Danube River Basin in Bosnia and Herzegovina have not been hitherto published. Brown trout from the drainage area of the Una River was assessed for the first time using the Control Region of the mitochondrial DNA. Anal fin clips of 43 brown trout specimens were sampled from four sites in the headwater section and in two tributaries joining the Una River in the middle section. In total, three CR haplotypes were recorded: Da2 and Da22 from the Danubian and At1 from the Atlantic brown trout lineage. Da22 haplotype was inferred the native one in the Una River drainage area owing to its most frequent and most upstream dispersal in the headwater section. The other two haplotypes were found with the native one only in one or two tributaries joining the Una River in the middle section. They are considered alien and were most likely introduced by stocking with hatchery reared brown trout fingerlin...

On the survey of the recent records, the fish and lamprey fauna of the River Sava catchment consists of 74 species, 15 of which being considered alien. The indigenous species diversity, explained using the relation N = 0. 546 A0.232, fits well into the range common for large catchments in the Europe. Both taxonomic and ecological diversity, as well as the character of fish communities in streams and rivers are strongly correlated with the stream order. On the relative abundance of species in fish communities, the upper rithron fish communities cluster distinctly from those belonging to the middle rithron, within which several sub-groups of fish communities were distinguishable. Streams and small rivers of fish communities of the middle rithron character stand distinctly apart from those belonging to particular sections of large rivers (e.g., the Rivers Sava, Drina, Vrbas and Bosna), with the transitional type of middle rithron fish community in larger rivers (e.g., those in the Rivers Una and Sana) that resemble more to the fish communities common for middle rithron streams. Fish communities in the middle section of the River Sava in Croatia and in the bordering area with the Bosnia and Herzegovina mainly belong to the lower rithron, attaining the character of potamon in the most downstream, Serbian section. River Sava’s fish communities strongly interact with the ones occurring in the most downstream sections of their largest tributaries, e.g., the Rivers Una, Vrbas, Bosna, Drina and Kolubara, which makes them very similar in structure in the areas of river mouths. Classification of fish communities based solely on the presence and absence of species revealed similar general pat-tern of fish communities classification, though with the more sharp delimitation between those belonging to the upper and middle rithron on one, and to the lower rithron and potamon on the other side. That was supported by determination of fish communities belonging to the upper rithron with brown trout Salmo cf. trutta, European bullhead Cottus gobio and minnow Phoxinus phoxinus as the most common fish species. Fish communities belonging to the middle rithron were de-termined mainly with chub Squalius cephalus and spirlin Alburnoides bipunctatus, whereas brook barbel Barbus balcanicus and stone loach Barbatula barbatula occurred in both upper and middle rithron. Nase Chondrostoma nasus were associated with both middle and lower rithron fish communities. The most common fish species that determine the lower rithron fish communities were common bream Abramis brama, ide Idus idus and bleak Alburnus alburnus, with the northern pike Esox lucius, Balon’s ruffe Gymnocephalus baloni and racer goby Neogobius gymnotrachelus as significant species explaining fish communities of both lower rithron and potamon. The level of production of fish in the River Sava varies remarkably within the sections with the similar ecological features, as well as between the sections that differ for the type of fish community. The greatest biomass and annual natural production were recorded in the sections homing the potamon and lower rithron fish communities, especially in the flooding areas of side arms and oxbows which serve as spawning areas and nurseries. A total of 15 alien fish species was recorded in the River Sava catchment, the Prussian carp Carassius gibelio and brown bullhead Ameiurus nebulosus being assessed the most invasive in the areas with the potamon fish community. A strong impact from the both long-term and recent stocking with alien hatchery reared brown trout strains and rainbow trout in upper rithron fish communities was recently recognized. Mudminnow Umbra krameri and huchen (or Danube salmon) Hucho hucho are considered the two most threatened fish species of the River Sava catchment, where various types of river bed modifications, especially the damming, were seen the most prominent threatening factors for fish diversity.

Native Brown Trout Salmo trutta reveal remarkable diversity in Serbia, with eight exclusive and a couple of more widely spread mtDNA haplotypes. Insufficiently controlled stocking is a main threat to that, as well as to the amenity value of wild Brown Trout. Native or wild Brown Trout stocks deteriorated as a consequence of stocking with inappropriate strains. Three nonnative trout species and three Brown Trout strains stocked into streams of Serbia were classified as medium-high to high risk of being invasive. Alien Brown Trout strains crossbreed with, and incorporate into the native Brown Trout stocks. Fly fishermen in Serbia greatly differ in attitudes towards fishery policy, management, and conservation of native Brown Trout stocks. They are opposed to conservation measures that may affect angling quality. Though declaratively being conservation-friendly, the majority of anglers consider stocking more efficient than Catch-and-Release (C&R) regulations. Despite good conservational and fishery effects of C&R, increases in license sales from fishermen presses trout farmers and fishery managers to stock, regardless of adverse effects on native Brown Trout stocks. Subsidiaries to farmers and grants awarded to fishery managers could promote stocking of native strains and conservation of native stocks.

Native brown trout Salmo cf. trutta reveal remarkable diversity in Serbia, with eight exclusive and a couple of more widely spread mtDNA haplotypes. Insufficiently controlled stocking is a main threat to that, as well as to the amenity value of wild brown trout. Native or wild brown trout stocks deteriorated as a consequence of stocking with inappropriate stocking material. Three of non-native trout species and three brown trout strains stocked into streams of Serbia were classified as medium-high to high risk of being invasive. Alien brown trout strains cross breed with, and incorporate into the native brown trout stocks. Fly fishermen in Serbia greatly differ in attitudes towards fishery policy, management and conservation of native brown trout stocks. They are opposed in tolerance toward the impact of conservational demands on the quality of fishing. Though declaratively being conservation-friendly, majority acts as considering stocking more efficient than Catch-and-Release (C&R). Despite a good conservational and fishery effects of C&R, increase in incomes from fishermen presses trout farmers and fishery managers to stock, regardless of adverse effects on native brown trout stocks. Subsidiaries to farmers and grants awarded to fishery managers could promote use of native stocking material and conservation of native stocks