A high level of freshwater fish endemism in the Balkans Region emphasizes the need for non-native species risk assessments to inform management and control measures, with pre-screening tools, such as the Fish Invasiveness Screening Kit (FISK) providing a useful first step. Applied to 43 non-native and translocated freshwater fishes in four Balkan countries, FISK reliably discriminated between invasive and non-invasive species, with a calibration threshold value of 9.5 distinguishing between species of medium and high risk sensu lato of becoming invasive. Twelve of the 43 species were assessed by scientists from two or more Balkan countries, and the remaining 31 species by a single assessor. Using the 9.5 threshold, three species were classed as low risk, 10 as medium risk, and 30 as high risk, with the latter category comprised of 26 moderately high risk, three high risk, and one very high risk species. Confidence levels in the assessments were relatively constant for all species, indicating concordance amongst assessors.

Mitochondrial DNA (mtDNA) haplotypes of brown trout (Salmo trutta L.) populations in the area of Djerdap National Park were analyzed in order to determine their phylogeographic statuses. Sequencing the control region of mtDNA in 66 specimens from 9 streams in the broader Iron Gate area revealed that 7 brown trout from those streams carried haplotypes of Atlantic lineage, while the remaining 59 fish were of Danubian lineage, either of Da23c or Da1 haplotypes. Four streams were inhabited by populations of the indigenous Da23c mtDNA haplotype, while the population in one stream had the Da1 haplotype. In the remaining 4 streams, brown trout of exclusively Atlantic lineage were present in 3, while those of the Da23c haplotype were additionally present in the fourth. The significant fixation index Fst in all populations, caused by a significantly large proportion of the among-population component of variance, revealed the fixation of particular haplotypes in the majority of populations. The size of a particular stream determines native brown trout abundance and limits their suitability for restorative purposes.

Modern fly fishing, mainly for brown trout and grayling, has been done on a local scale and in low extensity in Serbia for over 50 years. Data obtained from 117 fly fishermen filling out an online questionnaire, with 30 questions processed using multivariate analysis, revealed that most fishermen who had started fly fishing since 2000 were under 40. Only few who were under 20 started to fish initially with the fly fishing equipment. They turned up committed to and skilled in fly fishing. Most of them live in large municipalities with much better economic opportunities. Their level of education is above average in Serbia. Economic power, place of residence and level of education outline their fishing capabilities, frequency of fishing outings, distance they travel to fly fish, as well as their attitudes towards fishery policy, conservation of native brown trout and grayling stocks, management of streams and communication with other fly fishermen.

The Chinese mitten crab Eriocheir sinensis is listed in The Global Invasive Species Database and the IUCN Register as one of “100 of the world’s worst invasive alien species”. It has been reported in Serbia since 1995 in the Danube River, suggesting a predominantly human-aided dispersal. The risk of invasiveness posed by the Chinese mitten crab to aquatic ecosystems in Serbia, assessed using the FI-ISK (Freshwater Invertebrate Invasiveness Scoring Kit, v1.19), revealed a final score of 37. This shows a high potential of invasiveness, mainly due to its versatile ecological and biological features in a climate similar to that in the donor area. FI-ISK assessment revealed the alleged environmental impact of Chinese mitten crab in Serbia to be of much greater impact on aquaculture than previously assumed