The life‐history traits and population dynamics of the black bullhead Ameiurus melas (Rafinesque) were studied monthly from August 2009 to December 2012 in Lake Sava in Belgrade (Serbia). This period included a mass mortality event in May 2011 and subsequent population recovery during 2012. Available evidence suggests the mass mortality was caused by European catfish virus that only affected the black bullhead. Changes in key life‐history traits and the recovery potential (increase in catch‐per‐unit‐effort, doubling of young‐of‐the‐year to adult ratio, earlier maturation and increased fecundity) following the mass mortality event suggest population resilience typical of a recurring boom‐bust pattern and demonstrate the species’ capacity to recover rapidly and re‐establish following disturbance. Repeated systematic mass removals of both juveniles and adults (using fyke nets) will be required if future fishery management measures aimed at limiting the population size are to be effective.

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The black bullhead is an invasive species that forms dense populations and has a negative impact on the native ichthyofauna. Recent studies indicate that it is one of the most dominant invasive fish species in Serbian waters. Feeding habits based on stomach contents of individuals caught in Lake Sava were analyzed as a first step towards evaluating its possible negative impact on the native fish fauna of the lake. The following indices for diet analysis were applied: vacuity index, frequency of occurrence, numerical abundance and prominence value. Trophic niche breadth and seasonal trophic diversity were calculated using the Shannon?s index. The diet spectrum comprised 16 different prey categories from five groups: Mollusca, Crustacea, Insecta, Teleostei and plants. Fish were the main prey in all seasons, followed by aquatic invertebrates. Plant material and terrestrial insects were used as food in relatively small quantities. Predation on fish eggs was also detected. Our research confirmed that this species is an opportunistic generalist. An ontogenetic diet shift was also detected. The lowest value of trophic diversity was found in age 1+ individuals (H=1.39), while the highest was found in age 3+ individuals (H=2.00). The widest niche breadth was recorded in spring 2011 (H=2.12).

In recent decades, the Amur sleeper (Perccottus glenii) is one of the most impressive east-to-west invaders of European inland waters, but there are insufficient data on its biology in the countries it has entered. Specimens of two sets of samples from November 2015 (n=25) and October 2016 (n=39) were caught in the Danube River channel near Veliko Gradiste (Serbia) by electrofishing. Thirty morphometric and eight meristic characteristics of the collected fish were measured with the aim of describing the general body shape in more detail using the ?point-to-point? method. This is the first attempt to obtain morphometric and meristic characteristics of Amur sleeper caught in Serbia. The results revealed a relatively low variability in the morphometric and meristic characters of the studied population. When compared to other studies, there was a great variability of the studied characteristics between geographically distant European populations that inhabit different water body types. Female fish had more robust bodies compared to males of the same length, while males had longer pectoral, anal and dorsal fins. Additionally, 2+ individuals had more robust heads and jaws, as well as longer anterior parts of the body compared to 1+ individuals of the same size

Black bullhead is among the most abundant and successful non‐native fish species in European fresh waters. A number of studies have indicated that its physical removal might be a potential solution to minimize possible adverse impacts; however, so far there have been no field studies to confirm this. This study quantified the population dynamics of both native and non‐native fishes in a small slow‐running lowland river within the Ponjavica Nature Park in Serbia before and after the black bullhead removal with fyke nets. The removal of black bullhead resulted in statistically significant changes in the abundance of two native species – an increase in rudd (Scardinius erythrophthalmus) (by 5.3 times) and a decline in bleak (Alburnus alburnus) (by 2.3 times). A significant increase was observed in three non‐native fish species – the abundances of topmouth gudgeon (Pseudorasbora parva), pumpkinseed (Lepomis gibbosus) and Prussian carp (Carassius gibelio) increased 25.5, 4.9 and 4.2 times, respectively. There were also substantial changes in the diversity of the fish assemblage after the black bullhead removal, illustrated by changes in diversity indices: Shannon's index doubled, while the Simpson's dominance index decreased threefold. The catch‐per‐unit‐effort and the biomass‐per‐unit‐effort values indicated the dominance of the black bullhead in the fish assemblage during the mass removal phase of the study. The young‐of‐the‐year/adult ratio did not vary in relation to abundance, which confirmed that black bullhead might not compensate for fishing mortality with increased recruitment. The results suggest that black bullhead plays a significant role in structuring the fish assemblage and that its removal may have both positive and negative effects on species abundance and diversity. These findings can contribute to the conservation of native fish species and improvement of future management programmes.