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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

Three localities, representing three distinct coastal areas, were investigated: 1. the mouth of the Sutorina River; 2. the mouth of the Jaska River; 3. the mouth of the Bojana River (right branch). Regarding the composition of young mullet assemblages, Lisa saliens, Lisa ramada and Lisa aurata were dominant at the first locality; L. aurata and Chelon labrosus at the second; and at the third L. ramada was clearly dominant, Mugil cephalus occupied the subdominant position, while L. aurata was absent. The seasons of the first appearance of migratory fry were October, April, November, October and July, for M. cephalus, C. labrosus, L. ramada, L. aurata and L. saliens, respectively. Migratory periods varied from 2 (C. labrosus) to 7 (L. ramada) months.

In spectral sensitivity studies, electroretinograms (ERG) were recorded from the in situ eyecup of immobilized perch (Perca fluviatilis) electrofished in the floodplain zone of the Danube River. It is shown that the ERG b-wave is a good indicator of spectral sensitivity, although it reflects the activity of photoreceptors indirectly. With a maximum around 542 mm, the scotopic spectral sensitivity of perch obtained using fitted amplitude-log intensity functions for threshold calculation and two models developed in our laboratory for computer-assisted fitting of spectral sensitivity curves did not differ from the sensitivity determined using the microspectrophotometric and isolated pigment methods (maximum around 541 nm).