Abstract: The subject of the study was vendace Coregonus albula L. This species is a typical planktivore and inhabits the pelagic zone of Lake Pluszne (area - 903 ha, 51 m - maximum depth) located in northeastern Poland. Acoustic measurements were taken with a Simrad EY500 type split beam echosounder at a frequency of 120 kHz, with beam divergence of 7x7 degrees and a pulse duration of 0.3 ms. The data were analyzed using the trace tracking method with the EP 500 program and 5696 fish traces. A total of 3092 vendace individuals were caught in various water layers with a pelagic trawl during control fishing. The study involved determining the dependence between the acoustic size of vendace TS in dB, body length L in cm and specimen weight. The measurements were carried out in June and October 2003 under varied environmental conditions that limited spatial distribution, density and the condition of the examined fish. The dependencies of TS (dB) on fish body length L (cm) were determined for the average values of TS_S.A. = 20 log L –65.4 ± 0.1 SE and TS_max = 20 log L – 63.8 ± 0.1 SE.