Stress and survival of small pike-perch Sander lucioperca (L.) after trawling and chilling

The mortality and stress responses (plasma cortisol concentration) of undersized (total length, L-T, <370 mm) pike-perch Sander lucioperca caught as by-catch in a trawl fishery were assessed. The effects of three different holding methods on pike-perch caught by trawl were compared: (1) fish that were transferred to ambient-temperature water (15.0-21.4 degrees C) immediately after capture and not exposed to chilling water, (2) fish held in chilling water for 10 min and (3) fish exposed to chilling water for 2 h. The sample fish were held and monitored in individual plastic restrainers at ambient-water temperature for 48 It after each of the handling procedures. Total mortality was similar for fish held in chilling tanks for 10 min (27.2% total mortality) compared to fish that were only held in ambient-temperature water (28.2% mortality). Total mortality reached 91.3% when fish were held in chilled water for 2 h. Mortality and plasma cortisol concentrations correlated inversely with size (96-368 mm L-T) and directly with lake-water temperature (15.0-21.4 degrees C) after treatment. In addition, the effect of chilling was observed in elevated cortisol concentration and delayed start of recovery. The results show that quickly removing (<10 min) undersized pike-perch from chilled water could markedly improve the survival of released fish. Due to delayed recovery, however, fish should be allowed to recover (30-40 min) in a deck tank before release. (C) 2008 The Authors. Journal compilation (C) 2008 The Fisheries Society of the British Isles.