Effect of feeding under-year zander (Sander lucioperca) on size, body mass and body composition before and after wintering

Zander (Sander lucioperca) is one of the most important fish species in the German inland fishery. As a pelagic predator, zander is able to regulate populations of small cyprinids and perch and is therefore used in ‘top‐down’ projects to directly control the food web. At present, natural waters are mainly stocked with one‐summer‐old zander from pond hatcheries; however, such fish are poor stocking material due to low survival rates, presumably because of their small size. Two groups of 50‐day‐old zander fingerlings reared in a recirculation system (T = 23 °C) were used. For 90 days one group (FG 1) was fed with a commercial dry feed (Trouvit Pro Aqua Brut), and the other group (FG 2) was fed with chironomides (Chironomus spp.). The fat content of the dry feed was increased with fish oil supplemented up to 22%. After the rearing period the FG 1 fishes attained the largest size and fat content. A pond with a surface of 667 m² and a mean depth of 0.8 m was stocked with 24‐tagged zander (12 of each feeding group) for wintering. After the winter period of 176 days, survival rate of each feeding group was 83.3%. The fatty acid composition in the membrane lipids of group 2 changed dramatically. In contrast to previous investigations, presented results indicate that the survival rate is not influenced by fish size (weight and length). The crucial factors for high survival rates of zander during wintering are the crude tissue fat content (>5%) and its fatty acid composition.