Suitability of Different Food Types for On-Feeding and Juvenile Production of European Grayling, Thymallus thymallus, under Intensive Farming Conditions

In the present study on-feeding and juvenile production of European grayling, Thymallus thymallus, was tested with a commercially available fry food for salmonids (FSS) and a specific self-made fry food containing zooplankton components (DFZO) under intensive farming conditions. Live zooplankton food was used as control. Rearing of grayling was not possible with FSS as in > 70% of the fish malformations manifested circa 30 days after on-feeding. Malformed fish had sharply bent tails and gas accumulations in the coelomic cavity and intestine. These alterations were reversible and compensated when fish were fed on a live zooplankton diet instead of FSS for 2 weeks. When grayling were fed with DFZO during the first 14 days and with FSS thereafter, survival rates 49 d after first feeding were 85 ± 3%, increase in total length was from 15.7 ± 0.9 mm (day of first feeding) to 27.1 ± 1.2 mm (day 49) and in weight from 20 ± 2 mg to 110 ± 13 mg. The percentage of malformed fish was < 0.5%. These viability parameters did not significantly differ from fish fed with live zooplankton food.