Utilization of treated sewage grown zooplankton in whitefish Coregonus lavaretus [L.] fry rearing

The reintroduction of whitefish to Puck Bay generates a great demand for its autumn fry. This results in attempts to find new solutions that would enhance local stocking potential. One of such solutions is to use the zooplankton grown in treated wastewater as the food for whitefish fry. This report presents the variability of zooplankton species composition and biomass growing in the effluent of the sewage treatment plant located in Swarzewo, Poland. Filtered zooplankton was used to feed whitefish fry reared in a seawater-filled pond during May to September, 2003. Food analysis of the fry has demonstrated that the zooplankton was highly preferred as food, both in terms of quality and quantity. Daphnia longispina was the dominant food item over the entire period; however, in September Neomysis integer played a similar role. The weight of the supplied zooplankton outweighed the daily requirement of the fry many fold during May-June, providing enough food for the current stocking density over the remaining months. At the end of September, the juveniles with a mean length of 128.4 mm and a body weight of 20.6 g were released to Puck Bay.