TANK-CAGE METHOD OF REARING COREGONID (COREGONIDAE) FISH. II. EUTROPHIC LAKE
Jacek Kozłowski, Paweł Poczyczyński, Dariusz Dostatni, Andrzej Mamcarz
Department of Fisheries, Warmia and Masuria University in Olsztyn
ABSTRACT. The aim of the studies was to determine the possibility of using a combined rearing system of tanks and illuminated cages for coregonid larvae in eutrophic lake. Studies were carried out in 1990. Tank rearing took place in Dgal Hatchery, cage rearing was performed in eutrophic Lake Leginskie.
Increasing the egg incubation temperature, larvae hatching was accelerated about 3 weeks earlier. The larvae were reared on artificial feeds, at 16 ±1 EC, for a period of 19 days. Then they were transferred to illuminated cages, in which they fed on the zooplankton only. The control group consisted of the larvae hatched in the usual period in cold hatcheries, and reared identically as the experimental fish. Cage rearing lasted for 63 days. Growth rate , mortality, LDS and fish biomass were determined throughout of the experiment. The larvae attained the weight of 41 mg at the end of tank rearing. Fry obtained at the end of the cage rearing weighed from 1732 to 2023 mg (experimental fish) and from 475 to 648 mg (control fish). Stock mortalities amounted from 65 to 80 %. Experimental fish finished their larval development after 42 days, whereas a certain part of control group did not finished their larval development till the end of cage rearing. There were high values of fish biomass in cages in tank-and-cage rearing (from 2.39 to 3.24 kg/m3). The results of the experiment have showed that tank-and-cage rearing of producing coregonid stocking material may be applicable in eutrophic lakes.
Key words: COREGONID LARVAE, REARING, TANKS, CAGES