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THE IMPACT OF PHOTOPERIOD AND STOCKING DENSITY ON THE GROWTH AND SURVIVAL OF NARROW-CLAWED CRAYFISH (ASTACUS LEPTODACTYLUS Esch.) LARVAE
Dariusz Ulikowski, Tadeusz Krzywosz
The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. The aim of the study was to determine the impact of various photoperiods and stocking densities on the growth and survival of narrow-clawed crayfish larvae. The four-week rearing period was carried out in 50 dm3 tanks in a closed recirculating system. The tanks were stocked with larvae two weeks post hatch with an average body length of 11.2 ± 0.9 mm (TL) and weight of 32.3 ± 2.5 mg. There were three stocking densities (300, 600, and 1200 specimens m-2) and two photoperiods (groups L – 24-hour illumination and groups D – 24-hour darkness). The crayfish were fed ad libitum every 12 hours with granulated feed (45% protein, 6-12% lipid). The experiment indicated that photoperiod had a significant impact (P < 0.05) on the crayfish survival rate, while stocking density impacted growth. Crayfish survival was almost two times higher with 24-hour illumination than it was with 24-hour darkness at each of the stocking densities. The survival and the growth rate of crayfish decreased as the initial stocking density increased. The final biomass of the crayfish stocks reared in 24-hour darkness was similar for each of the stocking densities applied, but the biomass of stocks reared with 24-hour illumination increased along with the stocking densities used. This indicates that it is possible to apply initial densities even greater than 1200 specimens m-2 during crayfish rearing with 24-hour pond illumination.
Key words: NARROW-CLAWED CRAYFISH (ASTACUS LEPTODACTYLUS), REARING, LARVAE, PHOTOPERIOD, STOCKING DENSITY
CORRESPONDING AUTHOR:
Dariusz Ulikowski, Instytut Rybactwa Śródlądowego, Doświadczalny Ośrodek Zarybieniowy „Dgał", 11-610 Pozezdrze, Pieczarki 50, tel. +48 (89) 428 36 66;
e-mail: ulikowski@infish.com.pl