IMPACT OF FOOD SUPPLY FREQUENCY AND THE NUMBER OF SHELTERS ON THE GROWTH AND SURVIVAL OF JUVENILE NARROW-CLAWED CRAYFISH (ASTACUS LEPTODACTYLUS ESCH.)
Dariusz Ulikowski, Tadeusz Krzywosz
Department of Lake Fisheries, The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. The aim of the research was to study the impact food supply frequency and the number of shelters has on the growth and survival of juvenile narrow-clawed crayfish, Astacus leptodactylus Esch., fed formulated feed and to determine the dependence of total body length (LT) on the carapace length (LC). In the first experiment, four food supply frequencies were tested for 28 days at a crayfish stocking density of 300 indiv. m-2. Feed was delivered at intervals of 12 h (08:00 and 20:00), 24 h (20:00), 48 h (20:00) and 96 h (20:00). In the second experiment four different numbers of shelters in the tanks were tested for 30 days at a crayfish stocking density of 1500 indiv. m-2 (0, 60, 150, and 300 shelters m-2). Feeding frequency had a significant impact on crayfish body weight, specific growth rate (SGR), and relative growth rate (RGR) (P < 0.05). The highest values of these parameters were obtained at food supply rates of 12 and 24 h (82.9 mg, 3.6% day-1, 274% and 85.2 mg, 3.7% day-1, 282%), while the lowest values were noted for the longest food supply interval of 96 h (63.6 mg, 2.7 % day-1, 211%). The impact of various food supply frequencies on the survival of the stock was insignificant (P > 0.05). The number of shelters had a highly significant impact on survival and stock biomass (P < 0.05). The highest survival rate and stock biomass (31.5% and 57.9 g m-2, respectively) was noted in the variant with the most shelters (300 shelters m-2), while the lowest values (16.4% and 25.2 g m-2) were noted in the control variant (tank without shelters). The impact of the various numbers of shelters on crayfish growth and cheliped injury was not statistically significant (P > 0.05). The mean value of the proportion between total body length (LT) and the carapace length (LC) was 1.82 (variation coefficient V = 4.56%). There was a highly significant linear dependence among the morphometric indicators mentioned previously (P < 0.001, r = 0.9209), which was described by the following equation: LT = 1.6009 LC + 1.8662.
Key words: NARROW-CLAWED CRAYFISH (ASTACUS LEPTODACTYLUS), REARING, SHELTER, FEEDING FREQUENCY, GROWTH, SURVIVAL
Dr inż. Dariusz Ulikowski, Instytut Rybactwa Śródlądowego, Doświadczalny Ośrodek Zarybieniowy „Dgał“, 11-610 Pozezdrze, Pieczarki 50; Tel./Fax: +48 87 4283666;