A COMPARISON OF SURVIVAL AND GROWTH IN JUVENILE ASTACUS LEPTODACTYLUS (ESCH.) AND PACIFASTACUS LENIUSCULUS (DANA) UNDER CONTROLLED CONDITIONS

The aim of this study was to compare survival and growth of juvenile narrow-clawed crayfish (Astacus leptodactylus) and signal crayfish (Pacifastacus leniusculus) fed only with experimental pellets (45% of proteins, 6% of fat, 20% crude fibre) under controlled conditions. The animals were reared in 12 (50 l) circular plastic tanks, the narrow-clawed crayfish set-ups being designated A1 and A2, the signal crayfish set-ups P1 and P2. The initial stocking densities for each species were 600 (A1, P1) and 1,200 (A2, P2) juveniles stage 2 per square metre for each set-up in three replicates. The experiment lasted 92 days under continuous photoperiod (L:D 24:0; 100 LUX) conditions at a temperature of 22.0 ± 0.1°C and an oxygen saturation > 90%. One shelter (plastic tube) was provided for 2 crayfish in each set-up. The highest survival rate was obtained for signal crayfish from set-up P1 (47.5%), the lowest for narrow-clawed crayfish from set-up A2 (22.8%). Crayfish survival evidently depends on the stocking density: in set-ups A1 and P1 it was about 16% higher than in set-ups A2 and P2 (P < 0.05). Mortality was significantly higher (P < 0.05) in both species during the first 30 days of the experiment (48-77% of the total mortality) than during the subsequent two months of the experiment (< 20% of the total mortality). The final body size was the largest in narrow-clawed crayfish from set-up A1 (799 mg, 29.2 mm) and the smallest in signal crayfish from set-up P2 (534 mg, 26.5 mm). Specimens of narrow-clawed crayfish were larger than signal crayfish, and the specimens of both species in set-ups A1 and P1 were larger than those in set-ups A2 and P2. During the first 30 days of the experiment the specific growth rate (SGR) of both species in all set-ups was twice the value reported during the subsequent two months (P < 0.05)

Growth, cannibalism, and survival relations in larvae of European catfish, Silurus glanis (Actinopterygii: Siluriformes: Siluridae)—attempts to mitigate sibling cannibalism

Background. Under culture conditions, intra-cohort cannibalism is one of the main factors that affects the growth and survival of fishes, especially during the early life stages of carnivorous species. Cannibalism is chiefly influenced by environmental factors, but parental effects cannot be excluded. The complete elimination of cannibalism in the larviculture of carnivorous fish species is virtually impossible, but it may be possible to mitigate its impact through a better understanding of the extrinsic and intrinsic factors that affect the intensity of cannibalism. The presently reported study had two complementary objectives: a) it examined how the growth–cannibalism–survival dynamics in cultured larvae of European catfish, Silurus glanis Linnaeus, 1758, is affected by maternal influence, and b) it evaluated the possibility of reducing cannibalism while supplementing food with tryptophan (TRP), which is a precursor of serotonin that has a becalming effect on fish. Materials and methods. Two 30-day experiments were conducted (0L : 24D, 26.5–27.0°C). In the first experiment, 3–day old larvae of European catfish originating from four female parents (f1, f2, f3, and f4) were cultured in full siblings groups. In the second experiment, larvae from all four progenies were reared together and fed commercial diets supplemented with different doses of tryptophan (T0, T1, T2). Fish mortality including cannibalism, growth, and biomass were estimated every 10 days during both experiments. Results. In both experiments, cannibalism was the main cause of mortality and losses to type II (complete) cannibalism were higher than those caused by type I (incomplete) cannibalism. No maternal influence on cannibalistic behaviour was found. Tryptophan supplementation had no significant effect on fish growth or survival. Conclusion. The results of presently reported studies confirmed that cannibalism is an important factor affecting survival in larviculture of European catfish. Controlled conditions used in initial rearing of European catfish larvae, significantly enhanced the survival of juvenile catfish in comparison to traditional pond culture