Harmful impact of filamentous algae (Spirogyra sp.) on juvenile crayfish

The aim of this study was to determine the impact of filamentous algae on the growth and survival of juvenile narrow-clawed crayfish, Astacus leptodactylus (Esch.), in rearing basins. Three stocking variants were used: A - basins with a layer of filamentous algae without imitation mineral substrate; B - basins with a layer of filamentous algae with imitation mineral substrate; C - basins without filamentous algae but with mineral substrate. The crayfish were reared from June 12 to October 10 under natural thermal conditions and fed a commercial feed. The results indicated that the presence of the filamentous algae did not have a statistically significant impact on the growth of the juvenile crayfish (P > 0.05). The presence of the filamentous algae had a strong negative impact on juvenile crayfish survival and stock biomass (P < 0.05). The layer of gravel and small stones that imitated the mineral substrate of natural aquatic basins somewhat neutralized the disadvantageous impact the filamentous algae had on the crayfish.