Possibilities of artificial incubation of signal crayfish (Pacifastacus leniusculus Dana) eggs at high densities and reduced flow rate using formaldehyde as antifungal treatment

The aim of this study was to determine the possibilities of increasing egg density in artificial incubation using low flow rates. Eggs of signal crayfish (Pacifastacus leniusculus) were incubated at three densities: 6.6, 20 and 42 eggs cm− 2 and two flow rates: 0.5 and 1 l min− 1 (0.0095 l cm− 2 min− 1 and 0.019 l cm− 2 min− 1, respectively). Formaldehyde doses of 3000 and 2500 ppm were administered as antifungal treatment. In experiment 1, the best survival to stage 2 juvenile (84.3%) was obtained with the administration of 3000 ppm of formaldehyde at a density of 6.6 eggs cm− 2, but differences were not significant either with a higher density (20 eggs cm− 2) or with a lower formaldehyde concentration (2500 ppm). In experiment 2, the best final survival (88.8%) was obtained with the administration of 2500 ppm of formaldehyde at a density of 20 eggs cm− 2, and a flow rate of 0.5 l min− 1 (0.0095 l cm− 2 min− 1), without significant differences either with the same density and a flow of 1 l min− 1 (0.019 l cm− 2 min− 1), or with the density of 42 eggs cm− 2 (around 86%). The progressive reduction of formaldehyde concentration we have tested may have found its limit at 2500 ppm since, although was shown to be effective, a light fungal growth could be observed. Nevertheless, with 3000 ppm the growth of fungi was kept out completely with densities up to 20 eggs cm− 2. Antifungal treatment seems to be a key factor to make feasible artificial incubation of crayfish eggs at high densities such as 42 eggs cm− 2, even with a limited water flow.