Abstract
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.
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