Author:

Keywords:

Crayfish, Light, Animal welfare

Abstract:

Noble crayfish (Astacus astacus) are freshwater crustaceans of European streams, rivers and lakes that frequently hide in dark places and naturally explore new environments. In a study by Fossat et al. (2015) a paradigm was validated to assess stress by using a subaquatic dark-light plus maze placing red swamp crayfish (Procambarus clarkii) in a conflicting situation between its innate curiosity for novel environment and its aversion for light. The experimentally stressed animals showed less explorative behaviour and remained preferentially in the dark arms, a response similar to the anxiety-like behaviour observed in rodents. We used the preference test on noble crayfish that were housed in tanks in different light conditions in order to investigate the welfare consequences. 468 crayfish were housed in social groups of 26 individuals divided over 18 tanks in two different light intensities (weak light: 38 lux; bright light: 761 lux) with 3 different light spectrums (cold white (CCT ≈ 5500K), warm white (CCT ≈ 2600 K) and neutral (CCT ≈ 3800 K)) over a period of six months. The animals had access to shelter places to hide. At night they had fourteen hours of complete darkness. In the plus maze the measured values in the dark/light branches were 21 versus 550 lux. We found that the crayfish kept in low lux conditions spent 7.87% (SD=9.48, p value Mann-Whitney-U test = 0.098) more time in the light arms of the plus maze than those kept under high lux. The spectrum of the light had no effect (p-value Kruskal-Wallis test = 0.715) This suggests that there is a trend in crayfish to show less anxious behaviour when being housed under low light conditions during the day, even when given the possibility to seek cover. The light intensity could be a factor to consider to ameliorate crayfish welfare.