Ultraviolet light and semi-recirculating systems in artificial incubation of noble crayfish (Astacus astacus) eggs: opportunities and limitations Antonı ´n Kouba, Hamid Niksirat, Iryna Kuklina, Milos ˇ Bur ˇic ˇ & Pavel Koza ´k South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses and Research Institute of Fish Culture and Hydrobiology in Vodn ˇ any, Faculty of Fisheries and Protection of Waters, University of South Bohemia in C ˇ eske ´ Bude ˇjovice,Vodn ˇ any, Czech Republic Correspondence: Antonı ´n Kouba, South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses and Research Institute of Fish Culture and Hydrobiology in Vodn ˇ any, Faculty of Fisheries and Protection of Waters, University of South Bohemia in C ˇ eske ´ Bude ˇjovice, Za ´tis ˇı ´ 728/II, CZ-389 25, Vodn ˇ any, Czech Republic. E-mail: akouba@frov.jcu.cz Abstract Development of artificial crayfish egg incubation is a milestone in intensive culture of crayfish as com- mercially important freshwater animals. This study evaluated experimental treatments combining con- tinuous UV lighting, a non-chemical antifungal treatment, with an initial formaldehyde bath for noble crayfish (Astacus astacus) eggs incubated in semi-recirculating systems, which requires less than 1 per cent the amount of water necessary for conventional flow-through systems. The one-time administration of a pre-incubation bath to reduce formaldehyde exposure was ineffective. Ultraviolet irradiation of recirculating water provided poor results (13.5% and 35.2% final survival rates to stage 2 juveniles) and led to deteriorating water quality. An inability of hatchlings to successfully moult and the occurrence of limb deformities was observed in UV-treated groups, and juvenile mor- tality was found across all experimental treat- ments. Keywords: astacid culture, formaldehyde, nor- mal microflora, oomycetes, rearing, water quality Introduction The rearing of freshwater crayfish is an important component of worldwide aquaculture (Holdich 1993), and artificial incubation of crayfish eggs is one of the milestones in intensive culture of these animals (Carral, Sa ´ez-Royuela, Celada, Pe ´rez, Melendre & Aguilera 2003; Gonza ´lez, Celada, Gar- cı ´a, Gona ´lez, Carral & Sa ´ez-Royuela 2009). Despite many advantages, artificial incubation presents at least two important challenges. The first is the development of effective antifungal treatments that are safe for cultured animals and farm staff as well as for the aquatic environment, and the second is the need for high quality water during long-term incubation. Regarding the former, the previously used mala- chite green is prohibited for aquaculture in the USA and EU (Celada, Carral, Sa ´ez-Royuela, Melendre & Aguilera 2004) because of a range of negative effects (Srivastava, Sinha & Roy 2004; Sudova, Machova, Svobodova & Vesely 2007). Formaldehyde has been found to be a potential alternative (Melendre, Celada, Carral, Sa ´ez-Royuel & Aguilera 2006), but its carcinogenicity and other harmful effects (van West 2006; Duhayon, Hoet, Van Maele-Fabry & Lison 2008), make its use better avoided. This situation has led to the search for alternatives (Carral, Gonza ´lez, Celada, Sa ´ez-Royuela, Melendre, Gonza ´lez & Garcia 2009; Policar, Smyth, Flanigan, Kouba & Koza ´k 2011). Attempts have been made to reduce the quantity of water needed through the use of flow-through incubation systems during artificial incubation of signal crayfish (Pacifastacus leniusculus) eggs. Sa ´ez- Royuela, Melendre, Celada, Carral, Gona ´lez, Gonza ´- lez and Garcı ´a (2009) raised the previously recom- mended egg density (6.6 eggs cm 2 ) in incubators © 2011 Blackwell Publishing Ltd 67 Aquaculture Research, 2013, 44, 67–74 doi: 10.1111/j.1365-2109.2011.03010.x