Abstract

In fish, polymorphonuclear leucocytes (neutrophils or heterophils), macrophages and lysozyme are part of the non-specific defence mechanisms of the host when faced with pathogenic micro-organisms. To investigate the effect of artificial photoperiods on this defence system, trout were exposed during 142 days to one of three artificial photoperiods: LD 12:12, LD 24:0 and LD: 14:10. The blood / nitro-blue tetrazolium in vitro method was used to measure production of oxidative radicals and the turbidimetric method to assess plasma lysozyme concentration. A significant reduction in radical production was obtained at 7 days in the LD 24:0 and LD 14:10 groups and an increase in lysozyme concentration was observed in the LD 24:0 photoperiod treatment at 7 days and at 30 days for LD 14:10. These results are indicative of important consequences in the trout's susceptibility to diseases during application of artificial photoperiods, a technology widely used in pisciculture to alter maturation and enhance growth.