Photoperiodic induction of ovarian maturation in crayfish Procambarus clarkii is mediated by extraretinal photoreception

Abstract

The current study was carried out to investigate whether the photoperiodic induction of ovarian maturation in crayfish is based on a photosensitive rhythm related to extraretinal photoreceptors. To test this, two batches of 61 juvenile crayfish Procambarus clarkii consisting of (1) intact organisms and (2) animals lacking retina and lamina were exposed to 24h light-dark cycles of different photoperiodic schedules based on a night-break protocol for 3 months. Both batches of crayfish showed the greatest ovarian maturation (size, color, degree and size of oocytes) when the light pulse interrupted the scotophase at 21:00 and 05:00, showing a bimodal photoinducible rhythm. Results of the current study indicate that crayfish ovarian maturation depends on a photoinducible rhythm with two possible states that is related to the circadian clock of crayfish. This phenomenon is mediated by extraretinal photoreceptors. Results are interpreted in the light of models of external coincidence.