The effect of continuous light and compressed photoperiods on growth and maturation in lumpfish Cyclopterus lumpus

From an aquaculture point of view, control of the sexual maturation cycle is critical for a sustainable production of the species. For year-round reliable production of juvenile lumpfish of the appropriate size for stocking salmon cages, there is a need for basic and applied knowledge on the control of sexual maturation in cultured lumpfish broodstock. Lumpfish (initial size 219 g and 16.9 cm) were reared under advanced simulated natural photoperiod (SLDN, control group) for Tromsø (70°N). In addition there were two groups exposed to continuous light from April 2014 to January 2015 (PP3) and from April 2014 to April 2015 (PP6) followed by 8 week decline in hours of light from 24 to 4 h (autumn signal) and subsequent 8 week rise from 4 to 24 h (spring signal). Exposure of lumpfish to continuous light followed by an autumn-spring signal stimulated somatic growth and affected age at first maturity in females. The growth enhancing effect of continuous light lasting for approximately six months in females compared to one month in the males. Spawning colouration and running milt was seen in males in all three photoperiod groups from September 2014 onwards indicating that maturation started prior to the experimental treatment. In the females spawning time, egg volume and hatching success varied between the photoperiod groups. No spawning occurred in the SLND group, whereas spawning was seen in both PP female groups 3-6 months after the onset of short autumn-short spring photoperiodic signal. Hatching success was higher in the PP3 group (83.4%) compared to the PP6 group (72.3%). The current findings are the first step in the development of photoperiod regimes which may provide simple and effective off-season maturation in lumpfish.