Photoperiodic mechanisms and rhythms of reproduction in the female rainbow trout

Abstract

The present work investigates the importance of circadian and circannual rhythms in the photoperiodic control of reproduction in the rainbow trout. Maintenance of groups of 20-30 female trout under continuous light (LL), constant long (18L:6D) or short (6L:18D) days and conditions of constant temperature (8.5-9.0°C) and feeding rates (0.5% body weight, day(-1)), starting in February, produced markedly different spawning periodicities during the first and subsequent years of treatment. At the end of the first year, spawning was advanced by up to 2 months in the fish under LL and 18L:6D and delayed by up to 5 months in those under 6L:18D when compared with the December spawning of control fish under ambient light. Continued exposure of the fish to the same photoperiod regimes produced cycles of spawning and peak levels of testosterone, oestradiol-17β and calcium (as an index of vitellogenin) at intervals of 150-170 days under LL and 18L:6D and 320-420 days under 6L:18D. The functional importance of these spawning cycles and their relationship to circannual rhythms and the control of reproduction is discussed.Exposure of fish to skeleton (6L:4D:2L:12D, 6L:6D:2L:10D and 6L:8D:2L:8D) and resonance (6L:42D, 6L:48D and 6L:54D) procedures produced ranges of spawning times up to two months in advance of control fish. Results with the resonance regimes, where fish received only a half the light-dark cycles and a quarter of the total daylight hours of those on ambient light cycles show that trout do not measure daylength and time by counting daily cycles or by hour-glass mechanisms. Collectively, these data support the proposition that rhythmic processes of photosensitivity are involved in the modulation of reproductive development in the rainbow trout and that circadian and circannual rhythms cooperate in the timing and entrainment of this cycle.

Quantitative genetic architecture of parasite-induced cataract in rainbow trout, Oncorhynchus mykiss

“…It is possible that, first, reduced growth or a lower condition in individuals with more severe cataracts led to a delay in maturity (Fleming, 1996). Second, given that the circadian rhythm is an essential stimulus in the maturation process (Duston and Bromage, 1986), the reproductive physiology of fish with severe cataracts may have been impaired because of the reduced perception of the light stimulus. Third, parasites might have directly influenced the host maturation process.…”

Chronobiology: implications for marine resource exploitation and management

“…However, some evidence of the phenomenon in fish has become available from aquaculture studies (Dustan and Bromage, 1986) as it has also for some polychaete worms (Olive, 1984;Bentley et al, 2001). Intuitively, there is a high probability of the widespread occurrence of endogenous circa-annual rhythmicity in animals living where annual environmental cycles prevail.…”

“…This is generally thought to be a more important aspect of light controlling fish development than, say, light intensity or spectral composition. With freshwater trout, experimental modification of the seasonally-varying cycle of day length has been used for the production of year-round supplies of eggs for commercial fish farms (Dustan and Bromage, 1986). Also, similar photoperiod manipulation is the tool most used by farms to control growth, reproduction and smoltification of Atlantic salmon (Berrill et al, 2003), though the physiological mechanisms underlying such commercial manipulations are still poorly understood.…”

Suprachiasmatic Nucleus and Photic Entrainment of Circannual Rhythms in Ground Squirrels

“…These rhythms &dquo;free-run&dquo; with periods (T's) different from 12 months and can be entrained to a T of 365 days by alternating sequences of long and short daylengths in sheep (reviewed in Karsch et al, 1991), avian species (Gwinner, 1971(Gwinner, , 1986Follett and Follett, 1981), deer (for a review, see Goss, 1983), and trout (Sundararaj et al, 1982;Duston and Bromage, 1986, 1987. In contrast, photoperiod has long been considered ineffective as a zeitgeber for entraining circannual rhythms of the goldenmantled ground squirrel, Spermophilus lateralis (e.g., Pengelley and Fisher, 1963;Asmundson, 1969, 1970).…”