Browsing by Subject "Light intensity"

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    Continuous high light intensity can induce retinal degeneration in atlantic salmon, atlantic cod and european sea bass
    (2009) Vera, L.M; Migaud, H.; Fisiología
    Retinal photodamage has previously been studied in teleost fish but very few have been performed on aquaculture species. To study retinal damage, Atlantic cod (Gadus morhua), Atlantic salmon (Salmo salar) and European sea bass (Dicentrarchus labrax) were previously acclimated to a control 12L:12D photoperiod with standard experimental low light intensity (0.1 W/m2 , equivalent to 3.2 x 1013 photons /s /cm2 ) for at least 4 weeks and then kept under constant darkness (DD) for 3 days. Thereafter, fish were exposed to continuous high intensity light (51-380 W/m2 , equivalent to 1.63 x 1016 – 1.22 x 1017 photons /s /cm2 ) for 3, 7, 15 or 25 days before returning to a control 12L:12D photoperiod (same intensity than during acclimation period) to study retinal regeneration over a period of 30 days. Retinal damage was exclusively assessed through the analysis of morphometric parameters. Results showed the presence of light-induced damage in the three species examined, as well as recovery once the control photocycle was restored. Cod was the most light-sensitive species as demonstrated by early signs of retinal damage (from three days of exposure) and reduced photoreceptor layer thickness (PRos/is) (43.1% relative to basal value in comparison to 51.6% and 73.3% respectively in salmon and sea bass). However, once the light-dark cycle was resumed the retina recovered in the three species studied (after 15 days in cod and 30 days in salmon and sea bass). Exposure to continuous high intensity light also resulted in significantly increased plasma cortisol levels in cod at LL15 (13.4 ± 2.0 ng/ml) and sea bass at LL3 (120.6 ± 12.2 ng/ml) and LD15 (54.2 ± 7.1 ng/ml). These results have important welfare implications with regards to the use of artificial light in culture and should be considered when designing lighting protocols in the aquaculture industry.
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    Differential light intensity and spectral sensitivities of atlantic salmon, european sea bass and atlantic cod pineal glands ex vivo
    (2010) Vera, L.M.; Davie, A.; Taylor, J.F.; Migaud, H.; Fisiología
    Photoperiod is perceived by pineal photoreceptors and transduced into rhythmic melatonin signals. These rhythms can be influenced by light intensity and spectral content. In this study we compared the light sensitivity of Atlantic salmon, European sea bass and Atlantic cod by testing ex vivo the effect of different intensities and narrow bandwidth lights on nocturnal melatonin suppression by isolated pineal glands in a flow-through culture system. Using combinations of neutral density and bandpass interference filters we tested a range of light intensities (ranging from 1.22 x 1013 – 3.85 x 106 photons.s-1 .cm-2 ) and three wavelengths of 80 nm width (472, 555 and 661 nm corresponding to blue, green and red, respectively). Results showed clear species specific light intensity and spectral sensitivities, with cod being from 100 to 1000 times more sensitive than sea bass and salmon. Regarding the influence of spectrum, red light was less efficient on suppressing melatonin than blue and green in salmon but results were not as clear in the two other species studied. Finally, the first evidence of relative photoreception in teleosts was obtained in cod suggesting that the definition of illuminance thresholds (day/night perception) would depend on the day intensity. Indeed, a single order of magnitude increase or decrease in day intensity was shown to elicit a significant shift in the intensity response curve of night-time melatonin suppression. Taken together, this study demonstrated species specific light intensity and spectral sensitivities within temperate teleosts.
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    Influence of light intensity on plasma melatonin and locomotor activity rhythms in tench
    (2005) Vera, L.M.; López Olmeda, J.F.; Bayarri, M.J.; Madrid, J.A.; Sánchez Vázquez, F.J.; Fisiología
    Melatonin production by the pineal organ is influenced by light intensity, as has been described in most vertebrate species, in which melatonin is considered a synchronizer of circadian rhythms. In the case of tench, strict nocturnal activity rhythms have been described although the role of melatonin has not been clarified. In this study we investigated daily activity and melatonin rhythms under 12:12 light-dark (LD) conditions with two different light intensities (58.6 and 1091µW/cm2 ), and the effect of one hour broad spectrum white light pulses of different intensities (3.3, 5.3, 10.5, 1091.4 µW/cm2 ) applied at mid darkness (MD) on nocturnal circulating melatonin. The results showed that plasma melatonin in tench under LD 12:12 and high light conditions displayed a rhythmic variation, where values at MD (255.8 ± 65.9 pg/ml) were higher than at mid light (ML) (70.7 ± 31.9 pg/ml). Such a difference between MD and ML values was reduced in animals exposed to LD 12:12 and low light intensity. The application of one hour light pulses at MD lowered plasma melatonin to 111.6 ± 3.2 pg/ml (in the 3.3-10.5 µW/cm2 range) and to 61.8 ± 18.3 pg/ml (with the 1091.4 µW/cm2 light pulse) and totally suppressed nocturnal locomotor activity. These results showed that melatonin rhythms persisted in tench exposed to low light intensity although the amplitude of the rhythm is affected. In addition, it was observed that light pulses applied at MD affected plasma melatonin content and locomotor activity. Such a low threshold suggests that the melatonin system is capable of transducing light even under dim conditions, which may be used by this nocturnal fish to synchronize to weak night light signals (e.g. moonlight cycles)