Influence of light colours on growth and stress response of rainbow trout (Oncorhynchus mykiss) under laboratory conditions

Effects of Light Spectra on Nutritional Composition in Juvenile Sinonovacula constricta (Lamarck 1818) and Transcriptomic Analysis

The razor clam Sinonovacula constricta, a commercially important and nutritionally valuable bivalve species, has been found to display notable responses to different light spectra. While previous research has highlighted the influence of light spectra on the growth, feeding rate, and various physiological characteristics of S. constricta, its impact on the biochemical composition of this species remains unclear. Herein, we investigated the proximate, fatty acid, and amino acid compositions of S. constricta cultured under various light spectra, including white, violet, blue, cyan, green, yellow, red, and darkness. Furthermore, we explored the potential molecular mechanisms underlying these observations through transcriptomic analysis. The results indicate that the light spectrum has a significant impact on the growth, biochemical composition, and gene expression of juvenile S. constricta. Specifically, culturing S. constricta under the yellow light led to improved growth rate (1.09 ± 0.03%/day), higher levels of carbohydrate (26.27% ± 0.49%), crude lipid (11.99% ± 0.23%), energy contents (14,611.34 ± 1,067.01 kJ/kg), and essential amino acids (15.22 ± 0.01 g/kg), as well as increased proportions of polyunsaturated fatty acids (12.38 ± 0.31 µg/mg). These findings suggest that yellow light may play a crucial role in enhancing the nutritional quality of S. constricta. Moreover, the transcriptomic analysis revealed that the yellow light treatment upregulated pathways related to fatty acid biosynthesis, glycine, serine, and threonine metabolism and fatty acid metabolism. This indicates that yellow light may influence nutrient metabolism regulation in S. constricta, potentially leading to the observed changes in biochemical composition. Overall, our study recommends cultivating juvenile S. constricta under yellow light to optimize their growth and nutritional value. Further research could delve deeper into the molecular mechanisms underlying the effects of different light spectra on S. constricta to enhance our understanding of how light influences aquaculture practices and the nutritional quality of seafood products.

Disparities in Body Color Adaptability and Ambient Light Color Preference between Wild and Hatchery-Reared Marbled Rockfish (Sebastiscus marmoratus)

Hatchery rearing significantly influences the phenotypic development of fish, with potential adverse effects for the post-release performance of hatchery-reared individuals in natural environments, especially when targeted for stock enhancement. To assess the suitability of releasing hatchery-reared fish, a comprehensive understanding of the phenotypic effects of captive rearing, through comparisons with their wild conspecifics, is essential. In this study, we investigated the divergence in body coloration between wild and hatchery-reared marbled rockfish Sebastiscus marmoratus. We examined the selection preferences for different light colors and assessed the impact of different ambient light colors on the morphological color-changing ability of juvenile marbled rockfish. Our findings revealed significant differences in body color between wild and hatchery-reared marbled rockfish. The hue and saturation values of wild marbled rockfish were significantly higher than those of their hatchery-reared counterparts, indicative of deeper and more vibrant body coloration in the wild population. Following a ten-day rearing period under various light color environments, the color of wild marbled rockfish remained relatively unchanged. In contrast, hatchery-reared marbled rockfish tended to change their color, albeit not reaching wild-like coloration. Light color preference tests demonstrated that wild juvenile marbled rockfish exhibited a preference for a red-light environment, while hatchery-reared individuals showed a similar but weaker response. Both wild and hatchery-reared marbled rockfish displayed notable negative phototaxis in the presence of yellow and blue ambient light. These results highlight the impact of hatchery rearing conditions on the body color and morphological color-changing ability, and provide insight into light color selection preferences of marbled rockfish. To mitigate the divergence in phenotypic development and produce more wild-like fish for stocking purposes, modifications to the hatchery environment, such as the regulation of ambient light color, should be considered.

Colour as a behavioural guide for fish near hydrokinetic turbines

Hydropower is a traditional and widespread form of renewable energy and vertical axis turbines are an emerging technology suitable for low to medium velocity water bodies such as rivers. Such devices can provide renewable power to remote communities but may also contribute to fragmenting already poorly connected riverine habitats and the impact could be particularly pronounced for migratory diadromous aquatic species such as salmonids by limiting their ability to pass the turbines. Optimising the design of such turbines is therefore essential to mitigate their impact on aquatic fauna. One easily altered property that does not impact turbine performance is blade colour. Here, juvenile rainbow trout (Oncorhynchus mykiss) free swimming within a flume were monitored in the presence of a vertical axis turbine that was either stationary or rotating, and coloured white or orange. The orange colour of the turbine affected behaviour by increasing turbine avoidance and decreasing the number of potentially harmful interactions with the turbine when it was rotating, whilst not affecting passage or mobility of the trout compared to the white turbine. Visibility is therefore a potentially useful tool in mitigating the environmental impact of hydrokinetic turbines.

Effects of Colored Light on Growth and Nutritional Composition of Tilapia, and Biofloc as a Food Source

Light stimulation and biofloc technology can be combined to improve the efficiency and sustainability of tilapia production. A 73-day pilot experiment was conducted to investigate the effect of colored light on growth rates and nutritional composition of the Nile tilapia fingerlings (Oreochromis niloticus) in biofloc systems. The effect of colored light on the nutritional composition of bioflocs as a food source for fish was measured. Three groups were illuminated in addition to natural sunlight with colored light using RGB light emitting diodes (LEDs) with peak wavelengths (λ) of 627.27 nm for red (R), 513.33 nm for green (G), and 451.67 nm for blue (B) light. LED light intensity was constant (0.832 mW / cm 2 ), and had an 18-h photoperiod of light per day throughout the study. The control group was illuminated only with natural sunlight (natural). Tilapia had an average initial weight of 0.242 g. There was a significant effect of colored light on tilapia growth and composition. The R group showed the best growth rate, highest survival, and highest lipid content. The B group showed homogeneous growth with the lowest growth rate and lipid content, but the highest protein level. On the other hand, the biofloc composition was influenced by the green light in the highest content of lipids, protein, and nitrogen-free extract.

Relevance of Light Spectra to Growth of the Rearing Tiger Puffer Takifugu rubripes

In fish, light (photoperiod, intensity and spectra) is main regulator in many physiological actions includinggrowth. We investigate the effect of light spectra on the somatic growth and growth-related gene expression in the rearing tiger puffer. Fish was reared under different light spectra (blue, green and red) for 8 weeks. Fish body weight and total length were promoted when reared under green light condition than red light condition. Expression of somatostatins (ss1 and ss2) in brain were showed higher expression under red light condition than green light condition. The ss3 mRNA was observed only higher expression in blue light condition. Expression of growth hormone (gh) in pituitary was detected no different levels between experimental groups. However, the fish of green light condition group was showed more high weight gain and feed efficiency than other light condition groups. Our present results suggest that somatic growth of tiger puffer is induced under green light condition because of inhibiting ss mRNA expression in brain by effect of green wavelength.

Impact of different colours of artificial light at night on melatonin rhythm and gene expression of gonadotropins in European perch

The distribution and intensity of artificial light at night, commonly referred to as light pollution, is consequently rising and progressively also ecological implications come to light. Low intensity light is known to suppress nocturnal melatonin production in several fish species. This study aims to examine the least suppressive light colour for melatonin excreted into the holding water and the influence of different light qualities and quantities in the night on gene expression of gonadotropins in fish. European perch (Perca fluviatilis) were exposed to light of different wavelengths during the night (blue, green, and red). Melatonin concentrations were measured from water samples every 3h during a 24h period. Gene expression of gonadotropins was measured in perch exposed to different light colours and was additionally examined for perch subjected to different intensities of white light (0 lx, 1 lx, 10 lx, 100 lx) during the night. All different light colours caused a significant drop of melatonin concentration; however, blue light was least suppressive. Gene expression of gonadotropins was not influenced by nocturnal light of different light colours, but in female perch gonadotropin expression was significantly reduced by white light already at the lowest level (1 lx). We conclude that artificial light with shorter wavelengths at night is less effective in disturbing biological rhythms of perch than longer wavelengths, coinciding with the light situation in freshwater habitats inhabited by perch. Different light colours in the night showed no significant effect on gonadotropin expression, but white light in the night can disturb reproductive traits already at very low light intensities. These findings indicate that light pollution has not only the potential to disturb the melatonin cycle but also the reproductive rhythm and may therefore have implications on whole species communities.