Introduction
Ornamental fish industry is a fast-growing multibillion dollar sector worldwide with more than 1500 species available. The market value of ornamental fish depends on visual criteria such as size, body shape, fins and skin color. The coloration of fish is related with several types of pigmented cells and chromatophores connected to the neural system (Urban et al., 2013). There are many researches on fish coloration through dietary administration of various expensive carotenoids from synthetic or extracted natural sources. The present study is projected to reveal a potential condensation in fish skin color via neural effects of binaural beats.
Materials and methods
A 90 days trial was conducted with red variety of zebrafish (Danio rerio) in triplicate glass aquariums with 24±1ºC water temperature, fluorescent lighting (14L:10D), constant aeration and filtration. Fish were fed twice a day with commercial aquafeeds. Three treatment groups were subjected to binaural audio file complex through directional speakers. The control group was given no audio signals. At the end of the trial, to assess any difference in skin color with a noninvasive method, randomly selected fish from each group were photographed and digital images were analyzed with the software Expertomica FISCEAPP (Urban et al., 2015).
Results and discussion
Whole body images of fish were processed using software and images were evaluated in the RGB (Red, Green, Blue), HSV (Hue, Saturation, Value), and CIE L*a*b (lightness, position between red and green, position between yellow and blue) color space systems using the value of the dominant wavelength. Statistical analyses were performed using IBM SPSS v.22.0 software.
Color saturation values were found highest in Group 2 and lowest in Group 1 but there was no linear alteration based on treatment time. The dominant color wavelength was found to be between 603 and 611 nm (a mean of 606 nm) corresponding to an orange color. Decreases in the Green and Blue components of the RGB system resulted in a visual red color change in Group 1 compared to the Control and other experimental groups. In contrary to RGB system, a contradictory trend was seen in the CIE L*a*b* system where increasing a* and b* values were not linearly correlated with exposure time and the control group was found to display higher values indicating red and yellow. As evaluated with the HSV color system Group 1 reflected higher Saturation level indicating intenser red color and a linear decrease was found while treatment time becomes longer.
Pigmentation of muscle and skin of fish has always been in the spotlight for aquaculture and created a broad global market. Numerous researches have been performed to find a more effective but cheaper, healthy and eco-friendly carotenoid source and all have been focused on dietary supplements from synthetic astaxanthin, crustacean wastes, microalgae, yeast and plant seeds (Saito and Regier, 1971; Tangerås and Slinde, 1994; Lorenz and Cysewski, 2000; Yi et al., 2014; Kang et al., 2015). The present study is being the first to evaluate any possible improvement in fish skin color through remote affect on fish neural mechanism by using an electronic integrated system. The results show the skin color in fish would be affected by binaural beats and further extensive research could increase the knowledge on the mechanism of action and help to optimize the treatment procedure.
References
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