Illuminating Growth: How Light Spectra Influence Juvenile Steelhead Trout (Oncorhynchus mykiss) Growth and Metabolism

The diurnal variation in the sun's altitude alters the red-to-blue light spectrum ratio under identical water layers. This study explores how juvenile steelhead trout (Oncorhynchus mykiss) (initial weight: 34.67 g ± 2.69 g) responds to these fluctuating light conditions, focusing on growth, daily activity levels, and energy budget. During 16 weeks, the experiment was conducted to examine six lighting scenarios: 12 h white light followed by 12 h darkness (12W); 12 h blue light followed by 12 h darkness (12B); 12 h red light followed by 12 h darkness (12R); 1.5 h blue light, 9 h red light, and again 1.5 h blue light followed by 12 h darkness (3B9R); 3 h blue light, 6 h red light, and again 3 h blue light followed by 12 h darkness (6B6R); and 12 h combined blue and red lights followed by 12 h darkness (T12BR). The findings reveal that the 3B9R lighting condition notably enhanced specific growth rate (SGR), feed conversion efficiency (FCE), and growth energy allocation, while diminishing daily activity levels in steelhead trout. Conversely, under the 6B6R condition, there was a significant reduction in SGR and FCE, indicating that growth was inhibited. Under the 12R condition, despite the high activity and respiratory energy loss, the trout exhibited improved SGR and FCE with reduced fecal energy loss. The study suggests that 3B9R and 12R lighting conditions might be beneficial in commercial steelhead trout farming, potentially lowering costs and boosting production. These results offer valuable insights for the application of supplementary lighting technology in salmon aquaculture.