UTTAR PRADESH JOURNAL OF ZOOLOGY

LED lights are widely used in zebrafish research institutions and aquatic culture facilities worldwide; however, limited information is available on the effects of different wavelengths on early larval development. This study assessed the effects of five LED wavelengths (white, blue, green, yellow and red) on the early larval development of Danio rerio, with a non-irradiated group serving as the control. Larvae were photographed using bright-field microscopy at two developmental stages (5 days post-fertilisation [dpf] and 10 dpf) to determine the numbers of normally developed, abnormally developed and deceased larvae. The results demonstrated that blue LED irradiation had the greatest effect on larval morphology at both evaluation stages. At 5 dpf, only 63% of larvae irradiated with blue LED appeared normal, compared with 90% of control larvae; this value declined to 43% by 10 dpf, with a mortality rate of 30%. Abnormalities observed in blue LED-irradiated larvae included yolk sac oedema (YSE), pericardial oedema (PE), spinal curvature (SC), tail curvature (TC) and microphthalmia (MO). Yellow LEDs exhibited the next highest degree of phototoxicity. Red and green LEDs produced considerably less phototoxicity, with 78% and 77% of larvae, respectively, appearing normal at 5 dpf. Importantly, the data indicated that phototoxic outcomes increased in severity from 5 to 10 dpf in all exposed treatment groups, indicating cumulative rather than acute effects. These findings indicate that LED wavelength should be treated as a formally controlled variable when LED light sources are used in zebrafish research and suggest that red or green LEDs may be safer options for aquaculture and larval-rearing applications.