Ambient ultraviolet-B exposure brings quantum changes in phenotypic and molecular signatures of the embryo of a high-altitude fish, Tor putitora

Abstract

Effects of environmentally relevant ultraviolet B (UVB) light on the embryonic development of a high-altitude dwelling endangered fish, Tor putitora (golden mahseer), were investigated for the first time. For that, three sets of embryos (in triplicates) were exposed to various ambient UVB light doses (1, 2 and 3 W/m², corresponding to 3.6, 7.2 and 10.8 kJ/m²/day) for 1 h at two different embryonic stages (1 hpf—hours post fertilization and 32 hpf). Another set of embryos was exposed to visible light for the same duration and served as the light control (LC), and the last set was kept under ideal dark conditions for incubation (the dark control, DC). The results showed that the higher levels of UVB light (> 2 W/m²) decreased the hatching rate and survival of embryos and hatchlings, extended the hatching window or hatching time and caused embryonic and hatching deformities. The qPCR analysis revealed upregulation of genes such as nf-kb2, il-1β, tnfα, tlr5, nrf2, bcl2, caspase9, p53, ddb2, mmp13a, mc1r and hsp70 in a dose-dependent manner upon UVB exposure. Overall, the high ambient level of UVB exposure (3 W/m², equivalent to 10.8 kJ/m²/day) in golden mahseer embryos proved to be lethal or sub-lethal, which were mediated by (or related to) immunological changes, oxidative stress, apoptosis, DNA damage and aberrant development. Further, harmful effects of UVB were found to be stage-dependent and were more significant at 32 hpf. The study is the first preliminary report, at the molecular level, on the impact of environmentally occurring UVB on the embryonic development of an endangered fish species, the golden mahseer.