Transcriptomic responses to low temperature stress in the Nile tilapia, Oreochromis niloticus.

The Nile tilapia, Oreochromis niloticus, is a species of high economic value and extensively cultured. The limited stress tolerance of this species to a low temperature usually leads to mass mortality and great loss. Nevertheless, there is limited information on the molecular mechanisms underlying the susceptibility to low temperature in the tilapia. In this study, tilapia was treated at 28 °C to a lethal temperature of 8 °C by a gradual decrement. Transcriptomic response of the immune organ, kidney, in tilapia was characterized using RNA-seq. In total, 2191 genes were annotated for significant expression, which were mainly associated with metabolism and immunity. Pathway analysis showed that immune-related pathways of phagosome and cell adhesion molecules (CAMs) pathway were significantly down-regulated under low temperature. Moreover, ferroptosis, a significantly changed pathway involved in tissue damage and acute renal failure, is reported here for the first time. The levels of serum parameters associated with kidney damage such as urea and uric acid (UA) increased significantly under low temperature. The immunofluorescence staining of the kidney showed that cell apoptosis occurred at low temperature. The results of the present study indicate that exposure to low temperature can cause kidney disfunction and down-regulate the immune-related pathway in the kidney of tilapia. This study provides new insight into the mechanism of kidney damage in fish under low temperature.