Physiological and Transcriptomic Responses to Cold Stress in Taiwan Loach (Paramisgurnus dabryanus ssp. Taiwan)

The Taiwan loach (Paramisgurnus dabryanus ssp. Taiwan) is a popular cultured fish in southern China due to its rich nutritional content and rapid growth. Oxidative stress and homeostatic imbalance induced by low temperature are among the key factors restricting its large-scale aquaculture. Therefore, it is of great significance to investigate the oxidative stress damage and the adaptive mechanisms employed by this species in response to low temperature. In this study, the water temperature was lowered from 24 °C to 8 °C at a rate of 2 °C/h. Afterwards, the temperature was held at 8 °C for two durations: 12 h and 48 h. Antioxidant indices indicated that the Taiwan loach suffered from oxidative stress damage at the 12 h stage, but the antioxidant enzyme defense system was not fully activated. As the cold stress extended to 48 h, the activities of total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) increased significantly (p < 0.01). Histological observations revealed that the livers exhibited cellular vacuolation, sinusoid congestion and karyolysis under cold stress. Transcriptomic data revealed that the Taiwan loach underwent adaptive alterations in response to low temperature through diverse pathways. We speculate that, at low temperature, the Taiwan loach may, on the one hand, regulate lipid metabolism to maintain cell membrane fluidity and meet energy demands, and, on the other hand, reprogram protein synthesis and processing to avert the overaccumulation of misfolded proteins. In addition, it also adopts a strategy of lysine and polyamine accumulation. This study provides a novel theoretical basis for breeding cold-tolerant varieties of Taiwan loach and optimizing overwintering aquaculture management.