*2.2. Sample Collection*

Samples were collected in two different weather conditions, sunny and cloudy. Four sampling times (6:00, 12:00, 18:00 and 24:00) were set for one daily cycle with three parallel ponds. The three fish were taken from each parallel pond. The environmental conditions at each sampling time are shown in Table 1. Fish were deprived of feed for 24 h before the sampling was conducted. Three fish were randomly selected for sampling at each time point. Samples were collected under dim red light at night. After anesthesia with eugenol (80 mg·L<sup>−</sup>1), the body length and weight were measured, and the liver tissue was quickly collected, snap-frozen in liquid nitrogen and preserved at −80 ◦C until use.


**Table 1.** Environmental indicators.

#### *2.3. Total RNA Extraction and cDNA Synthesis*

The tissue samples were homogenized in a centrifuge tube containing 1 mL of Trizol (Invitrogen, Carlsbad, CA, USA) and extracted total tissue RNA according to the instructions. The quality and quantity of total RNA were tested using agarose gel electrophoresis and a Micro UV spectrophotometer (Biotec Biotechnology Co., Ltd., Beijing, China). Reverse transcription was performed on 1 μg of total RNA using an EasyScript® All-in-One First-Strand cDNA Synthesis SuperMix (All-Strand Biotechnology Co., Ltd., Beijing, China).
