Effect of water temperature on the development of Portunus trituberculatus larvae in the off-season breeding mode (Decapoda, Portunidae)

Abstract To clarify the influence of different water temperatures on the development of Portunus trituberculatus (swimming crab) larvae during off-season (early autumn) breeding, a gradient of four rearing temperatures of 27, 29, 31 and 33°C was set up, and the effects of water temperature on larval development were systematically compared. The results showed that the moulting cycle (MC) from the zoea 1 (Z 1 )-zoea 2 (Z 2 ) stage was not significantly affected by water temperature ( ), remaining at approximately 3 days. However, in the Z 2 -megalopa (M) stage, the MC in the 31°C group was consistently the shortest. The total developmental duration and total effective cumulative temperature during Z 1 -M in the 31°C group were the lowest at 9.97 days and 250 days · °C, respectively. According to the equation of water temperature and larval development rate, the development rate was the fastest when the water temperature was 31°C. As the water temperature increased, the survival rate (SR) of larvae at various stages gradually decreased. The SR of the 27°C group was consistently significantly higher than that of the 33°C group ( ), especially in the M stage, where the SR of the 33°C group was only 2%, which was significantly lower than that of the 27°C and 29°C groups ( ). Among the antioxidant indexes, both superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) were the lowest in the 29°C group at 315.75 U/mg protein and 0.36 mmol/g protein, respectively, and both were significantly lower than those in the 33°C group ( ). Catalase (CAT) and glutathione peroxidase (GSH-PX) were both the lowest in the 31°C group, and in this group the CAT was significantly lower than in the 33°C group, and GSH-PX was significantly lower than in the 27°C group ( ). For malondialdehyde (MDA) content, the four groups were basically maintained at about 2.5 nmol/mg protein, and there was no significant difference ( ). In terms of digestive enzyme activity, the activity of lipase (LPS) was basically maintained at 1.93 U/g protein. The other four digestive enzyme activity differences were mainly reflected in that the 31 and 33°C groups maintained relatively higher levels than the 27 and 29°C groups, especially the activities of α -amylase (AMS), and cellulase (CL) in the 33°C group, which were significantly higher than those in the 27 and 29°C groups ( ). Comprehensive indicators indicate that a water temperature between 29 and 31°C is the appropriate temperature for the development of the larvae of off-season breeding swimming crabs.