Influence of temperature and size on menthol anaesthesia in Chinese grass shrimp Palaemonetes sinensis (Sollaud, 1911)

Chinese grass shrimp, Palaemonetes sinensis (Sollaud, 1911), is an economically important freshwater shrimp in China and adjacent areas. It is advisable to use anaesthesia in this species for certain handling and shipping operations; however, there have been no investigations into the recommended dosages. Here, the influence of five menthol concentrations (varying from 100 to 500 mg/L) on three different size classes of P. sinensis were examined at 8, 12, 16, 20, 24 and 28°C. Induction and recovery times for each shrimp were recorded, and effects of temperature, size and menthol dose on induction and recovery times were observed. Results showed that menthol dose, water temperature and shrimp size significantly influence anaesthesia in P. sinensis. Induction time decreased linearly with increasing water temperature and concentration of menthol, and increased with body weight. However, recovery times lengthened with concentration and temperature, and became shorter with body weight. Average body weight of the shrimps generally decreased after anaesthesia. Mortality of shrimps was correlated with temperature, dose and size. These results suggest that menthol is an effective rapid anaesthetic for P. sinensis, but there may be some disadvantages, including slow recovery and possible mortality for small shrimps and at higher temperatures and dosages.