To investigate the effects of body size and water temperature on feeding and growth in the sea cucumber Apostichopus japonicus (Selenka), the maximum rate of food consumption in terms of energy (C_maxe; J day⁻¹) and the specific growth rate in terms of energy (SGRe; % day⁻¹) in animals of three body sizes (mean±SE) – large (134.0±3.5 g), medium (73.6±2.2 g) and small (36.5±1.2 g) – were determined at water temperatures of 10, 15, 20, 25 and 30°C. Maximum rate of food consumption in terms of energy increased and SGRe decreased with increasing body weight at 10, 15 and 20°C. This trend, however, was not apparent at 25 and 30°C, which could be influenced by aestivation. High water temperatures (above 20°C) were disadvantageous to feeding and growth of this animal; SGRe of A. japonicus during aestivation was negative. The optimum temperatures for food consumption and for growth were similar and were between 14 and 15°C, and body size seemed to have a slight effect on the optimal temperature for food consumption or growth. Because aestivation of A. japonicus was temperature dependent, the present paper also documented the threshold temperatures to aestivation as indicated by feeding cessation. Deduced from daily food consumption of individuals, the threshold temperature to aestivation for large and medium animals (73.3–139.3 g) was 24.5−25.5°C, while that for small animals (28.9–40.7 g) was between 25.5 and 30.5°C. These values are higher than previous reports; differences in sign of aestivation, experimental condition and dwelling district of test animals could be the reasons.

The sea cucumber Apostichopus japonicus is exploited as a commercial species owing to their high nutritive and medicinal value. Recent high summer temperatures have caused high mortality rates in A. japonicus. In this study, we applied the isobaric tag for relative and absolute quantitation (iTRAQ) technique to investigate the global protein expression profile under an acute short-term (48 h) heat stress. In total, 3432 proteins were identified, and 127 proteins showed significant heat stress responses, with 61 upregulated proteins and 66 downregulated proteins. Our results suggest that heat stress influenced the expression of proteins involved in various biological processes, such as tissue protection and detoxification, lipid and amino acid metabolism, energy production and usage, transcription and translation, cell apoptosis, and cell proliferation. These findings provide a better understanding about the response and thermo-tolerance mechanisms of A. japonicus under heat stress.