Higher dietary protein increases growth performance, anti-oxidative enzymes activity and transcription of heat shock protein 70 in the juvenile sea urchin (Strongylocentrotus intermedius) under a heat stress

This study was conducted to investigate the effect of dietary protein concentration (12%, 18%, 24%, 30% and 36%) on the growth performance, activity of anti-oxidative enzymes and heat shock protein 70 (HSP70) transcription in the sea urchin (Strongylocentrotus intermedius) under a heat stress. After 112 days of feeding trial the sea urchins were heat stressed (26 °C) and the coelomic fluid and intestine sampled at time 0 and 15 min, 2 h and 6 h. The results showed that an increase in dietary protein (12%-24%), significantly increased (p < 0.05) the sea urchin weight gain rate (WGR). As dietary protein increased (from 18% to 36%), the gonadosomatic index (GI) of juvenile sea urchins also significantly increased (p < 0.05) from 18.0% to 22.6%. Superoxide dismutase (SOD) activity increased with dietary protein increase (12%-30%) and the enzyme activity was significantly higher (p < 0.05) in the coelomic fluid of sea urchins that were fed with 30% protein diets when compared to 12% and 36% protein diets at all time points after the heat stress. Catalase (CAT) activity showed a similar tendency with the increase in dietary protein concentration at time 0 and 15 min after the heat stress (p < 0.05). Transcription of HSP70 in the intestine also showed a similar trend to SOD and was highest in the animals that were fed with 30% protein diets (p < 0.05). Our results suggest that 24% protein diets could meet the requirements for growth performance but a 30% protein diet resulted in improved gonad development and anti-heat stress capacity in this sea urchin species.