Using carbon stable isotope ratio(δ~(13)C)to evaluate contribution of artificial feeds to growth of pond cultured juvenile sea cucumber Apostichopus japonicus(Selenka)

Sea cucumber Apostichopus japonicus(Selenka)is a typical deposit-feeder,that is,food came from some organic matter in sediment such as bacteria,prozotoa,benthic microalgae and detritus of macroalgae.Artificial feeds are applied in some areas for sea cucumber farming to increase production of the pond cultured sea cucumbers,however,to what extent the artificial feed contributes to their growth is still unclear.Study on the food sources by a traditional way of direct gut content analysis has limitations.Stable isotope is a predictable method to evaluate food sources of A.japonicus.The present experiments were conducted to estimate contribution of artificial feed to growth of sea cucumber at five different stocking densities(5,10,15,25 and 35 ind/m2)using a stable carbon isotope ratio(δ13C)tracer.Sea cucumbers with an average weight of(4.78±0.58)g were randomly assigned to the enclosures.The animals were fed with artificial feed at 8:00 every day,at a feeding rate of about 5% wet weight.There were 5 treatments and 3 replicates in the experiment that lasted for 6 months.The control treatments without feed were set simultaneously.A lab experiment with four plastic aquaria(100 cm×60 cm×60 cm)was conducted and feeding time and ration were the same as the pond experiment.The results showed that the final weight and δ13C value of sea cucumbers were affected markedly by both artificial feed and stocking density(P0.05).With stocking density increasing,final weight of the animals decreased from(35.62±3.50)g to(24.59±4.38)g,and with stocking density increasing from 5 ind/m2 to 35 ind/m2,the δ13C values of sea cucumbers decreased from-13.262‰ to-15.102‰(P0.05).Contributions of artificial feed to the growth of the sea cucumbers increased with increasing of stocking density,only 3.78%±2.98% at 5 ind/m2 to 29.48%±3.31% at 35 ind/m2.Previous studies showed that artificial feed contributed 23.0%-61.6% to the growth of shrimp and fish,which is higher than that to A.japonicus.This was caused by quality of artificial feed and the physiological characteristics of feeding behavior of sea cucumbers.