Utilization of corn meal and extruded soybean meal by sea cucumber Apostichopus japonicus (Selenka): Insights from carbon stable isotope analysis

Feed utilization of sea cucumber Apostichopus japonicus (Selenka) fed diets with different proportions of terrestrial plants, including corn meal and extruded soybean meal, as the substitutes of brown algae Sargassum thunbergii was determined by means of carbon stable isotope analysis. Carbon stable isotope ratios (δ13C) of the different ingredients in diets and the isotopic shifts of sea cucumber fed different diets were determined. The different δ13C values of the various ingredients and the changing ratios of the different ingredients in the formulated diets resulted in the distinguishable isotopic signal between different diet types, and the shifts in the δ13C values of sea cucumber in different groups showed a tendency to approach the δ13C values of corresponding diets. Replacement of S. thunbergii by the mixture of corn meal and extruded soybean meal in formulated diets with suitable proportion might promote the growth of sea cucumber owing to the relatively higher utilization efficiency of corn meal and extruded soybean meal compared to S. thunbergii. However, further replacement of S. thunbergii by the mixture of corn meal and extruded meal in diets resulted in the decreased utilization efficiency of corn meal and extruded soybean meal by sea cucumber and the subsequent reduction in the growth performance of sea cucumber.