Effects of dietary inclusion of benthic matter on feed utilization, digestive and immune enzyme activities of sea cucumber Apostichopus japonicus (Selenka)

A 70-day feeding experiment was conducted to examine the effects of dietary inclusion of benthic matter, which was mainly composed of microalgae, bacteria and clay particles, on the feed utilization, digestive and immune enzyme activities of sea cucumber Apostichopus japonicus. Sea cucumbers were fed with 6 types of diets with the ingredient of either single algae species or mixture of algae and benthic matter, i.e., single brown alga Sargassum muticum, red alga Gracilaria lemaneiformis, green alga Ulva lactuca, mixtures (1:1) of S. muticum and benthic matter, G. lemaneiformis and benthic matter and U. lactuca and benthic matter. After the feeding trial, the feed utilization efficiency, digestive and immune enzyme activities of A. japonicus were remarkably affected by different types of diets. The feed conversion ratio of A. japonicus fed the single G. lemaneiformis was significantly higher than those fed with single S. muticum and those fed on G. lemaneiformis with benthic matter (ANOVA, p<0.05). While the protein efficiency ratios of A. japonicus fed the single algae diets were significantly lower relative to those fed on corresponding mixed diets (ANOVA, p<0.05). The trypsin activity of A. japonicus that fed the single G. lemaneiformis was not only significantly lower than those fed the single S. muticum and single U. lactuca but also significantly lower than those fed on G. lemaneiformis with benthic matter (ANOVA, p<0.05). The amylase and cellulase activities of A. japonicus that fed the single algae diets were significantly lower as compared to the corresponding mixed diet groups (ANOVA, p<0.05). Similarly, the superoxide dismutase and acid phosphatase activities of A. japonicus that fed the single algae diets were significantly lower relative to those fed on corresponding mixed diets (ANOVA, p<0.05). While the alkaline phosphatase activity of A. japonicus fed on G. lemaneiformis with benthic matter was not only significantly higher than those fed the G. lemaneiformis alone but also significantly higher than those fed on S. muticum with benthic matter and U. lactuca with benthic matter (ANOVA, p<0.05). The results of the present study suggested that dietary inclusion of benthic matter might have beneficial effects on the digestive processes, immune responses and growth performance of A. japonicus.The results of the present study can provide the scientific suggestions for optimizing the feed ingredients for farming of sea cucumber A. japonicus.