Culture of benthic diatom Nitzschia sp. with macroalgae carriers and its application as feed of juveniles Stichopus japonicus

Carrier culture is the combination of suspension culture and adherent culture. Carriers could be used to improve the culture efficiency of large-scale culture of adherent benthic diatom. In order to identify a suitable carrier for mass suspension culture of the benthic diatoms Nitzschia sp. powders of seven macroalgae were used as carriers for diatom attachment including Ulva pertusa, degummed Laminaria japonica, Sargassum muticum, Chaetomorpha valida, Zostera marina, Sargassum fusiforme and Sargassum thunbergii. Diatoms could grow on the surface of the suspended carriers and could effectively utilize the nutrients released by the decomposition of these carriers. Among the seven carriers, Ulva pertusa powder was the most effective for Nitzschia culture when comprehensively considering the nutrition of the harvested diatoms and nutrient utilization of the algae carrier by diatoms. The seaweed powder was dried at 80 °C before used as carrier, this process should meet the sterilization requirements for microalgal culture and is easy to implement in the large-scale cultivation of diatoms. Diatoms cultured with carriers were used to feed juveniles Stichopus japonicus with a wet weight of 5.0 ± 2.0 g, as well as diatoms cultured using conventional methods without carriers, and no significant differences were observed between the two kinds of feed. Compared to sea cucumbers fed with commercial feed, the growth rate of S. japonicus fed with carrier-cultured diatoms was approximately 1.5 times greater, and the activities of non-specific immune enzymes were improved in the coelomic fluid including acidic phosphatase, alkaline phosphatase and superoxide dismutase. Feeding sea cucumber with fresh diatoms could effectively reduce the total nitrogen and total phosphorus in the culture water, improve the water quality, and promote the breeding of sea cucumbers, regardless of whether the carrier culture was adopted.