University of Miyazaki, Japan
Dr. Taoka has completed his PhD at the age of 28 years from the United Graduate School of Agricultural Sciences, Kagoshima University and postdoctoral studies from University of Miyazaki. He worked in a commercial fisheries company, Nippon Suisan Kaisha, Ltd. as a researcher and arrived at present post in University of Miyazaki at 2011. Recently, he has focused on the production of functional substances from marine microbes and the utilization in the field of aquaculture.
World aquaculture production has continued to increase. Fishmeal is used as protein sources for aqua-feeds. However, the price is drastically increased to around 170,000/ ton in 2013 during recent 10 years because of the decrease of fish resources, anchovy. This is serious problem for sustainable aquaculture. Therefore replacement of fishmeal to another resource is urgently needed. Several researchers reported the replacement of protein sources from fishmeal to plants. However, the complete replacement by plant proteins are not established yet because plant sources contained some components that negatively affect the growth of the cultured fish due to the low digestibility. We focused on the “thraustochyrids” as probiotics to enhance the digestibility of plant sources.
Thraustochytrids are widely distributed in marine environment and have unique characteristics that accumulate large amount of lipids in cell bodies. Additionally, it is known that thrastochytrids produce various extracellualr enzymes including refractory components such as cellulose.
In this study, we researched the profile of extracellular enzymes from thraustochytrids and the tolerant ability in the gastrointestinal juices in vitro and in vivo to evaluate the potency as probiotics. Production of various extracellular enzymes, protease, amylase, lipase (tween 80 hydrolytic enzyme), cellulase and tannase were detected depending on the genus or species of thraustochytrids. The tolerance to artificial gastric juices was high in genus Aurantiochytrium and Ulkenia, and low in genus Oblongichytrium. In the case of in vivo test, Aurantiochytrim was recovered from the intestine of Japanese short-necked clam, Ruditapes philippinarum (“Asari” in Japanese). Additionally, we have isolated more than one hundred thraustochytrids from marine environment and are screening probiotic abilities to select adequate strain now. As next step, we are planning the rearing trial with aquaculture-major fish species and supply live thrautochytrids by oral administration