Hirotaka Kakita1, Naoki Yanaoka1, Hideki Obika2
1Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, 156-8550, Japan
2Health Research Institute, National Institute of Advanced Industrial Science and Technology, Kagawa, 761-0301, Japan
Nutrient loading from fish aquacultures is one of the major aquatic environmental degradation, although fish aquaculture is important for food sources. High concentrations of nutrients often promote phytoplankton blooms. Harmful phytoplankton releases large amounts of shellfish toxins. Any effective solutions to the environmental problem are now requested. On the other hand, marine macro alga uptakes a large amount of dissolved nutrients such as nitrogen and phosphorous during algal growth. Thus, macro alga is one of the candidates that can be used to reduce dissolved nitrogen and phosphorus in fish wastewater. The aim of this study was to evaluate the uptake of ammonium nitrogen in fish wastewater by Japanese algal family Gracilariaceae. The time course of nutrient loading from fish into seawater after feeding was investigated under various conditions. Fifteen kinds of unialgal culture strains of the Japanese algal family Gracilariaceae were surveyed for ammonium nitrogen uptake. Ammonium nitrogen concentration in seawater was determined by using a continuous flow analyser Model QuAAtro. Among Japanese Gracilariaceae tested, Gracilariopsis chorda strains had a large intake of ammonium nitrogen. A G. chorda biofilter with algal density of 1 g / L reduces ammonium nitrogen below the Japan standard value (dissolved nitrogen 1.00 mg / L) in 24 hours. Gracilariopsis chorda is one of the industrially important macro algae in Japan, it can be used for foods and food additives such as agar after nutrient uptake. Thus, Gracilaria chorda seem to be suitable alga as a biofilter.