DIETARY EFFECTS OF THREE SMALL ALGAL SPECIES ON GROWTH OF THE SEA URCHIN Mesocentrotus nudus JUVENILES

The sea urchin Mesocentrotus nudus juveniles, which are densely found on barrens, would be the potential stock for sea urchin aquaculture. To develop a diet that promotes sea urchin growth, this study confirms the dietary effect of three small algal species: frozen or dried Gloiopeltis furcata (FG, DG), frozen or dried Mazzaella japonica (FM, DM) and frozen Scytosiphon lomentaria (FS), on the growth of M. nudus juveniles compared with the juveniles fed the kelp Saccharina japonica and the starved juveniles.

We conducted the feeding experiment during October-December in 2017. The crude protein content of G. furcata was 16.2%, highest among the three algal species. The food intake of FG and DG were more than those of the other algae except for kelp. The food conversion efficiencies (body weight gain × 100/ food intake) and growth rates of FG and DG were significantly higher than those of other algae (FIGURE 1). The gonad index of the urchins fed DG was significantly higher than those fed other algae. These results indicate that high crude protein content of G. furcata and its high food conversion efficiency and food intake (FG and DG) promoted the somatic growth of M. nudus juvenile. The high gonad production of DG may be due to allocation of surplus protein derived by heating in the drying process to gonad.