ALLOCATION OF DIGESTED MATERIALS TO MAIN BODY COMPARTMENTS OF THE SEA URCHINS Mesocentrotus nudus AND Hemicentrotus pulcherrimus  

For exploitation of the potential stock of Mesocentrotus nudus on barren habitats and Hemicentrotus pulcherrimus that is not commercially harvested in northern Japan, short-term feeding culture to enhance gonad production will be desirable. To determine the most optimum season for the culture, this study aims to clarify the seasonal and species-specific allocations of digested dry matter, carbon (C) and nitrogen (N) to major body compartments of M. nudus and H. pulcherrimus fed a formulated diet.

We conducted the four-week feeding trials four times during June-July and October-November in 2012, and January-February and April-May in 2013. We weighed four main body compartments (test, lantern, gut, gonad, dry), and analyzed C and N contents at the start and end of the feeding trials. We calculated apparent allocation rate (%) (dry matter, C or N gain of each main body compartments × 100/ dry matter, C or N digested). Digestibility of C and N (C or N digested × 100/ C or N intake) of the feed by H. pulcherrimus was significantly higher than those by M. nudus except for the trial during January-February. For M. nudus, the N apparent allocation rates to gonad were high during June-July, January-February and April-May, although the rate to test was also high during January-February. This suggests that feeding after February would be efficient to promote the gonad production in M. nudus. For H. pulcherrimus, the apparent allocation rates of dry matter, C and N to gonad were markedly high during June-July. The short-term intensive feeding during this period appears to enhance the gonad production in H. pulcherrimus.