Inhibition of growth in juvenile asari clams Ruditapes philippinarum fed Ulva spp. marine silage

Abstract

The suitability of fermented products of Ulva fronds as diets for juvenile asari clams was tested. Ulva fronds were transformed by fermentation into a single-cell product (Ulva marine silage; UMS) of suitable size for ingestion by the clams. No dietary effect was seen in clams fed UMS alone. Furthermore, combined feeding with UMS and Chaetoceros calcitrans, which is considered a suitable diet for clams, resulted in a reduction in growth. An aqueous suspension of Ulva fronds prepared without fermentation showed inhibitory effects on clam growth, which indicated that the presumed inhibitory component(s) originated from the Ulva fronds. Further feeding tests indicated that the component(s) that inhibited clam growth were water soluble and had a molecular weight of < 1000 Da. An authentic product of glucuronic acid, one of the major components of the water-soluble fraction of UMS, induced inhibitory effects on shell growth. However, further study is necessary to identify the components of Ulva fronds that inhibit growth in the asari clam. The results indicate that the utilization of Ulva fronds as marine silage for the asari clam is problematic because they appear to contain component(s) that inhibit clam growth.