Food intake and digestion in the scavenging lysianassid gammaridean Scopelocheirus onagawae

The lysianassid gammarid Scopelocheirus onagawae, which inhabits temperate shallow waters, was investigated for its digestion time and amount of food intake in feeding experiments with fish paste containing food dye as bait, being compared to those of cold-water species. The specimens were collected in Onagawa Bay, north-eastern Japan, from May through November 2001, using baited traps. The experiment on digestion time was run at 8°C, and the experiment on amount of food intake at 6, 8, 13, 18 and 21°C. Each individual that was fed fish paste was crushed in 3% ammoniaethanol solution to extract the food dye. After centrifuging, the fluorescence intensity of the supernatant was measured and converted to food intake. Individuals of 0-h non-feeding showed the relative food intake of approximately 1.0%, and those of 24-h non-feeding showed the value of 4.3%. Based on the finding that the satiation ratio ranged from 3.6 to 4.1% for all feeding individuals, this species were considered to digest food completely within 24 h. The satiation ratios were much less than those of cold-water species. Several tens of thousands of S. onagawae were inferred to congregate on carcasses and consume it in a short period after sunset.