A euphausiid, Euphausia pacifica, as an important food source to demersal fishes in the eastern Korean water

Abstract

Large amount of euphausiids, Euphausia pacifica, is found to be distributed in the eastern Korean water adjacent to Uljin, which often form near-bottom aggregation in the depth of 100-200m approximately (in preparation). During the studies on euphausiids, we examined gut contents of several species of fishes to partially understand their ecological roles. Among the fishes caught in fishery nets set close to the region where euphausiids aggregations were observed, only two fish species, arabesque greenling (Pleurogrammus azonus) and spinyhead sculpin (Dasycottus steiger) were available with sufficient amounts for data in the collection of Oct 2002 (only in D. steiger), Mar 2003 and Jun 2003, while other species captured with small amounts also often included euphausiids in their guts. Euphausiids were significantly important food source to the species of fishes examined. All of the stomachs of arabesque greenling examined contained euphausiids (% of a food item frequency, F = 100 %) in Mar and Jun 2003. Individual numbers of euphusiids in the guts ranged from 10 to 540 ind / gut. Squids were simply the alternative food item found in arabesque greenling (% of number of food item, Cn = 99.96 for euphausiids). The fish showed great preference to euphausiids, even though they can feed on much larger squids. On the other hand, they preferred to larger euphausiids which size range was 17.2 - 28.4 mm, while the size range of euphausiids distributed in the ambient water column was much broader (from eggs to adults). The guts of spinyhead sculpin also frequently contained euphausiids (F = 79.20 %), while amphipods (F = 16.17 %) and other fishes (F = 45.80 %) were also often observed. In terms of number of individuals, euphausiids, as a small sized animals among the food item, were the most frequently chosen prey (Cn = 99.49 %).