Occurrence periods and food habits of cresthead flounder Pleuronectes schrenki Juveniles in Lake Notoro, Hokkaido [Japan]
1999
Takatsu, T. (Hokkaido Univ., Hakodate (Japan). Faculty of Fisheries) | Takagi, S. | Yokoyama, S. | Takahashi, T.
To elucidate the occurrence periods, the food habits and somatic growth conditions of cresthead flounder Pleuronectes schrenki juveniles, sampling was conducted with an epibenthic sledge net for juveniles and with a Van Dorn bottle for their food organisms in Lake Notoro in June-July 1992 and May-August 1993. Lake Notoro is a subarctic, brackish lake that opens into the Sea of Okhotsk. Juveniles were found in nearshore areas (1.0-6.0 m depth) in July 1992, June, July and August 1993, but not in June 1992 or May 1993. Almost all juveniles were distributed in areas with sandy bottom or sandy bottom with scattered seaweed beds. Juveniles fed mainly on Eurytemora spp. in July 1992 and August 1993, and harpacticoid copepods other than Microsetella spp. in July 1993. Large food organisms, such as gastropods, polychaetes, mysids, cumaceans, gammarids and caprellids, were subsidiary prey for juveniles and composed a small portion of the stomach contents. Eurytemora spp. and harpacticoids other than Microsetella spp. were smaller (0.23-0.33 mm width and 0.08-0.28 mm width, respectively) than the other food organisms, and were distributed near the lake bottom during daylight. These coastal and demersal copepods could sustain the growth of cresthead flounder juveniles in Lake Notoro at their nursery ground. Two allometric growth curves between standard length and body weight indicated that juveniles were significantly heavier in July 1992 than in July 1993. It is possible that Eurytemora spp. are a more effective food source for juvenile somatic growth than demersal harpacticoids in July
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