On the Food Habits of the White Croaker Argyrosomus argentatus

イシモチArgyrosomus argentatusの食性

Kakuda Shunpei

Matsumoto Kenji

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

瀬戸内海で1976年2月から'77年6月までの間に採集した8標本・310尾のイシモチについて,空胃であった94尾を除き,体長が20-244mmの216尾の胃内容物を調べ,次の結果を得た。
1) 胃内に出現した生物は魚類,エビ類,端脚類,多毛類,頭足類,枝角類,カニ類,口脚類,等脚類であったが,特に多く出現した魚類とエビ類が最も重要な餌生物である。
2) 胃内容物組成は出現頻度によるとエビ類78%,魚類52%であったが,エビ類ではエビジャコとテッポウエビが特に多く,共に18%を占めた。個体数ではエビ75％(エビジャコ49％,テッポウエビ7％)魚類21％であった。
3) 胃内容物が未消化でその重量を測定することができた113尾のイシモチの重量による胃内容物組成は,魚類65%,エビ類29%(テッポウエビ20%,エビジャコ2%)であった。
4) イシモチの生長に伴う餌生物組成の変化を明らかにするために,216尾のイシモチを体長で20-59;60-99;100-129;130-169;170-244mmの5グループに区分し,各グループ間で胃内容物組成を比較検討した。出現頻度,個体数および重量は共に60-99;100-129;130-169mmの3グループ間ではほぼ類似した組成を示したが,これら3グループと他の2グループとの間には,互いに顕著な差異が認められた.すなわち20-59mmグループではエビジャコが最重要種で,出現頻度で61%,個体数で84%,重量で78%を占めた。60-169mmグループではエビ類と魚類が重要な餌生物であって,出現頻度で魚類50％,エビ類87%(テッポウエビ27%,エビジャコ12％),個体数で魚類34%,エビ類57％(テッポウエビ19%,エビジャコ6%),重量で魚類36%,エビ類53％(テッポウエビ38％,エビジャコ0.7%)を占めた。170-244mmのグループの餌生物は魚類が大部分であって,魚類は出現頻度で91%,個体数で82％,重量で94%を占めた。
5) イシモチは上述のように成長に伴って餌生物の種類をかえながら選択的にこれを捕食しているが,同時に餌生物の大きさに対しても選択的である。すなわち,大きい捕食者ほど同じ種類の餌生物の中ではより大きい個体を捕食しており,餌生物の大きさは全長で最大限,捕食者の体長の約3分の1であった。

The food habits of the white croaker, Argyrosomus argentatus (HOUTTUYN), which is an important resource for fishery in the Seto Inland Sea, were investigated through the qualitative and quantitative analysis of the stomach contents. This study, based on 216 fishes caught in the Seto Inland Sea that had a standard length from 20mm to 244mm, is one of the serial studies on the fishery biology of the white croaker in the Sea.

General conclusions obtained in this study are as follows:
1) Food organisms occurred in the stomach were fish, shrimp, amphipoda, polychaeta, cephalopoda, cladocera, brachyura, stomatopoda and isopoda. But fish and shrimp constituted the main food items.
2) In frequency of occurrence, the main food organisms were fish for 52 percent of the 216 stomachs, 78 percent was shrimp and 17 percent were other organisms. Alpheus sp. and Crangon sp. which were the dominant species in shrimp occupied both 18 percent.
3) By numerical method, 21 percent of food organisms of 216 stomachs was fish, 49 percent Crangon sp., 7 percent Alpheus sp. and 19 percent other shrimp.
4) The 113 stomachs contained a total weight of 154, 836mg of food organisms, of which 65 percent was fish, 20 percent Alpheus sp., 2 percent Crangon sp. and 7 percent other shrimp.
5) The main food organisms of young white croakers above 20mm and under 60mm in standard length were shrimp, and the most common was Crangon sp.. Crangon sp. occupied 61 percent of food organisms in stomachs in frequency of occurrence, 84 percent by numerical method and 78 percent by gravimetric method.
6) The white croaker above 60mm and under 170mm in standard length has preied mainly upon shrimp and fish. In frequency of occurrence, shrimp occupied 87 percent and fish 50 percent. Alpheus sp. was dominant in shrimp and occupied 27 percent in 87 percent. By numerical method, shrimp occupied 57 percent (Alpheus sp. 19%) and fish 34 percent. By gravimetric method, shrimp occupied 53 percent (Alpheus sp. 38%) and fish 36 percent.
7) The main food organisms of the adult above 170mm in standard length were fish. The fish occupied 91 percent of the stomach contents in frequency of occurrence, 82 percent by numerical method and 94 percent by gravimetric method.
8) The length of the prey in the stomach of the white croaker increased as the length of the predator himself increased. The total length of the largest prey in the stomach was about one-third of the standard length of eater himself, generally.

水産業 [ 660 ]

英語

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563

[NAID] 40003288794