ネズッポ属(Callionymus)魚類の食性について : I. ネズミゴチCallionymus punctatus LANGSDORFFの食性

ネズミゴチの食性を明らかにするために,瀬戸内海中部の小型底曳網漁獲物の中から採集したネズミゴチ46個体の消化管内容物を調査し,さらに瀬戸内海中部の仙酔島の砂場および藻場のベントスとそこで採集した23個体のネズミゴチの消化管内容物をそれぞれ調査して次のような結果を得た。
1) ネズミゴチの餌生物は甲殻類のCumacea, Ostracoda, カニ類, Amphipoda, Copepoda,エビ類, Anomura, オキアミ類, Branchiopoda, Mycidaceaと巻貝,二枚貝および多毛類であるが,調査したネズミゴチの半数以上の個体に捕食されていたCumacea, Ostracodaおよび巻貝が重要な餌生物である。
2) ネズミゴチの成魚の餌生物組成は雌雄の間で差異がなく,また体長110～129mmと130～164mmとの間についても差異がない。
3) 仙酔島の砂場のベントスの組成と藻場のベントスの組成とは著しく相違しているのに対し,砂場と藻場の両者において,それぞれのベントスとそこで採集したネズミゴチの消化管内容物の組成は極めてよく類似していた。すなわち個体数において,砂場ではウミホタルが卓越してベントスの53%を占め,ネズミゴチの消化管内容物の中では79%を占めた。次いで砂場では貝類が多数出現して,それはベントスの28%を占めたのに対し,消化管内容物では8%を占めた。藻場ではホトトギスガイが卓越してベントスの87%を占め,消化管内容物の中では59%を占めた。
4) 藻場に生息していたネズミゴチの消化管内容物の59%を占め,ネズミゴチの最も重要な餌生物の一つであるホトトギスガイは仙酔島の藻場に比較的多く出現したアサヒアナハゼ,クジメおよびアイナメには殆んど捕食されていなかった。しかし藻場のネズミゴチに殆んど捕食されていないGammarideaはこれら3種の魚類によってしばしば捕食されており,それらの最も重要な餌生物であることがわかった。したがってネズミゴチは藻場ではアサヒアナハゼ,クジメおよびアイナメと食物について競合関係がない。

The dragonets, genus Callionymus, is very common and found frequently with other demersal fish in the catch of a small trawl in the Seto Inland Sea. In this study, the food habits of "Nezumigochi", Callionymus punctatus LANGSDORFF, have been investigated through analysis of their gut contents and benthos of their habitat, Sensui-shima in the central region of the Seto Inland Sea (Fig. 1). The material of 46 individuals were caught by a small trawl net. They ranged from 110 mm to 163 mm in standard length (Fig. 2). To compair the diet of this fish with the benthos of their habitat, 14 individuals in the sand area and 9 individuals in the Zostra zone were sampled by spear, the benthos of the area were also sampled by quardrat method (Fig. 4 ).

The general conclusions reached in this study are as follows:
1) The food organisms occurred in the guts were crustacea, bivalvia, gastropod a, and poly-chaeta. The crustacea contained the following organisms: branchiopoda, ostracoda, copepoda, mysidacea, cumacea, amphipoda, euphausiacea, macurura, anomura, brachyuran and stomatopoda. The main food organisms were cumacea for 72 % of the 46 stomachs, gastropoda for 65 %and ostracoda for 61 %. On the contrary, euphausiacea, macurura and anomura seemed to be preied on only occasionally, and branchiopoda, mysidacea and stomatopoda still more rarely (Table 1).
2) The difference between the diet of the male and female adult could not be statistically determined (Fig. 3). The diets of the specimens of 110-129mm and those of 130-164 mm were very similar.
3) The benthos of the sand area and that of the Zostera zone were clearly different in composition. Namely, in the benthos of the sand area Cypridina hilgendorfii (ostracoda) occupied 53%, but in the benthos of the Zostera zone Musculus (Musculista) senhousia (bivalvia) 87%. The composition of the food organisms and benthos sampled in each habitat were very similar to each other (Table 3). In the sand area, Cypridina hilgendorfii occupied 53% of the benthos but 79% in the food organisms. In the Zostera zone, Musculus (Musculista) senhousia occupied 87% of the benthos, but 59% in the food organisms (Table 2).
4) Musculus (Musculista) senhousia, the main food organisms of C. punctatus in the Zostera zone, were rarely taken in by the common inhabitant of the Zostera zone around Sensui-shima: Pseudoblennius cottoides, Agrammus agrammus and Hexagrammos otakii. But gammaridae that occupied only 6% in the food organisms of C. punctatus in the Zostera zone were often eaten by these 3 species mentioned above (Fig. 5). Accordingly, it is considered that C. punctatus is not in competition with these 3 species for prey.