|The feeding activities of Yellowtail larvae, Seriola quinqueradiata Temminck et Schlegel, associated with floating seaweeds|
Anraku, M.; Azeta, M. (1967). The feeding activities of Yellowtail larvae, Seriola quinqueradiata Temminck et Schlegel, associated with floating seaweeds. Bull. Seikai Natl. Fish. Res. Inst. 35: 41-50
In: Seikai-ku Suisan Kenkyujo kenkyu hokoku = Bulletin of the Seikai National Fisheries Research Institute. Seikai Regional Fisheries Research Laboratory: Nagasaki. ISSN 0582-415X, more
Feeding behaviour; Floating; Larvae; Seriola quinqueradiata Temminck & Schlegel, 1845 [WoRMS]; Marine
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In the preceding report the authors have investigated the feeding habits of larvae and juveniles of the yellowtail, Seriola quinqueradiata, associated with floating seaweeds. The collections of specimens used in the previous work were only limited to the daytime. To proceed the further analysis of the feeding habits, the activities at night should thus be observed simultaneously with those in the daytime. In June 1964 and 1965, we have had the opportunity to pursue a group of floating seaweeds in the Iki Channel, northern Kyu-shu, Japan, to make a series of yellowtail larvae samplings. In a twenty-four hour period, the operations of small purse seine were repeated with a certain time interval. Fifty individual yellowtail larvae of each collection were used for the examination of the stomach contents. The samplings of planktonic foods in the surrounding water were made by a series of surface net tows and pumpings. Ten species of fish were identified from the floating seaweeds (Table 1). The yellowtails occurred in every collection and their numbers reached up to 91-98% of the total number of specimens. Their size frequencies are shown in Fig.2. The night collections confirmed that the larvae of S. quinqueradiata were swimming around floating seaweeds even at night as they do in the daytime. Same as in previous findings, fish larvae, almost all northern anchovy, and crustacean plankton, mostly copepods, were the main source of foods, The change of the composition of important food organisms (Table 2) revealed that copepods were eaten in every group of yellowtail except one regardless of the time of day. The percentage occurrence of larger copepods eaten was higher in the night populations than that of the daytime. The larger crustaceans such as brachyuran zoea, macruran mysis, Euphausia and Lucifer were eaten mainly before and after sunrise as well as sunset. The ratios of individuals eating fish to total individuals were found high in the early morning and in the evening. While, those were quite low during midday and at midnight. The changes of the feeding rate of each group. with the sampling time of the day, indicated that the values for the group captured before and after sunrise as well as at sunset were greater than those for the larvae collected in the daytime and at night (Fig. 3). The feeding rates of each group obtained for every 10 mm of the total length of larvae also show active feeding around sunrise and sunset (Fig. 4). The distribution of crustacean plankton in the surface layer where the yellowtail larvae were feeding showed a considerable diurnal variation, The amounts of planktonic food were thus scarce during daytime and abundant at night (Fig. 5), The quantity of larval fishes, the other important source of food, in the layer just below the sea surface may fluctuate in the same manner as zooplankton. The combined results of the present investigation suggest that the yellowtail larvae associated with floating seaweeds eat very little at night. They start to feed actively a little before sunrise, and this condition continues until some time after it. In general, the activity seems to become low in the daytime. They then eat vigorously in the evening before and after sunset.