魚類稚仔期の口径に関する研究-II

Abstract

Studies on the mouth size of larval fishes have not yet been fully made. The author measured the mouth size of various larval fishes which had absorbed yolk and just begin to take natural live food, and studied the relationship among mouth size, food size and growth of fish. Total body length of the material fishes ranged from 10 to 20mm. The results obtained are as follows. 1. No definite relationship was found between the mouth size and the total body length at the time of commencement of feeding. 2. The mouth size of various larval fishes at the time of commencement of feeding ranged from 200 μ to 1.000 μ and was observed to have a close relationship to the size of their natural foods: That is, larval fishes having small mouth sizes, such as Hypomesus, Plecoglossus, Ammodytes, Sillago, Konosirus and Oplegnathus take only phytoplankton, protozoa and the nauplii of small copepods, but larval fishes having big mouth sizes, such as Thunnus, Katsuwonus, Seriola, Girella, Mugil, Lateolabrax and Clupea were found to easily take large copepods at the time of commencement of feeding. 3. Although the body size at the time of commencement of feeding, in fishes of rapid growth such as Thunnus, Katsuwonus, Seriola and Scomber, was much smaller (about 1/2) than that of Clupea, their mouth size was equal to or larger than that of Clupea. 4. It was made clear that the quicker the growth of fish, the greater is the mouth size at the time of commencement of feeding.