EFFECTS OF SEAWATER TEMPERATURE ON SCALE CIRCULI DEPOSITION OF REAREDRED-SEA BREAM

Scale circuli of juvenile red sea bream Pagrus major were counted to i nvestigate the relation between circuli deposition and seawater temper ature. The samples were collected from three experimental stations; Mo moshima: MS and Hakatajima: HT in the western Seto Inland Sea and Miya zu: MZ on the western coast of the Sea of Japan. The larvae which were collected from the same parents group in HT were distributed into MS and HT and reared until they grew to juveniles in each place. The samp les in MZ were reared in Miyazu from larvae to juveniles and their par ents were different from those in MS and HT. The thermal condition and size of rearing tanks were different among the three stations. Temper atures in the three stations showed characteristic fluctuations. Mean temperatures in the experimental periods were calculated as follows; M S: 26.5-degrees-C, HT: 21.7-degrees-C and MZ: 22.7-degrees-C. The dail y deposition rate seemed to depend on their scale growth rate in accor dance with their body growth since the circuli numbers were linearly p roportional to their fork length. The circuli numbers per fork length were in proportion to the mean temperature; MS: 1.35 numbers/mm, 26.5- degrees-C, HT: 1.28 numbers/mm, 21.7-degrees-C and MZ: 1.27 numbers/mm , 22.7-degrees-C. Number of days until first-circulus deposition was i nversely proportional to the mean temperature: MS: 19 days, HT: 44 day s and MZ: 48 days. These results indicated that seawater temperature a ffected the fish growth, therefore affecting the circuli deposition an d that the thermal condition in the different sea-farming stations was written into juvenile fish scales.