Effects of Seawater Temperature on Scale Circuli Deposition of Reared Red Sea Bream

Abstract

Scale circuli of juvenile red sea bream Pagrus major were counted to investigate the relation between circuli deposition and seawater temperature. The samples were collected from three experimental stations; Momoshima: MS and Hakatajima: HT in the western Seto Inland Sea and Miyazu: 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 samples in MZ were reared in Miyazu from larvae to juveniles and their parents were different from those in MS and HT. The thermal condition and size of rearing tanks were different among the three stations. Temperatures in the three stations showed characteristic fluctuations. Mean temperatures in the experimental periods were calculated as follows; MS: 26.5°C, HT: 21.7°C and MZ: 22.7°C. The daily deposition rate seemed to depend on their scale growth rate in accordance with their body growth since the circuli numbers were linearly proportional to their fork length. The circuli numbers per fork length were in proportion to the mean temperature; MS: 1.35 numbers/ mm, 26.5°C, HT: 1.28 numbers/mm, 21.7°C and MZ: 1.27 numbers/mm, 22.7°C. Number of days until first-circulus deposition was inversely proportional to the mean temperature: MS: 19 days, HT: 44 days and MZ: 48 days. These results indicated that seawater temperature affected the fish growth, therefore affecting the circuli deposition and that the thermal condtion in the different sea-farming stations was written into juvenile fish scales. © 1995, The Japanese Society of Fisheries Science. All rights reserved.