The olfactory hypothesis for salmon imprinting and homing to their natal stream is well known, but the endocrine hormonal control mechanisms of olfactory memory formation in juveniles and retrieval in adults remain unclear. In brains of hatchery-reared underyearling juvenile chum salmon (Oncorhynchus keta), thyrotropin-releasing hormone gene expression increased immediately after release from a hatchery into the natal stream, and the expression of the essential NR1 subunit of the N-methyl-D-aspartate receptor increased during downstream migration. Gene expression of salmon gonadotropin-releasing hormone (sGnRH) and NR1 increased in the adult chum salmon brain during homing from the Bering Sea to the natal hatchery. Thyroid hormone treatment in juveniles enhanced NR1 gene activation, and GnRHa treatment in adults improved stream odour discrimination. Olfactory memory formation during juvenile downstream migration and retrieval during adult homing migration of chum salmon might be controlled by endocrine hormones and could be clarified using NR1 as a molecular marker.

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The concentrations of 228Ra and 226Ra in the surface and subsurface sea water samples collected from the East Indian and the West Pacific Ocean were determined. Radium isotopes were analyzed by -1-ray spectrometry or 228Th milking method . Surface waters of the northern Indian Ocean to the north of latitude 30°S contained higher concentrations of 228Ra (63-32dpm/1,0002) than those of southern area and the West Pacific Ocean (less than 8dpm/1,0002). The samples from near shore water of Indonesia and the South China Sea showed high 228Ra contents, 629-164dpm/1,000Q.The con centrations of 228Ra in subsurface waters were very low except for the South China Sea. A major source of 228Ra in the Indian Ocean may be coastal sediments of Indonesia. The mixing rate of surface water masses across the subtropical convergence was calculated by using a simple box model to be about 41 km/y.

Abstract-The concentrations of radium isotopes (22.Ra and 228Ra) and thorium isotopes (232Th, 230Th and 228Th) in a calcium carbonate sinter cone and hokutolites were determined. These nuclides were analyzed either by non-destructive y-ray spectrometry or by a-ray sepc trometry after radiochemical separation. The concentrations of 232Th, 228Ra and 228Th (thorium series nuclides) in a sinter cone were 2.4 X 10-2, 4.3 X 10-1 and 7.1 X 10-1 dpm/g, respectively. It was confirmed that thorium series nuclides in this sample were not in radio active equilibrium with their parent, 232Th. Hokutolite samples collected recently showed higher radioactivities of 228Ra, ranging from 9.6 X 104 to 2.8 X 104dpm/g BaSO4. These values give a rate of deposition and an initial composition of the radionuclides in the hokutolite.

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