COMPARISON OF GROWTH PATTERN UNTIL SEXUAL MATURITY BETWEEN THE ESTUARINE AND UPPER FRESHWATER POPULATIONS OF THE PRAWN MACROBRACHIUM NIPPONENSE (DE HAAN) WITHIN A RIVER

Abstract

The growth of individuals until sexual maturity in the prawn Macrobrachium nipponense was comparatively investigated between the estuarine and upper freshwater populations of a river. The growth of upper freshwater individuals was noticeably depressed, but most of the females seemed to spawn at one year of age like the estuarine females at nearly the same breeding season. The males were presumed to participate in spawnings at two or more years of age at both sites. The undelayed oviposition in the upper freshwaters despite their depressed growth was considered to be due to their maturity at small body size. The relatively early maturity to size is supposed to be a specific life history trait of the upper freshwater population.