Life history characteristics of the fluvial shrimp Macrobrachium yui (Holthuis, 1950) (Decapoda, Palaemonidae) spawning in the cave streams in northern Laos

Abstract

This study aims to understand the reproductive and larval characteristics and the migratory patterns of the shrimpMacrobrachium yui(Holthuis, 1950). We conducted monthly samplings of the adult, juvenile and larval shrimp at fixed points in the Xuang River system in northern Laos. We determined the seasonal changes in size frequency distribution, difference in size among sampling sites, occurrence of drifting larvae, and physiological condition of the shrimp. The size distributions ofM. yuidiffered significantly throughout the year among sections of the river system: small-sized juveniles occurred in the Xuang River, various size classes in the Pho Stream, and larger adults in the Bokengsakang cave stream. The gonadosomatic index of females is the highest in the Bokengsakang cave stream and the gonadosomatic index of males is the highest in the Pho Stream. Drifting larvae that had already completed morphological development for settlement on the substrate occurred only in the Bokengsakang cave stream, although the hatched larvae have a free-swimming larval period. The overall results indicate thatM. yuifemales spawn in the Bokengsakang cave stream after mating with males during or before migration to the cave stream, and the hatched larvae remain in the cave stream until settling on the bottom. The life history migration ofM. yuiis attributed to the early stages of the life cycle, depending strongly on the cave stream.