The influence of photoperiod on growth an dreproductive organs of male giant freshwate prawns, Macrobrachium rosenbergii di Man

Abstract

The purpose of this study was to determine the effect of photoperiod on growth and reproductive organs of male giant freshwater prawns, Macrobrachium rosenbergii de Man. The animals, about 8-10 weeks of age with the initial hody weight of 6-7 g, were maintained in the laboratory condition for 22 weeks. They were divided into two groups; one exposed to long-day photoperiod (L16:D8) and the other ot short-day photoperiod (L8:D16). During the experiment, molting of individual prawns was closely monitored and all prawns were individually weighed once every two weeks. At the end of the experiment, the growth rate, molt frequency, molt interval, testis weight, andmicroscopic features of the testis and vas deferens were compared. In addition, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of extraction from the eyestalk optic lobe of the two groups was also compared. The results showed that the growth rate of L16:D8 animals was faster than those of the other. This however, is not significant by statistical analysis. The body weight gain during the 22 week-period was also nonsignificantly higher in the L16:D8 animals. The absolute and relative testis weights of the L16:D8 animals were lower than those of the L8:D16 animals; statistically the relative weights were significantly lower in the L16:D8 animals. As increase in molt frequency, though not statistically significant, was also observed in the L16:D8 animals. The molt interval was significantly lower in the L16:D8 animals. The patterns of SDS-PAGE in both groups were identical and consisted of seven prominent bands of protein. In a separate SDS-PAGE experiment, two additional bands of protein were identified prominently only in the optic lobe, probably represented two peptide hormones. The microscopic features revealed normal spermatogenesis. This study suggests that prolonged light exposure stimulates molting, and probably growth, but inhibits testicular growth in M. rosenbergii; the finding may benefit future aquaculture of this species.