5-Hydroxytryptamine enhances larval development of the giant freshwater prawn, Macrobrachium rosenbergii

The effect of 5-hydroxytryptamine (5-HT) on larval development of the giant freshwater prawn, Macrobrachium rosenbergii, was investigated. Four days after hatching, larvae were exposed to 5, 50 or 100 μg/ml 5-HT in 12 ppt commercial seawater for a period of 2 or more days. Continuous exposure to 50 μg/ml or 100 μg/ml 5-HT over 2 days reduced the survival significantly and all larvae died by 13 days post-hatch (after 9 days of exposure). On the contrary, there was no significant difference in the survival of larvae exposed to various concentration of 5-HT for 2 days compared to that of the control. Exposure to 5-HT for 2 days stimulated growth and developmental rate of the larvae. Furthermore, pigmentation of the exoskeleton was also induced within 1 h of exposure. The larvae exhibited bright-orange color on their eyestalks, cephalothoraxes and abdomens. Exposure to 100 μg/ml 5-HT for 2 days produced the highest growth, developmental rate and the strongest pigmentation. The average body lengths 25 days post-hatch of larvae exposed to 50 μg/ml and 100 μg/ml 5-HT for 2 days were 3.5 ± 0.6 mm and 4.3 ± 0.7 mm, respectively, compared to 2.8 ± 0.4 mm that of the control. Furthermore, the rate of transformation of larvae to postlarvae during 30–40 days post-hatch was significantly higher in those exposed to 50 μg/ml and 100 μg/ml 5-HT compared to that of the control. The present study indicates that brief exposure of early stage larvae to 50–100 μg/ml 5-HT enhances growth, developmental rate and pigmentation of the giant freshwater prawn larvae.