Karplus, I., Fish and Aquaculture Research Station, Dor, Israel
Hulata, G., Fish and Aquaculture Research Station, Dor, Israel
Ovadia, D., Fish and Aquaculture Research Station, Dor, Israel
Jaffe, R., Fish and Aquaculture Research Station, Dor, Israel

Sexually mature populations of Macrobrachium rosenbergii are composed of three male morphotypes: blue clawed males (bulls); orange clawed males; and small males (runts), whose growth is socially suppressed. The effect of the bull's claws on growth suppression of runts was analyzed through a series of manipulations of the bull's second large claws. Runts were raised for 112 days in aquaria paired with (a) an intact bull, (b) a bull with immobilized dactyli and (c) a bull with ablated claws. A group of isolated runts (d) served as a control. Growth of small prawns, their motor and maintenance activities and social interactions with the bull were monitored. The mechanism of growth suppression in runts is based on reduced growth increments per molt, while the rate of molting remained the same as in the fast growing individuals. Claw ablation and dactyli immobilization in bulls resulted in a complete removal of growth suppression in runts which grew similarly to the control. The growth rate of runts raised with bulls seems to be positively related to their social status. © 1992.