Resting metabolic rate and social status in juvenile giant freshwater prawns, Macrobrachium rosenbergii

Forty post-larval giant freshwater prawns (Macrobrachium rosenbergii) were weighed, measured, marked and placed in groups of 4. Social interactions were screened daily, moults were recorded and the nature and stability of dominance interactions characterised. Half of the prawns were screened for resting oxygen consumption before group formation. In most groups, one or two individuals ('dominants') consistently won the majority of interactions in which they were involved, while others ('subordinates') consistently lost; the remainder were classified as of intermediate social status. Prawns lost more fights on the day before a moult, but despite this. rank was retained after moults. Neither initial size nor growth rates varied with status, but prawns that became dominant had significantly higher resting metabolic rates before group formation than those that became subordinate. Thus in M. rosenbergii the outcome of aggressive interactions can be predicted from the metabolic physiology of the animals although whether the relationship is causal remains to be determined.