The Agonistic Behaviour of the Three Male Morphotypes of the Freshwater Prawn Macrobrachium Rosenbergii (Crustacea, Palaemonidae)

The agonistic behaviour of the freshwater prawn, Macrobrachium rosenbergii, was studied in the laboratory. One hour long contests were conducted between prawns matched to size in each of the three sexually mature male morphotypes of this species; Small Males, Orange Clawed males and Blue Clawed males. An agonistic ethogram was established, consisting of 18 different acts. These acts were classified into indicators of dominance or subordinante following the application of cluster analysis. Prawns contests consisted usually of 3 phases: pre-escalated fighting phase, escalated fighting phase and post- escalated fighting phase. Contest phases differed both in the frequency of several acts and in the distribution of acts between the eventual winner and loser. In addition, the relative orientation and elevation of the opponents changed across phases. The inter and intra- individual sequences of acts of the winner and loser during the escalated fight were studied. Despite the similarity found in the behaviour of the two opponents during the escalated fighting, the eventual winner could be predicted by the relative number and duration of nips or by the relative number of times in which Complete and Incomplete- Lifting (two major displays of fight) were performed simultaneously with the snapping of the claws. Differences found among morphotypes pointed out a tendency of shifting from interactions with physical contact towards ritualized interactions without physical contact. This was correlated with the morphotypic developmental pathway and the concomitant increase of claw size.