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The large size variation of Macrobrachium amazonicum reflects a complex population structure that consists of four morphotypes, called TC (Translucent Claw), CC (Cinnamon Claw), GC1 (Green Claw 1), and GC2 (Green Claw 2). The effect of the largest morphotype (GC2) claws on development and behaviour of the smallest male morphotype (TC) was analysed through manipulations of the large prawn’s second pair of claws. TC males were paired for 75 days in aquaria with (a) an intact GC2, (b) a GC2 with immobilized dactyls, and (c) a GC2 without chelipeds. Isolated TC males served as a control. The maintenance activities of TC males and social interactions with the GC2 morphotype were monitored. Survival and growth of TC males was lower in relation to the control when they were paired with intact GC2 males. Aggressive interactions were carried out almost exclusively by GC2 and strongly affected the behaviour of the small prawns. The absence of chelipeds and immobilization of dactyls in GC2 prawns reduced the negative effect on the development of TC males and agonistic behaviour. The social interactions between GC2 and TC prawns reflect a stable dominance hierarchy. The large claw of the GC2 morphotype plays a major role in the social interaction.

Integrated multitrophic aquaculture (IMTA) is an alternative means to optimize feed usage in aquaculture which combines species of different trophic levels. The addition of substrate to IMTA has also been used to promote a lower release of phosphorus, thus minimizing eutrophication and impacts of effluents. In these aquaculture systems, the zooplankton community is important because it acts as a link in trophic chains. This study aimed to verify the dynamics and the structure of the zooplankton community in IMTA (tilapia-prawn), in response to trophic conditions in earthen ponds with different substrates. The object of the study was 12 earthen ponds organized in three treatments: no substrate (control), geotextile substrate, and bamboo substrate. Zooplankton samples were taken biweekly through a water bilge pump. Rotifers and microcrustaceans were identified and counted to determine changes in community diversity during the experiment. Eutrophication was determined throughphosphorus and chlorophyll water concentrations. There were no differences in zooplankton communities among treatments, even though increases in levels of eutrophication of the system heavily influenced this community, by altering its diversity and abundance. Small organisms were the most representative ones under polyculture eutrophic conditions.