Assessment of Swimming Performance, Body Size and Aggression in a Dwarf Cichlid, Nannacara anomala

Daigle, William R

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Assessment of Swimming Performance, Body Size and Aggression in a Dwarf Cichlid, Nannacara anomala

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In this study, I investigated the ritualized fights of male Nannacara anomala to show that each distinct phase (lateral display, tail beating, and mouth wrestling) of the fight is used to assess a different aspect of resource holding potential (aggressiveness, body size and swimming performance). When animals go into an agonistic encounter, they often have little or no previous knowledge of their opponent's fighting ability (or resource holding potential). Assessment is the process by which strangers gain information about each other through repetition of informative behaviors. Generally fights are ritualized so that specific behaviors are associated with distinct phases within the fight. Aggressiveness of fish was established by measuring response time to an aggressive conspecific. Weight was used as a measure of body size. Swimming performance (stamina and maximum swimming speed) was determined by swimming each fish in a variable speed flow tank. If all fights are taken into consideration, weight is the only factor for which winners were significantly different from losers (p = 0.009). However, if the fights are classified by the phase in which they ended, fights ending in tail beating have larger winners (p = 0.003) and fights ending in mouth wrestling have faster winners (p = 0.008). Opponents are using early stages of fights to assess body size and escalated stages to assess performance characteristics.

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