Abstract

Recent studies have shown that juvenile centrarchids undergo significant ontogenetic shifts in habitat use, foraging strategies and perceived predation risk, as well as in the use of conspecific and heterospecific damage-released chemical alarm cues. Microhabitat characteristics, such as habitat complexity and light availability, limit the use of visual cues, which increase perceived risk and can delay the shift to chemical alarm cues. The first experiment explores the behavioural responses of largemouth bass ( Micropterus salmoides ) between 40 and 65 mm SL to heterospecific or conspecific alarm cues in both high and low light conditions, or complex and open habitats. Individuals were exposed to the same chemical cue under both visually limited and unlimited conditions to study the plasticity of behavioural decisions by an individual. The second study was conducted in the field and used three focal size classes of pumpkinseed sunfish ( Lepomis gibbosus ) exposed to conspecific and heterospecific alarm cues in varying levels of habitat complexity. The results demonstrate significantly threat-sensitive behavioural decisions. With low habitat complexity or high light availability perceived risk was low and more significantly individuals demonstrated a foraging response. In high habitat complexity and low light availability perceived risk was high and individuals showed a greater anti-predator response. These results confirm that the shift from anti-predator to foraging responses is a threat-sensitive response and individuals are constantly making behavioural decisions based on the perceived risk and reliability of information available to them.