The anabantoids are a group of c. 137 species of air-breathing freshwater fishes found in Africa and southern Asia. All anabantoids have a pair of suprabranchial chambers that each house an air-breathing organ known as the labyrinth apparatus: a complex bony structure lined with thin, highly vascularised respiratory epithelium. The labyrinth apparatus allows anabantoids to extract oxygen from air and is a morpho-physiological innovation that has had a dramatic influence on the behaviour of these fishes. Air-breathing influences a wide range of anabantoid behaviours, including territorial displays, courtship and breeding and parental care and also equips these fishes to persist in hypoxic and polluted water. These traits also make anabantoids successful invaders of novel habitats, a global problem compounded by their popularity in the aquarium trade. By reviewing the functionality and evolution of air breathing in anabantoids, this review aims to examine the role of the labyrinth apparatus in modulating behaviour within this group. The anabantoids are a fascinating group and have often been cited as a model organism due to the stereotypical and easily identifiable behaviours that they adopt during social interactions. They also provide a unique opportunity to further our understanding about how fishes adapt their behaviour in response to an extreme environment, whilst limited by their own physiological constraints.

1Siamese fighting fish, Betta splendens, have been extensively studied due to their aggression 2 and stereotypical displays. Many studies have focused on their characteristic opercular 3 flaring, while the less aggressive and less energetically costly lateral display have been 4 comparatively understudied. Many factors have been shown to influence aggression in 5Bettas, notably body length and the personality trait of boldness, however, the role that colour 6 plays in determining an individual's aggressiveness is much less clear. The role of colour has 7 only been briefly studied, and based on human interpretations of colour, i.e. limited to what 8 the receivers' eyes and sensory systems actually can process and discriminate, with results 9 suggesting blue males are more aggressive than red males. Using male-male interactions, 10 measuring opercular flaring and lateral display we found that colour and personality do play a 11 role in determining the degree of aggressiveness in Betta splendens. Blue-finned males were 12 more aggressive, performing longer lateral displays more frequently. Blue fins are a 13 phenotype observed in wild type males and is likely selected for to allow visual cues to travel 14 through the murky water they inhabit. Body mass was positively correlated with lateral 15 display frequency, and opercular flare frequency and duration. Finally, neophobic individuals 16 -individuals that were less willing to approach a novel object -were more aggressive, 17 performing significantly more lateral displays. This indicates that personality may impact 18 fighting strategy, with males either choosing to end conflicts quickly with more aggressive 19 displays or to outlast their opponent with less energetically costly displays. 20 21