Siamese fighting fish
Studies have found that Siamese fighting fish often begin with behaviours that require high cost, and gradually decrease their behaviours as the encounter proceeds. This indicates that Siamese fighting fish will first begin an encounter using much metabolic energy, but will gradually decrease, as to not use too much energy, thus making the encounter a waste if the fish is not successful. Similarly, researchers have found that when pairs of male Siamese fighting fish were kept together in the same tank for a three-day period, aggressive behaviour was most prevalent during the mornings of the first two days of their cohabitation. However the researchers observed that the fighting between the two males decreased as the day progressed. The male in the dominant position initially had metabolic advantage; although as the experiment progressed, both fish became equal in regards to metabolic advantages. In regards to oxygen consumption, one study found that when two male bettas fought, the metabolic rates of both fish did not differ before or during the fight. However, the fish who won showed higher oxygen consumption during the evening following the fight. This indicates that aggressive behaviour in the form of fighting has long-lasting effects on metabolism.