Development of air breathing in the bristlenose pleco (<i>Ancistrus cirrhosis</i>)

The bristlenose pleco ( Ancistrus cirrhosus) is a species of Loricariidae armored catfish that is thought to facultatively breathe air using its highly vascularized stomach when faced with hypoxic aquatic environments. The main goals of this study were to determine the timing of developmental onset of air breathing and examine the influence of temperature and aquatic oxygen availability on air breathing behavior in A. cirrhosus from juveniles to adults. To examine the timing of developmental onset of air breathing, we tested for air breathing behavior in juveniles beginning at 1 cm in length through adults at 8 cm in length by exposing each fish to an acute gradual decrease in aquatic oxygen content from 100% air saturation down to 8% air saturation over a 50 min period. Juvenile fish first began to breathe air at body lengths between 2 and 3 cm. Fish with body lengths above 3 cm all breathed air when hypoxia challenged. To determine how fish respond to temperature and oxygen availability we subjected fish ranging in length from 2 to 14 cm to three acute temperatures (20°C, 25°C, and 30°C) and progressive hypoxia (100%, 30%, and 15% air saturation). Gill ventilation frequency (F g ) and air-breathing frequency (F abo ) were monitored hourly at each temperature-oxygen combination. In 100% air saturation as temperatures increased from 20°C to 30°C, fish F abo increased from almost no air breathing at 0.6 breaths hr -1 to frequent 8.5 breaths hr -1 . At all temperatures, increasing hypoxia led to significantly greater F abo . At 15% air saturation, fish at 20°C increased their F abo to 6.9 breaths hr -1 when compared at 100% air saturation, while those at 30°C increased to 22.5 breaths hr -1 . The Q 10 for F abo at 30 and 15% air saturation were 4 and 6, respectively. With increasing temperature F g increased to a lesser extent than F abo at all levels of oxygen air saturation with Q 10 being close to 2. The developing A. cirrhosus can take advantage of the aerial environment once they reach 2 cm in length when exposed to aquatic hypoxia. Oxygen needs in response to increases in temperature are met by greater increases in F abo than F g and individuals appear to become obligate air breathers at higher temperatures. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.