A pufferfish on the defensive will rapidly gulp water into its stomach and inflate to Stay Puft proportions. This stretches their exceptionally elastic skin and causes their small spikes to stand on end. The spiny ball that results can be up to four times its normal size, and the trick is to stay inflated for longer than the would-be predator’s attention span.
However, previous work (as well as Finding Nemo) has suggested that pufferfishes hold their breath while inflated—hindering oxygen uptake and waste excretion through the gills, while limiting the amount of time they can stay puffed up. Well, not so, according to a study published in Biology Letters last week. Pufferfishes are still breathing when they’re inflated.
Georgia McGee of James Cook University and Timothy Clark from the Australian Institute of Marine Science collected black-saddled pufferfish (Canthigaster valentini) by scuba diving in the Lizard Island and Cairns region of the Great Barrier Reef. The fish would swim for 5 to 10 second bursts, and then inflate as they were being captured in hand nets. Back at an aquarium facility, the duo measured pufferfish respiration in clear plastic tanks while they were at rest, during the pre-inflation interval, the inflation period, and the post-deflation recovery. Here’s a (not-so) Puffy McPufferson at rest:
Within a respirometer, each fish was gently squeezed to stimulate inflation. Similar to what happened during their initial capture from the wild, the fish typically inflated after 5 to 10 seconds. Then they stayed inflated between 3.7 and 18 minutes; the average was about 10.1 minutes.
Pufferfishes, they found, have an excellent capacity to breathe while inflated. In fact, oxygen uptake rates increased to five times that of resting levels.
In addition to measuring pufferfish respiration through the gills, the duo also looked at cutaneous respiration through the skin. Other researchers have previously proposed that breathing through the skin might help compensate while the fish is inflated. However, in this species at least, the team found a negligible capacity for cutaneous respiration. Their gills are the primary site of oxygen uptake while they’re inflated.
The team also revealed that the pre-inflation exercise (those 5 to 10 seconds) and the act of gulping water appear to be very metabolically taxing. The pufferfishes took an average of 5.6 hours to recover from these inflation events, which could increase their risk of predation.
Images: Philip Mercurio/www.phil-mercurio.com for G.E. McGee & T.D. Clark, Royal Society 2014