Common Thresher - Biology and Ecology

Biology and Ecology

Common threshers are active, strong swimmers; there are infrequent reports of them leaping completely out of the water. Like the fast-swimming sharks of the family Lamnidae, the common thresher has a strip of aerobic red muscle along its flank that is able to contract powerfully and efficiently for long periods of time. In addition, they have slow-oxidative muscles centrally located within their bodies and a blood vessel countercurrent exchange system called the rete mirabile ("wonderful net"), allowing them to generate and retain body heat. The temperature inside the red muscles of a common thresher averages 2°C (3.6°F) above that of the ambient seawater, though there is significant individual variation. Unlike the pelagic and bigeye threshers, the common thresher lacks an orbital rete mirabile to protect its eyes and brain from temperature changes.

Immature common threshers fall prey to larger sharks. Aside from observations of killer whales feeding on common threshers off New Zealand, adults have no known natural predators. Parasites documented from the common thresher include the protozoan Giardia intestinalis, the trematodes Campula oblonga (not usual host) and Paronatrema vaginicola, the tapeworms Acanthobothrium coronatum, Anthobothrium laciniatum, Crossobothrium angustum, Hepatoxylon trichiuri, Molicola uncinatus, Paraorygmatobothrium exiguum, P. filiforme, and Sphyriocephalus tergetinus, and the copepods Dinemoura discrepans, Echthrogaleus denticulatus, Gangliopus pyriformis, Kroeyerina benzorum, Nemesis aggregatus, N. robusta, N. tiburo, Nesippus orientalis, and Pandarus smithii.