The world's fastest swimming fishes - in relation to their size - are coral reef fish larvae on their way to settle on reefs, and new evidence has shown that they also use more oxygen than any known ectothermic vertebrate.
According to new research published in the Proceedings of the Biological Society which looked at two damselfishes - Chromis atripectoralis and Pomacentrus amboinensis - the rapid swimming speeds of pre-settlement larvae go hand in hand with the highest rate of oxygen uptake ever seen in ectothermic vertebrate animals.
"As expected, these high rates of oxygen uptake occur at the cost of poor hypoxia tolerance. However, hypoxia tolerance is needed when coral reef fishes seek nocturnal shelter from predators within coral colonies, which can become severely hypoxic microhabitats at night," wrote the authors.
The research found that a striking transformation took place at night in which the capacity for rapid oxygen uptake fell while the ability for high-affinity oxygen uptake at low oxygen levels increased - allowing the fish to withstand hypoxic conditions.
"This transition to hypoxia tolerance is needed when they settle on the reef; this was strengthened by our finding that small resident larvae of Acanthochromis polyacanthus, a damselfish lacking a planktonic larval stage, do not display such a transition, being well adapted to hypoxia and showing relatively low maximum rates of oxygen uptake that change little with age."
For more information see the paper: Nilsson GE, Ostlund-Nilsson S, Penfold R, Grutter AS (2006) - From record performance to hypoxia tolerance: respiratory transition in damselfish larvae settling on a coral reef. Proc Biol Sci. 2006 Sep 26.