Oxygen Consumption During the Metamorphosis of the Parasitic Lamprey, Lampetra Fluviatilis (L.) and Its Non-Parasitic Derivative, Lampetra Planeri (Bloch)

1. Standard oxygen consumption has been measured during the six stages of metamorphosis in both the anadromous parasitic lamprey, Lampetra fluviatilis, and in its non-parasitic derivative, Lampetra planeri. 1. Standard oxygen consumption has been measured during the six stages of metamorphosis in both the anadromous parasitic lamprey, Lampetra fluviatilis, and in its non-parasitic derivative, Lampetra planeri. 2. At 10 °C, the standard rates in larval L. planeri and L. fluviatilis of metamorphosing size were 20.3 and 29.3 μl g−1 h−1 respectively. 3. After a slow rise in oxygen consumption during the initial stages of metamorphosis, the rates reached 50.5 and 60.4 μl g−1 h−1 at stage of 6 of L. planeri and L. fluviatilis respectively. 4. Following the completion of metamorphosis in L. planeri and the development of secondary sexual characters, the mean rate in males rose to 73.3 μl g−1 h−1 compared with a decline in females to 44.1 μl g−1 h−1. 5. Although no circadian rhythm was detectable in the oxygen consumption of larvae, an elevation in the metabolic rate was present during darkness in L. fluviatilis at the end of metamorphosis. 6. Standard oxygen consumption and ventilatory frequency were influenced greatly by temperature, e.g. values for stage 6 of L. fluviatilis rose from 24.3 μl g−1 h−1 and 33.0 beats min−1 at 5 °C to 103.8 μl g−1 h−1 and 98.2 beats min−1 at 15 °C. 7. The results are discussed in the context of the radical changes taking place during metamorphosis and in terms of the differences between larvae and adult and between the life cycles of parasitic and non-parasitic lampreys.