On the diel rhythms in metabolism and activity of post-hatching lesser spotted dogfish, Scyliorhinus canicula

The diel rhythms in metabolic rate ( M_R ) and activity level ( A_L ) were measured for single post-hatching dogfish (weight range, 2.76–10.61 g) at 15° C by the indirect calorimetric method of rate of oxygen consumption ( V O₂) and by video-observation respectively, over a period of 72 b. The mean VO ₂ increased from 62.0 (s.e. 2.9) mg O₂ kg^?1 h^?1 in the daylight hours to 85.5 (s.e. 3.1) mg O₂ kg^?1 h^?1 during the dark (light regíme, 12 h L: 12 h D). The simultaneous measurement of A _L also showed mean night elevation from 0.6 (s.e. 0.2) min h^?1 in the light phase to 14.5 (s.e. 1.6) min h^?1 during the darkness. Bimodal nocturnal activity (BNA) was exhibited by the post-hatching dogfish within the 12 h dark period, with V O₂ increasing from 71.4 (s.e. 2.8) mg O₂ kg^?1 h^?1 before 01.00 hours to 99.5 (s.e. 4.2) mg O₂ kg^?1 h^?1 after 01.00 hours. Similarly, A _L also increased from 8.9 (s.e. I.7)min h^?1 before 01.00 hours to 21.1 (s.e. 2.8) min h^?1 after 01.00 hours. The importance of the results presented to the natural behavioural ecology of the hatching dogfish are discussed.