Oxygen consumption of two nearshore marine elasmobranchs, rhinobatos annulatus (Muller & Henle, 1841) and Myliobatus aquila (linnaeus, 1758)

Abstract 1. 1. The oxygen consumption of two nearshore marine elasmobranchs, Rhinobatos annulatus and Myliobatus aguila , was studied under laboratory conditions. 2. 2. Nocturnal peaks in routine oxygen consumption of R. annulatus were observed, while the routine oxygen consumption of M. aquila showed nocturnal and diurnal peaks. 3. 3. The periodogram for R. annulatus suggested a circadian rhythm and for M. aquila a weak tidal rhythm. 4. 4. The specific mass exponents (dimension: μgO 2 /g/hr) are temperature independent and range from −0.15 to −0.33 (common b: R. annulatus −0.18; M. aquila −0.25). 5. 5. Starving the elasmobranchs results in decreases in active, routine and standard oxygen consumption. 6. 6. The maximum rates of oxygen consumption of the two species induced by feeding were 1.42–2.25 and 1.16–4.30 times the routine value for elasmobranchs that have been starved for 40 hr and 162hr, respectively. 7. 7. Apparent SDA for both species showed some variation and ranged from 4.2 to 32.9% (mean: R. annulatus 17.3%; M. aquila 14.0%).