Metabolic rate of embryonic little skate,Raja erinacea (Chondrichthyes: Batoidea): The cost of active pumping

Abstract

Near-hatching embryonic little skates, Raja erinacea, are highly active within their egg capsules, displaying a characteristic tail beating, which pumps water through the capsule. We measured the metabolic rate of late-stage embryos to determine whether oxygen sufficient for the embryo's needs will diffuse through the egg capsule, and to assess the energetic cost of tail beating. Metabolic rate was inferred from oxygen consumption rates while embryos were in the capsules, unencapsulated, and anesthetized and unencapsulated. Anesthesia inhibited voluntary movements, including tail wagging, allowing an estimate of the standard metabolic rate (SMR). Averaged over five embryos, the SMR was 0.032 ± 0.004 ml O 2 g -1 hr -1 . There was no significant difference in metabolic rate between encapsulated (0.058 ± 0.009 ml O 2 g -1 hr -1 ) and unencapsulated (0.049 ± 0.009 ml O 2 g -1 hr -1 ) skates. Tail beating was found to be energetically expensive, requiring a 53%-81% increase over the SMR. From literature values for the oxygen permeability of the egg capsule we conclude that tail beating is required to supply sufficient oxygen to the embryonic skate. This observation is consistent with the proposal that actively pumping water through the capsule, by tail beating, has played an evolutionary role in the shape of the capsule.

Identification of skate nursery habitat in the eastern Bering Sea

“…EBS skates may not require attachment structure as the EBS slope currents are slower than those of rocky reef nursery sites in Aleutian Island passes (Reed & Stabeno 1999). Moderate currents such as those along the upper slope of the EBS may create sufficient water flow across the egg surface to sustain metabolic processes (Hoff 2007, 2008, Leonard et al 1999) and ensure eggs are not covered with sediments, yet moderate enough not to scatter eggs up onto the shelf or into deeper waters to suboptimal habitat.…”

Influence of body mass, food concentration, temperature and filtering activity on the oxygen uptake of the appendicularian Oikopleura dioica

“…Commonly used in fisheries as an anaesthetic, MS-222 is known to suppress motor activity. Only the respiration derived from muscular movement is affected among fishes (Leonard et al 1999), whereas MS-222 does not affect cutaneous respiration. For appendicularians, MS-222 does not affect the vital activities: spiracles and heart continue to function normally (authors' pers.…”

Dogmas and controversies in the handling of nitrogenous wastes:Osmoregulation during early embryonic development in the marine little skate Raja erinacea; response to changes in external salinity

“…There were no differences between these embryos and those in the present study (N=4-6); for example, urea in the embryonic tissue (382±26.2·mmol·kg -1 ·tissue·water) and yolk (448±45.2·mmol·kg -1 ·tissue·water) of the intact embryos was not significantly different from the values in decapsulated 4-month embryos presented in this study. Furthermore, Leonard et al (1999) compared metabolic rate (i.e. oxygen consumption) in late term intact versus decapsulated embryos and found no significant differences.…”