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On the roofs of subtidal crevices, the giant cuttlefish (Sepia apama) of southern Australia lays clutches of lemon-shaped eggs which hatch after 3 to 5 mo. Diffusion of oxygen through the capsule and chorion membrane to the perivitelline fluid and embryo was modelled using the equation [[V.sub.o].sub.2] = [[G.sub.o].sub.2] ([[P.sub.o].sub.2out] - [[P.sub.o].sub.2in]), where [[V.sub.o].sub.2] = rate of oxygen consumption, [[G.sub.o].sub.2] = oxygen conductance of the capsule, and [[P.sub.o].sub.2] values = oxygen partial pressures across the capsule. During development, [[V.sub.o].sub.2] rose exponentially as the embryo grew, reaching 5.5 [micro] 1 [h.sup.-1] at hatching. Throughout development, the capsule dimensions enlarged by absorption of water into the perivitelline space, increasing [[G.sup.o].sub.2] by a combination of increasing surface area, and decreasing thickness of the capsule. These processes maintained [[P.sub.o].sub.2] high enough to allow unrestricted [[V.sub.o].sub.2] until shortly before hatching. Diffusion limitation of respiration in hatching-stage embryos was demonstrated by (1) increased embryonic [[V.sub.o].sub.2] when [[P.sub.o].sub.2out] was experimentally raised, (2) greater [[V.sub.o].sub 2] of resting individuals immediately after hatching, and (3) reduced [[V.sub.o].sub.2] of hatchlings at experimental [[P.sub.o].sub.2] levels higher than [[P.sub.o].sub.2in] before hatching. Thus, low [[P.sub.o].sub.2in] may be the stimulus to hatch. Potential problems of diffusive gas-exchange are mitigated by the relatively low incubation temperature (12 [degrees] C), which may be a factor limiting the distribution of the species to cool, southern waters.

Tarpon have high resting or routine hematocrits (Hct) (37.6±3.4%) and hemoglobin concentrations (120.6±7.3 g l−1) that increased significantly following bouts of angling-induced exercise (51.9±3.7% and 142.8±13.5 g l−1, respectively). Strenuous exercise was accompanied by an approximately tenfold increase in blood lactate and a muscle metabolite profile indicative of a high energy demand teleost. Routine blood values were quickly restored only when this facultative air-breathing fish was given access to atmospheric air. In vitro studies of oxygen transport capacity, a function of carrying capacity and viscosity, revealed that the optimal Hct range corresponded to that observed in fish under routine behaviour. During strenuous exercise however, further increase in viscosity was largely offset by a pronounced reduction in the shear-dependence of blood which conformed closely to an ideal Newtonian fluid. The mechanism for this behaviour of the erythrocytes appears to involve the activation of surface adrenergic receptors because pre-treatment with propranolol abolished the response. High levels of activity in tarpon living in hypoxic habitats are therefore supported by an elevated Hct with adrenergically mediated viscosity reduction, and air-breathing behaviour that enables rapid metabolic recovery. [Copyright &y& Elsevier]