Respiration and oxygen transport functions of the blood from an intertidal fish, Helcogramma medium (Tripterygiidae)

Abstract

Aquatic and aerial oxygen uptake (O2), ventilation frequency, and oxygen transport properties of the blood were determined for the intertidal fish Helcogramma medium. Ventilation frequency increased in response to decreased environmental PO2 and aquatic O2 was maintained down to a critical PO2 of 30–40 mm Hg. Below PO2 ≃ 30 mm Hg fish intermittently gulped air and finally emerged into air at PO2 ≃18 mm Hg. After 1 h exposure to air O2 decreased to 60% of the aquatic rate and this was accompanied by an increase in blood lactate. Aerobic expansibility was reduced in air (×1.2) compared to water (× 5.5). The Hb concentration was 0.47 ± 0.13 mmol 1−1 and hematocrit 11.55 ± 3.61% indicating a moderate O2-carrying capacity. Oxygen affinity was not especially high (P50 = 19 mm Hg at pH 7.7 and 15°C) and ATP was the predominant acid-soluble phosphate regulating P50. The equilibrium curve was essentially hyperbolic (Hill's n = 1.2) with a marked Bohr effect ϕ = −1.06) and Root effect (saturation depressed by 50% at pH7.1). The pattern of respiration and the respiratory properties of the blood together with observations of the behaviour of the fish during aerial exposure indicated that Helcogramma is adapted to living in a well-aerated environment yet can adequately tolerate short term exposure to low aquatic PO2 or air.