Oxygen transfer characteristics of the blood of reedfish, Erpetoichthys calabaricus

Abstract

1. 1. Oxygen transport characteristics and phosphate compounds were measured in the blood of reedfish, Erpetoichthys calabaricus, a bimodal breather. Blood from reedfish possessed the following values ( X ̄ ±SD ): hematocrit (21.7 ±0.4%), hemoglobin concentration (7.53± 1.75 g%), red blood cell count (0.45 ± 0.10 × 10 6/mm 3) and oxygen capacity (10.1 ± 2.3 vol%). 2. 2. Although hematocrit, hemoglobin concentration, red blood cell count and oxygen capacity were all highly intercorrelated ( P < 0.01 in all cases), none of these parameters were significantly correlated with sex, weight or length in our sixteen fish sample. 3. 3. Erythrocyte volumes equalled 480 μn 3, showed less variation (CV = 10.4%) and did not correlate with any other measured variable. Blood oxygen dissociation curves were sigmoidal and the P 50's equalled 17.34 ± 3.04 at 1% CO, and 25°C. Mean Bohr shift (Δlog P 50/ΔpH) was −0.274 ± 0.087. Temperature strongly influenced blood oxygen affinity. At 1% CO 2, Δ log P 50/ Δ T equalled 0.026 ± 0.006 ( X ̄ ± SD). These hematological properties indicate that the blood of reedfish is similar to those of other tropical air-breathering species. 4. 4. Concentrations of total phosphate in the erythrocytes and percentage of total phosphate bound as nucleotide triphosphates were high. Surprisingly, 2,3diphosphoglycerate was found which has been reported in the erythrocytes of only two other fish species. 5. 5. Blood characteristics of reedfish exposed to air for 4 hr with one exception (Hill numbers) were not significantly different from water exposed controls. This suggests that the reedfish does not possess blood respiratory mechanisms to facilitate respiration solely by air-breathing.