Dissolved oxygen tolerance of <em>Hippocampus abdominalis</em> across varying temperature regimes

Abstract

To understand the dissolved oxygen tolerance of Hippocampus abdominalis during transportation or cultivation at different water temperatures, this study investigated the patterns of oxygen consumption and activity changes in H. abdominalis (with body lengths of 11.55-12.05 cm and weights of 4.60-6.19 g) as the dissolved oxygen (DO) levels in the water decreased. The experiment utilized the static water respiration chamber method, using a water bath to control the temperature with a variation not exceeding 1℃. Three experimental temperature gradients were designed: 14℃, 19℃, and 24℃, with three repetitions for each group and a blank control group set for comparison. Results showed‌: suffocation point (±SD) were (0.18±0.03) mg/L at 14°C, (0.20±0.05) mg/L at 19°C, and (0.21±0.02) mg/L at 24°C. Elevated temperatures reduced DO saturation levels and increased the suffocation point. During the asphyxiation phase (Phase I: onset to first death), oxygen consumption rates (OCR) were 0.29 mg/(g·h), 0.46 mg/(g·h), and 0.51 mg/(g·h), respectively at three temperatures. During the mortality phase (Phase II: first death to 100% mortality), OCR were 0.02 mg/(g·h), 0.01 mg/(g·h), and 0.01 mg/(g·h). Under salinity 28.25 and pH 8.54, both DO parameters and suffocation point exhibited temperature dependency. Phase I OCR increased with temperature, with 14°C group significantly lower than 19°C/24°C groups. Phase II OCR at 14°C was slightly higher than in other groups. All groups showed a significant OCR decline with DO reduction. H. abdominalis employed a ‌conformist respiratory strategy, modulating oxygen consumption to adapt to hypoxia. Metabolic rates rapidly escalated during asphyxiation but minimized under critical hypoxia with narrow DO variation margins. The study demonstrates‌an immediate high-oxygen-consumption response under DO stress. Poor hypoxia tolerance with stringent DO requirements. Dissolved oxygen is closely related to fish metabolism and energy consumption. The large-scale breeding of juvenile seahorses requires stringent conditions, where high-quality germplasm supply is a prerequisite for successful breeding, and the survival rate during transportation ensures the stable supply of germplasm. Real-time monitoring of DO levels, combined with behavioral observations, is essential for standardizing protocols in aquaculture and transport operations. This study provides theoretical support for oxygen management during transportation by quantitatively analyzing the oxygen consumption rate.