A new indicator of hypoxia tolerance in abalone, developed based on heart rate fluctuations

Abstract

China is the largest producer and consumer of abalone worldwide, harvesting nearly 140,000 tons in 2016. Due to rising temperatures, intensive culture patterns, and other factors, hypoxia has become a serious problem for Chinese abalone aquaculture, especially in Fujian Province. A hypoxia-tolerant strain is needed for the sustainable development of abalone farming. However, it is problematic to evaluate hypoxia tolerance in abalone. Usually, the traditional analyses cause severe damages to the sampled individuals, possibly including disorders in gonad development or death and these samples could hardly be used for breeding. Here, it was found that abalone heart rates characteristically exhibited a sharp decline below a certain DO threshold, which can be referred to as the breakpoint of dissolved oxygen (BPDO). The BPDOs were sensitive to temperature – the higher acclimation temperature or experimental temperature would increase BPDO. To verify the utility of BPDO as an indicator of hypoxia tolerance in abalone, an acute stress test was conducted with 32 abalone individuals under severe hypoxia (~0.5 mg/L) and significant negative correlations between BPDO and attachment duration, and between BPDO and survival time were found. The BPDO method was advantageous, as it supported individual detection and survival, which allows the selection and retention of hypoxic-tolerant individuals for further genetic breeding. BPDOs at different temperatures also provide important references for abalone aquaculture.