Hypoxia tolerance in a selectively bred F4 population of blunt snout bream (Megalobrama amblycephala) under hypoxic stress

Abstract

Blunt snout bream (Megalobrama amblycephala) is a hypoxia-sensitive fish species. A sudden decrease in the dissolved oxygen (DO) content in the pond will cause massive death. Therefore, breeding of new hypoxia-tolerant strains is important for blunt snout bream aquaculture. From 2007, selective breeding under hypoxic stress was performed on the wild M. amblycephala (F0) population from Poyang Lake, China. In 2015, the selectively bred hypoxia-tolerant F4 population was obtained, which the LOEcrit (loss of equilibrium) was 0.54 mg·L−1, 0.89 mg·L−1 and 1.28 mg·L−1 at 10 °C, 25 °C and 30 °C, respectively. And the LOEcrit in the ‘Pujiang No.1’ breed (control group) was 0.72 mg·L−1, 1.03 mg·L−1 and 1.41 mg·L−1 at 10 °C, 25 °C and 30 °C, respectively. Compared with the control group, the hypoxia-tolerant population had a significantly (P < 0.01) lower critical oxygen tension value at which they lost equilibrium (LOEcrit) at the same temperatures. Furthermore, when hypoxia-tolerant population was exposed to 4 or 7 days of hypoxia (DO = 2.0 mg·L−1) at 10 °C, the average protruding gill lamellar height and mean gill lamellar area were significantly (P < 0.01) smaller than those of the control group. Simultaneously, in order to enhance their blood oxygen-carrying capacity to adapt to the hypoxic environment, the erythrocyte count and hemoglobin concentration of the hypoxia-tolerant population were significantly increased, and were much higher (P < 0.01) than those of the control group under hypoxia treatment (DO = 2.0 mg·L−1). These data showed that the hypoxia-tolerant F4 population had high potential for coping with hypoxic stress, and we can get a hypoxia-tolerant strain of blunt snout bream by continuous hypoxia breeding in aquaculture.