Physiological evaluation of seasonal sperm quality in a biannual spawner, Pacific abalone: Effects on in-vitro fertilization and cryotolerance.

Pacific abalone, Haliotis discus hannai, is a highly valuable gastropod mollusk commonly found in Southeast Asia. The present study aims to analyze the seminal plasma quality, sperm quality, and cryotolerance of the Pacific abalone sperm during its reproductive season. The seminal plasma quality was evaluated by analyzing biochemical and metabolite composition, enzymatic activity (superoxide dismutase, catalase, and glutathione), and lipid peroxidation (LPO) activity. The sperm quality was evaluated by analyzing motility, concentration, volume, ATP content, acrosome integrity (AI), plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), DNA integrity, and fertilization potential. The cryotolerance capacity was evaluated by analyzing post-thaw motility, AI, PMI, MMP, and DNA integrity. Seminal plasma osmolarity was significantly higher (1123.3 ± 1.5 mOsmL-1 ) in May compared to other reproductive periods, with Cl- (516.8 ± 0.5 mM) and Na+ (460.2 ± 0.4 mM) as the dominant ions. The seminal plasma pH remained constant at 6.8 throughout the reproductive season. Improved enzymatic activity and lower LPO were detected in May or June. Sperm quality indicators were similar in May and June, except for sperm production. The fertilization potential (May: 93.0 ± 4.4%, June: 86.0 ± 7.2%) and hatching rate (May: 86.6 ± 5.78%, June: 82.3 ± 3.2%) of Pacific abalone were significantly higher in May or June than they were in other reproductive seasons. The motility (May: 50.19 ± 2.35%, June: 49.96 ± 1.60%), AI (May: 44.02 ± 3.46%, June: 42.16 ± 3.61%), PMI (May: 54.12 ± 3.29%, June: 52.82 ± 2.58%), and MMP (May: 44.02 ± 3.46%, June: 42.16 ± 3.61%) of the cryopreserved sperm were similar in May and June compared with those preserved in other reproductive seasons. The DNA integrity of the cryopreserved sperm was similar in May (80.3 ± 6.7%) or June (78.9 ± 7.4%) and had a higher cryotolerance than in other reproductive seasons. Hence, it can be suggested that May and/or June are suitable periods for sperm physiology experiments, artificial reproduction, and sperm cryopreservation of Pacific abalone.