Catfish is the most important species in US aquaculture, accounting for 70% of freshwater production. The production of hybrids of female channel catfish (Ictalurus punctatus) and male blue catfish (I. furcatus) constitutes over 50% of the total harvest due to their superior production traits and enhanced disease resistance. However, hybrids cannot be produced naturally, and male must be euthanized for sperm collection. An appropriate storage condition is essential to preserve the sperm’s ability to fertilize eggs during the female spawning season. Cryopreservation is a widely used method for sperm storage. However, it has been shown to affect sperm gene expression in many vertebrate species. A high degree of individual variability among cryopreserved sperm was reported, resulting in huge variations in hatch rate. Since high-quality gametes are the prerequisites for hybrid catfish reproduction, understanding the molecular mechanisms associated with sperm quality is critical for the accurate prediction of hatching rate and offspring performance in hatchery environments.
In this study, sperm collected from 28 adult male blue catfish has been experienced a cryopreserved process. After cryopreservation, the sperm was thawed and fertilized with eggs from 3 female channel catfish to test the embryo hatching rate. The average embryo hatching rates ranged from 14% to 63%. RNA-seq and DNA methylome sequencing experiments were performed to investigate the gene expression and epigenetic profiles of each sample. After sequencing adapter and low-quality reads removal, the RNA-seq reads from 28 samples were aligned to the blue catfish genome, achieving an average mapping rate of 81.98% (from 70.7% to 91.7%). A total of 33,043 expressed genes remained after filtering out those with low expression level (RPKM < 1) in more than 6 samples. Differential expressed gene analyses showed that 1,400 genes were up-regulated and 4,611 genes were down-regulated in sperm with high embryo hatching rates. Compared to the sperm with low hatching rates, genes involved in cytokine-cytokine receptor interaction, regulation of actin cytoskeleton and calcium signaling pathway were significantly up-regulated in high hatching rate sperms, suggesting that the sperm with stronger immune responses and enhanced cell movement are more likely to result in hatching success. In contrast, up-regulated genes in sperm with low hatching rates were enriched in RNA degradation, mitophagy and autophagy pathway, suggesting that those may experience decreased motility due to the reduced energy and protein production. Our findings provide valuable insights into the molecular mechanisms behind male reproduction success. By identifying these key genes, we will be able develop biomarkers to predict hatching success and potentially improve breeding strategies in catfish aquaculture. Our research contributes to a deeper understanding of reproductive performance on the male side and paves the way for efficient hybrid catfish production.