Age-related reproductive performance and transcriptome profiling of testis in male blue catfish, Ictalurus furcatus

Catfish farming is the largest aquaculture industry in the U.S., where hybrid catfish produced by channel catfish, Ictalurus punctatus ♀ × blue catfish, I. furcatus ♂, represent > 50% of the harvest. Previous studies indicated a high degree of variation in reproductive performance among individuals. Therefore, it is crucial to establish a connection between paternal age and reproductive success. This study investigated the reproduction of 103 blue catfish males aged 2 to 10 years. Morphometric data were collected, and blood was drawn to quantify testosterone (T), 11-ketotestosterone (11-KT), osmolality, and ions. Histological images of the testis assessed stages of spermatogenesis, and sperm were activated for kinematic analysis. The testis transcriptome was profiled across distinct ages, 2, 4, 7, and 9. For fish aged 2 to 10 years, those over 7 years had the largest size, with a rapid increase until age 7 and a slight increase afterwards. Absolute sperm production was affected by age, with the highest levels observed at age 6, followed by a decreasing trend. T and 11-KT did not increase after age 6, while sperm kinematics were not impacted by age. Transcriptomics identified 5220 differentially expressed genes (DEGs) in all comparisons. The most DEGs were identified at age 7 with 2261 down-regulated and 1824 up-regulated genes. Functional enrichment revealed significant changes in axoneme, motile cilium, and sperm flagellum at age 7. In contrast, immune processes were increased in the testis at age 9 with viral and bacterial defense responses. Results suggest that farmers should maintain consistent supplies of age 6 and 7 males to increase hatchery efficiency.