Hybrid catfish, the progeny of channel catfish (Ictalurus punctatus) females by blue catfish (I. furcatus) males, are in high demand by the U.S. aquaculture sector due to their superiority for pond and raceway culture. Typically, older blue catfish (≥5 years of age) are selected for artificial fertilization. Males are sacrificed, their testes are removed, macerated (cut), and sperm is released in an immobilizing media and quantified. It is only once the male has been sacrificed that sperm quantity can be assessed. Observations at our facilities and reports from hatcheries indicate a high degree of variation for testes size, sex hormone profiles, and sperm traits. It is essential to establish links between paternal age and reproductive success, as it is apparent that advanced paternal age causes changes to sperm that can have consequences for offspring health and performance through molecular changes and DNA mutations. Thus, a better understanding of interlinked physiological and molecular processes associated with paternal ageing will advance our male diagnostic toolbox.
This study investigated reproduction of blue catfish males aged 2 to 10 years, focusing on key reproductive parameters. A total of 103 males were sampled, representing 9 age classes. Fish morphometric data were collected, and blood was drawn to quantify testosterone (T), 11-Ketotestosterone (11-KT), osmolality, and ions. Histological images of testes assessed stages of spermatogenesis. Sperm were activated and kinematics analyzed. Testes transcriptome was also profiled across immature and mature individuals. Preliminary results showed that sperm were detected in 13%, 64%, and 100% of males at 2, 3, and 4+ years of age, respectively. Sperm kinematic traits increased at 4 years of age with a high degree of variation among males (Fig. 1AB). To identify differentially expressed genes (DEGs), pairwise differential gene expression analysis was performed between 2 vs. 4-year-old males (Fig. 1C). The numbers of upregulated DEGs and downregulated DEGs were 2,088 and 981, respectively. A similar comparison was conducted between 4 vs. 7-year-old fish, showing 18 downregulated DEGs and 19 upregulated DEGs (Fig. 1D). These data are paramount for designing studies to manipulate and control testes development to enhance production efficiency.