Authors:

Kaylan Martin

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About Paper:

Male blue catfish (Ictalurus furcatus) are a commercially important species that when crossed with female channel catfish (I. punctatus) produce a hybrid that accounts for >50% of U.S. catfish production. Sperm collection from male blue catfish is a lethal procedure, so it is crucial to understand how age and seasonality impact sexual maturity for selection. The objectives of this study were to follow male blue catfish for 34 months to quantify changes in body morphometrics, sex steroid hormones, and testicular development and gene expression as fish age and mature. Male blue catfish (n=5) were sampled every other month from August 2021 to February 2024. Weight, length, and blood samples for hormone analysis were taken before lethal dissection of testes. Testes were weighed and a piece (~1 g) of testis was kept in neutral-buffered formalin for histological analysis. Additional testis samples (~1 g) were snap frozen in liquid nitrogen for RNA extraction. RNA was extracted and sent for sequencing. Bioinformatic analysis was ran to determine differential genes between ages and seasons. Gonadal Somatic Index (GSI) and the Spermatogenic Maturity Index (SMI) were calculated based on cell types found in histological samples at different developmental stages. We observed significant differences (p ≤ 0.05) in body length, weight, and testes weight as fish aged. GSI and sex steroid hormone levels were the highest at Age 4 during the spawning season, indicating maturation and spawning readiness. SMI values indicated that as fish aged, sperm cells developed, and fish were sexually mature at Age 4. Differential genes (DEGs), implying maturity and gonadal development, were also expressed between ages 2, 3, and 4 when sampled during and out of spawning season, with the highest amount of DEGs expressed between Age 2 sampled in winter and Age 4 sampled in summer. These findings improve our understanding of maturation and development in male blue catfish throughout early ontogeny.

Source:

Auburn University / College of Agriculture / 2025

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Co-authors:

Kaylan Martin