The United States catfish industry appears sustainable after the adoption of superior channel catfish, Ictalurus punctatus female × blue catfish, I. furcatus male hybrids. However, there are still challenges in reproductive management due to the nature of the breeding process. For instance, blue catfish males reach maturity after 4-7 years. Unlike other fish in which sperm can be extracted by stripping, sperm collection from blue catfish is accomplished by removal and maceration of testes. As the males must be sacrificed to obtain sperm, a substantial investment in sperm production is required. Typically, a mechanistic relationship exists between sperm form and function, where it is predicted that longer sperm have enhanced swimming and higher fertility. As such, a complete assessment of sperm morphology will provide important information to support captive breeding and broodstock management for hybrid catfish production. The aim of this study was to link sperm ultrastructure and morphometrics to sperm swimming kinematics of blue catfish.
Blue catfish males (n = 43) were seined from aquaculture ponds. Males were euthanized and testes dissected, washed with Hank’s balanced salt solution, and sperm cells extracted for assessment of form and function. Computer Assisted Sperm Analysis (CASA) software was used to quantify sperm velocity, which is the primary determinant of fertilization success. Males were ranked based on mean velocity and separated into two groups: high (n = 8; 200.5 ± 8.9 µm/s) and low velocity (n = 8; 158.0 ± 5.4 µm/s) groups. Sperm from these high- and low-quality males were then fixed in glutaraldehyde and imaged with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for morphometric and ultrastructure analyses.
Preliminary results show that blue catfish sperm are biflagellar (Fig 1a), lack an acrosome (Fig 1bc), and are differentiated into a head, midpiece, and flagellum (Fig 1bc). Mean (± SD) head length was 1.74 ± 0.32 µm and width was 2.21 ± 0.25 µm. The midpiece was 1.42 ± 0.30 µm in length and 2.75 ± 0.30 µm in width, while the length of flagella was 81.53 ± 6.87 µm. SEM shows several sperm with unidentified projections on the tip of their heads. F
b
We are currently examining the linkage between sperm morphology and swimming kinematics to assist with stock selection