Fish handling and ultrasound procedures for viewing the ovary of submersed, nonanesthetized, unrestrained channel catfish

This study addressed the development of rapid, straightforward, and minimally stressful procedures for the ultrasound imaging of ovaries of channel catfish Ictalurus punctatus in a commercial hatchery setting. The objectives were to (1) describe the ultrasound imaging equipment and settings used, (2) describe the fish handling procedures during imaging, and (3) illustrate image orientation with respect to the physical positioning of the probe and the catfish. Ultrasound images of the ovaries of channel catfish were recorded as digital video recordings (audio video interleave format) and as still images (ultrasound image format files). This study integrated the use of nonanesthetized, submersed fish within a recirculating tank system or portable container and a submersed waterproof probe, which enabled us to use water as a transmission medium for ultrasound. This allowed us to image the fish in ventral recumbency (upright swimming position) without using a physical restraint in the tank system, or by positioning the fish in the portable container by adjusting the position of its caudal peduncle with one hand and that of the probe with the other hand. The ease of using this technique allows it to be employed as a systematic method for fish handling under laboratory and hatchery conditions. The detailed ultrasound imaging procedures and instrument control settings reported can be used in future testing, improvement, and standardization of procedures for viewing ovaries in channel catfish and potentially other species