Anesthesia, diagnostic imaging, and surgery of fish have become routine parts of aquatic animal medicine. Anesthesia may be required for simple clinical procedures, diagnostic testing, or more involved surgery. Diagnostic modalities, including radiology, ultrasonography, and endoscopy, can be readily applied to fish and may provide valuable information. Despite some unique challenges, surgery can be performed in fish using basic surgical skills and principles and should be considered as a valid treatment option.