Abstract
Koi carp (Cyprinus carpio) are one of the most popular ornamental fish in the United States and throughout the world, and represent one of the most common fish species presented to clinicians by owners seeking medical care for their fish pets. Koi mature at 2–3 years, are not sexually dimorphic, and juveniles are impossible to sex without the use of advanced imaging or biopsy. The use of ultrasonography to investigate for disease in koi patients is recommended1,2 and there are several reports where ultrasonography was able to aid in the diagnosis of pathology in koi3-6. Furthermore, ultrasonography has been used extensively in aquaculture to determine sex or sexual maturity of individuals for over 30 years in 21 different species.7 To date no published study has evaluated normal ultrasonographic anatomy of koi or has investigated the feasibility of determining gender of juvenile koi fish by ultrasonographic examination. The goals of this study were to 1) develop a comprehensive reference of normal koi ultrasonographic anatomy and 2) to develop a non-invasive diagnostic method for juvenile koi fish sex determination.
Coelomic ultrasound was performed on 45 clinically healthy juvenile koi. Fifteen fish were examined at three different time points; roughly 6 months, 12 months, and 18 months of age. Ultrasonographic examination was performed with fish under general anesthesia (100 mg/L of buffered tricaine methanesulfonate). The highest possible frequency transducers were used to examine the fish (6–18 MHz) and were chosen to optimize imaging according to fish size. Longitudinal and transverse images and cine loops were acquired and stored for each patient. Identification of organs, location, relative echogenicity and echotexture were evaluated for major organs including the liver, gall bladder, gastrointestinal tract, cranial and caudal kidney, reproductive tract, heart, and swim bladder. At the completion of the ultrasonographic examination, fish were euthanized and a complete necropsy was performed with gender verification determined by gross inspection of the gonad tissues.
Preliminary results show that liver, gall bladder, gastrointestinal tract, caudal kidney, reproductive tract, heart and swim bladder were readily visible in all fish and at all time points. For all fish and time points, it was impossible to confidently distinguish the spleen from the surrounding coelomic viscera. The cranial kidney was progressively easier to identify as fish grew larger and matured. Fish sex was correctly determined in 80% at 6 months of age, 93% in 12 month old fish, and 100% at 18 months. These results demonstrate that ultrasonographic evaluation of koi, even when immature, can provide a wealth of data for the veterinary practitioner. The ultrasound data reported in this study may serve as a baseline reference which may help clinicians in the diagnosis of fish disease. Furthermore, this study has demonstrated that the use of ultrasonography for gender determination can be performed as an accurate and non-invasive way to sex juvenile koi fish.
Acknowledgements
The authors would like to acknowledge the financial support of the UC Davis Center for Companion Animal Health and to thank the doctors, technical staff and veterinary students of the UC Davis Aquatic Animal Health Service and the Companion Exotic Animal Medicine and Surgery Service for their collaboration and help with this project.
* Presenting author
+ Student presenter
Literature Cited
1. Roberts HE, Weber SE, Smith SA. 2010. Nonlethal diagnostic techniques. In: Fundamentals of Ornamental Fish Health. Ames (IA): Wiley-Blackwell; p 172–184.
2. Saint-Erne N. 2010. Diagnostic techniques and treatments for internal disorders of koi (Cyprinus carpio). Vet Clin North Am Exot Anim Pract. 13:333–347.
3. Lewbart GA, Spodnick G, Barlow N, Love NE, Geoly F, Bakal RS. 1998. Surgical removal of an undifferentiated abdominal sarcoma from a koi carp (Cyprinus carpio). Vet Rec-English Ed. 143(20):556–557.
4. Raidal SR, Shearer PL, Stephens F, Richardson J. 2006. Surgical removal of an ovarian tumour in a koi carp (Cyprinus carpio). Australian Vet J. 84(5):178–181.
5. Stegeman N, Heatley JJ, Rodrigues A, Pool R. 2010. Nephroblastoma in a koi (Cyprinus carpio). J Exotic Pet Med. 19(4):298–303.
6. Vergneau-Grosset C, Summa N, Rodriguez CO, Cenani A, Sheley MF, McCarthy MA, Tanner JC, Phillips KL, Hunt GB, Groff JM. 2016. Excision and subsequent treatment of a leiomyoma from the periventiduct of a koi (Cyprinus carpio koi). J Exotic Pet Med. 25(3):194–202.
7. Novelo ND, Tiersch TR. 2012. A review of the use of ultrasonography in fish reproduction. N Am J Aquac. 74(2):169–181.