As the koi hobby grows and the need for expanded specialized veterinary care becomes evident, more diagnostic procedures are needed. Here is an example of researchers using endoscopic evaluation on koi.
 

Abstract
OBJECTIVE To describe a technique for endoscopic evaluation of the coelomic viscera of koi (Cyprinus carpio) and to evaluate the ability to visually examine coelomic structures by use of an approach cranial or caudal to the pelvic girdle.
RESULTS The coelioscopic procedure was tolerated well, and all koi recovered uneventfully. For all fish, ease of entry and visual examination scores of the liver, intestines, gonads, heart, and anterior kidney were satisfactory to excellent. Visual examination of the posterior kidney and swim bladder was satisfactory to difficult, whereas the spleen and gallbladder were not visually identified. No significant differences were noted in entry or visual examination scores between the cranial and caudal approaches or between sexes. Minor complications included mild hemorrhage, rupture of the gonadal capsule, formation of adhesions between the viscera and incision site, and delayed healing of the incision.
CONCLUSIONS AND CLINICAL RELEVANCE Diagnostic coelioscopy of koi appeared to be safe and effective. This procedure could have potential for use in examination of coelomic structures and disease diagnosis.
 
https://avmajournals.avma.org/view/journals/ajvr/80/3/ajvr.80.3.221.xml