Abdomen swollen
Lower body of fish is bloated and swollen to a considerable degree.
Tumourous growth on liver. If it manifests itself on many fish Suspect food inputs . Especially watch for pesticide contamination, or Aflatoxins.
Almost invariably fatal. Veterinary operation if fish is especially valuable.
Note. This appears to be a medical reference.
Notwithstanding it also refers to FISH studies and the similarities of some of the chromosomes, so it could be a good start to finding specific sequences on Fish.