Goldfish Carassius auratus

Goldfish is an East Asian cyprinid, native to China and Japan and introduced almost everywhere, kept and bred for colour rather than for food; it is the ornamental species a companion-animal practice actually sees. Farmed fish are produced in outdoor ponds and are generally under 100 mm, spawned by broadcasting eggs over gravel, plants or woody debris in aggregations with no parental care, females releasing three to ten batches at eight- to ten-day intervals. Wild-type maxima are far larger: FishBase records 48 cm total length, 1.6 kg and a maximum reported age of 41 years, with tolerance from 0 to 41 degrees C and pH 6.0 to 8.0, which is why a neglected pond fish can outlive the owner's expectations. Two points matter clinically. Goldfish can be infected by koi herpesvirus and pass it to koi without showing disease signs, so a mixed goldfish-and-koi pond is an infection risk that looks perfectly healthy. And Argulus, the fish louse, is commonest in goldfish and koi, causing pinpoint haemorrhage, scale loss and secondary infection and carrying spring viraemia of carp, with no FDA-approved treatment. Being an ectotherm, the fish's metabolism and drug handling follow pond temperature.