HEXAMITA INFECTION DURING A NUTRITIONAL TRIAL IN RAINBOW TROUT Oncorhynchus mykiss

This study reports an outbreak of Hexamitiasis in rainbow during a nutritional trial . Moribund and dead fish were subjected to sanitary control, such as microbiological and parasitological examination. Infection drastically reduced fish population within the experimental trial and 6 tanks resulted positive to hexamita infection. Th is study showed the necessity to perform effective sanitary control strategies during an experimental trial.

The use of fish in an experiment is complicated by various factors ,  since a ny sort of excessive stress can degrade the fish's health and allow the development of diseases , which can kill the fish or may confound research results. Hexamitosis is the most frequent flagellate internal parasitosis, reported in salmonids, cyprinid , ornamental species, and in several marine fish. Distribution cover a wide geographic range of cold, temperate and warm waters , in North America, Asia and Europe.  The aim of this study is to report an episode of Hexamitiasis in rainbow trout during a nutritional trial for highlight the importance of sanitary control.

The experimental system consisted of 24 fiberglass tanks of 400 L, artesian well water (constant temperature of 13 ± 1° C) was supplied in flow-through open system. Moribund and dead fish were subjected to sanitary control, such as microbiological and parasitological examination.  Entire contents of intestine were emptied, and each specimen was examined by light microscopy for the parasite presence. Hexamita if present, was scored ordinally: 0 (none), + (1-50 parasites), ++ (50-100 parasites), +++ (100< parasites) and ++++ (uncountable).

Hexamita infection drastically reduced fish population within the experimental trial, in fact 6 tanks resulted positive to  parasite

infection .  In every infected tank fish shows anorexia, melanosis and lethargic behavior. Infected fish shows a severe weight and length loss. In infected fish there was no food in the gastrointestinal tract, but  the presence of yellow mucus was significantly higher in infected fish. The score of Hexamita infestation of the 6 tanks analyzed are:

The knowledge of the sanitary condition of fish used in experimental trials is fundamental to develop effective sanitary control strategies. Most diseases can be prevented by starting with pathogen-free fish, clean water and uncrowded conditions.  Some studies have reported that pathological effects arise when the host is weakened by stress factors such as inappropriate diet, low oxygen content in the water, overcrowding and handling .  Therefore, it's important to always start during the experimental tests with fish in which the good state of healt has been proven and carry out an adequate acclimatization and quarantine period sufficient to eliminate any risk.