ASPHYXIA IN FARMED FISH AND APPLICATION OF ANTI-ASPHYXIA MEASURES

Objective: Sudden fish death is an often incident in hatcheries and fish rearing tanks. Such cases are caused by a decrease or increase in the concentration of certain dissolved gases in the rearing water leading to death due to asphyxia. In particular, the causes are attributed to the reduction or stop of the water flow, malfunction of the aerating or oxygenating or water degasing systems and wrong assessment of the number of reared fish, in correlation to their age/size. In our study, we described the clinical and pathology findings of asphyxia in fish and developed anti-asphyxia measures. Method & Materials: In two rearing tanks containing fifty sea breams (Sparus auratus) per tank the water supply was stopped until fish showed asphyxia. 5 fish were sampled from each tank. The remaining 45 individuals of the first tank were transferred to another tank containing clear water supersaturated with oxygen. To the 45 individuals of the second tank, serving as a control group, only clear water was supplied in their tank. Medical treatment was applied only to the first group and both fish groups were kept in the rearing tanks for a period of 30 successive days. Blood and fish tissues were examined. Results & Conclusion: The developing asphyxia in fish is characterized by the rupture of the gill capillary vessels and the destruction of the cell membranes in the respiratory epithelium, resulting in the reduction of the respiratory surface and the progressive aggravation of the respiratory process. The fish showed a decline of haematopoiesis and the consequent reduction in their immunoreactive capacity. The direct result of the above injuries and disorders was the blood loss via the gills, the reduced supply of oxygen for the tissues, and the gradual necrosis of the respiratory epithelium with the consequent establishment of local infections. In severe cases, the death of the fish is the common result. In our experiment, we induced asphyxia to two groups of fish, examined the health of the fish in the days followed and described the measures that should be immediately applied to the fish minimizing the incidence of death and the risk of an infection due to the induced stress to the farmed fish population. These measures include the transfer of the fish in another tank filled with clear supersaturated with oxygen water, the bath of the recovered fish with a disinfectant agent and the further treatment of the individuals with medicated feed.

کلیدواژه ها:

asphyxia ، anti-asphyxia measures ، oxygen ، carbon dioxide ، aquaculture