An experimental study of cavitation damage on tissue of Carassius auratus in a jet fish pump

The jet fish pump is a potentially valuable tool for fish transport. Though jet fish pumps have been shown to cause the least damage to fish, cavitation as a commonly encountered flow phenomenon can lead to injury or death of fish. Experiments were conducted to investigate damage to tissue of Carassius auratus caused by different cavitation stages in a jet fish pump. Mortality was assessed for 48 h after the fish passed through the device. Tissues from swim bladders, livers and gills were examined. Fish were also examined for several important enzymes that are indicators of tissue injury. The results showed that cumulative mortalities of fish in cavitation operating conditions were higher than those in non-cavitation operating conditions at each sampling time. The cumulative mortality in the stable cavitation condition reached 55% within 48 h after the experiment. Two types of swim bladder damage, crumpling and rupturing, were found in 60% of the dead fish. The damage rate of swim bladders rose with the increase of cavitation, and broken swim bladders were found only in cavitation operating conditions. In addition, liver damage was found in those dead fish experiencing intensive cavitation operating conditions, and significantly high serum ALT and AST activity verified this damage. Free bubbles, an essential symptom of the gas bubble disease, were found in the gill filament of those fish experiencing intensive cavitation operating conditions. The significantly high serum LDH activity indicated that fish experienced intense anaerobic respiration during intensive cavitation operating conditions. Judging from the significant serum Cr content, cavitation in the jet fish pump also posed a potential risk for the kidneys of fish. Moreover, a pressure damage experiment showed that rupturing of swim bladders occurred in the recompression process; environmental pressure between 40 kPa and 58 kPa was a transition area for pressure damage to swim bladders in vitro. Swim bladders in vitro were safe when environmental pressure was above 58 kPa, yet they were broken when environmental pressure was less than 40 kPa. This study illustrates that intensive cavitation is a dangerous flow phenomenon for fish in a jet fish pump and should be avoided in practical applications.