Capture-induced exertional rhabdomyolysis in the Shortfin Mako Shark, Isurus oxyrinchus

Shortfin Mako sharks (Isurus oxyrinchus) are top-order predators in oceanic food chains. They are captured worldwide by commercial and recreational fisheries, but little is known about the effects that fishing has on the homeostasis and longevity of these animals.

This study aimed to assess the health of Shortfin Mako sharks captured by recreational fishers off eastern Australia.

Twenty-four sharks were captured, and their gender, length, weight, reproductive maturity, and stage were recorded. After blood and urine collection, serum analytes were quantified using standard biochemical methods, whereas urine was analyzed using semi-quantitative reagent strips, microscopic examination, centrifugation, and ammonium sulfate precipitation tests.

Six Makos presented with red-brown urine. The means of notable serum analytes were as follows: sodium 276 mmol/L, potassium 15.6 mmol/L, inorganic phosphate 10.6 mmol/L, magnesium 3.3 mmol/L, urea 325 mmol/L, creatinine 52 μmol/L, AST 2806 U/L, CK 240938 U/L, lactate 44.4 mmol/L, osmolarity 1160 mmol/L, and pH 7.13. These analytes differed from the respective sand tiger shark reference interval, which was used as a proxy for Makos. The red-brown urine was due to myoglobin and had a mean pH of 5.76 that, when combined with red-brown casts, led to a diagnosis of fishing-induced exertional rhabdomyolysis that occurred secondary to lactic acidosis, hypoxia, and hypovolemia. It was further exacerbated by hyperkalemia and acute renal failure, serious complications that often lead to mortality.

Practitioners caring for sharks and rays should consider collecting urine from free-living or aquarium animals when they are captured for examination and/or treatment, particularly at times with maximal seawater temperatures.