How does induced polyploidy affect the swimming and physiological performance of juvenile sterlet (Acipenser ruthenus) and Siberian sturgeon (Acipenser baerii) and their reciprocal hybrids?

Spontaneous triploidization has been widely documented in cultured populations of many sturgeon species and the evidence of its occurrence in the wild has also been provided. We compared the critical swimming speed (Ucrit) of nine-month-old normoploid and triploidized individuals (obtained from normal fertilization or from normal fertilization followed by induction of the second polar body retention, respectively) of sterlet (Acipenser ruthenus), Siberian sturgeon (Acipenser baerii), and their reciprocal hybrids. Moreover, we assessed the primary haematological indices (blood haemoglobin concentration, Hb; haematocrit, PCV; erythrocyte count, RBC count), secondary haematological indices (mean erythrocyte volume, MEV; mean erythrocyte haemoglobin, MEH; mean erythrocytic haemoglobin concentration, MEHC) and plasma/serum chemistry (cortisol, osmolality and glucose) of both non-exercised and exercised sturgeons to investigate the ploidy-related differences. We found that in both purebreds and hybrids, triploidized sturgeons exhibited the same absolute and corrected Ucrit as normoploids. Triploidized sturgeons had lower RBC counts and larger erythrocytes with more haemoglobin than normoploids, but the increase in ploidy did not affect Hb, PCV, MEHC, plasma cortisol, plasma osmolality or serum glucose, except for the greater PCV in triploidized sterlet × Siberian sturgeon and higher levels of serum glucose in triploidized Siberian sturgeon × sterlet than in normoploids of the same hybrids. The magnitudes of exercise-induced changes in the inspected parameters were consistent between normoploid and triploidized populations. We conclude that juvenile triploidized sterlet, Siberian sturgeon, sterlet × Siberian sturgeon and Siberian sturgeon × sterlet were able to fully compensate for having fewer erythrocytes in their Hb and PCV and had the same oxygen carrying capacity as normoploids. Moreover, the magnitude of haematological and blood chemistry responses to exhaustive exercise did not differ between normoploid and triploidized sturgeons, and triploidization did not result in altered swimming performance.