Effects of Handling on Oxygen Requirements of American Shad (Alosa sapidissima)

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Abstract
Oxygen tolerance was determined 0.25, 3, and 24 hr after introducing young American shad (Alosa sapidissima) to washtubs 7, 4, 2, 5, 2, and 2 days after previous disturbance in the holding tank. Dissolved oxygen at equilibrium loss and death varied from 1.1 to 8.0 and 0.9 to 5.7 mg/liter, respectively; and mean oxygen levels at equilibrium loss and death in the 3-hr × 2-day tests were 1.5–3 times higher than in any other handling combination. Present evidence indicates that the effects of handling American shad vary, with the intensity of excitement generated by handling seeming to determine whether the fish lives, dies immediately, or dies later. This phenomenon is probably responsible for difficulty in transporting and marking this species and for conflicting reports on oxygen requirements and salinity and low temperature tolerance. Mean oxygen levels with 99% confidence limits at equilibrium loss and death of unexcited individuals were 1.62 ± 0.13 and 1.28 ± 0.19 mg/liter, respectively. Virtually no individuals lost equilibrium or died until oxygen declined to 2.56 and 1.92 mg/liter, respectively. Nearly all lost equilibrium or died at 0.68 and 0.64 mg/liter, respectively. Field and laboratory evidence suggests that minimum daily oxygen levels of 2.5–3.0 mg/liter permit migration through polluted areas, but 4.0 mg/liter appears necessary in spawning areas.

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