Effects of combined exposure to elevated ammonia and low dissolved oxygen levels in greenlip (Haliotis laevigata Donovan) and blacklip (H. rubra Leach) abalone. 1. Growth and mortality data from simulated systems failure.

A growth trial was conducted on two Australian species of commercially cultured abalone to determine the effect of episodic exposure to sub-optimal water quality on growth and mortality. This was primarily designed to simulate systems failure, resulting in partial or complete interruption in the normal water exchange and corresponding changes in dissolved oxygen and ammonia levels. Experimental abalone were nominally exposed, at intervals ranging from once in six weeks to once a week, to 60% dissolved oxygen saturation and 150 microg/L un-ionised ammonia for 8 hours. No significant effect on growth or mortality was found for either species, with observation of abalone behaviour and food consumption indicating the exposures imposed a mild and transient stress. A more severe challenge exposure (nominally 30% dissolved oxygen and 600 microg/L un-ionised ammonia for 8 h) at the end of the growth trial had a greater impact on food consumption and activity, but this disappeared within 24 hours and did not cause any mortality after 2 d.