23. (1) Where a discharger is required by this section to perform a rainbow trout acute lethality test, the discharger shall perform the test according to the procedures described in the Environment Canada publication entitled “Biological Test Method: Reference Method for Determining Acute Lethality of Effluents to Rainbow Trout”, as amended from time to time.  O. Reg. 233/07, s. 5. (2) Each rainbow trout acute lethality test required by this section shall be carried out as a single concentration test using 100 per cent effluent.  O. Reg. 760/93, s. 23 (2). (3) On one day in each month, on a day on which samples are picked up at the plant under subsection 19 (1), each discharger shall collect and immediately pick up a grab sample at each process effluent sampling point at the discharger’s plant and shall perform a rainbow trout acute lethality test on each sample.  O. Reg. 760/93, s. 23 (3). (4) There shall be an interval of at least fifteen days between successive pick-up days at the plant under subsection (3).  O. Reg. 760/93, s. 23 (4). (5) All samples picked up under subsection (3) in a month shall be picked up on the same day in the month.  O. Reg. 760/93, s. 23 (5). (6) Where a discharger has performed tests under subsection (3) for twelve consecutive months on samples collected from the same sampling point and the mortality of the rainbow trout in each test did not exceed 50 per cent, the discharger is relieved of the obligations under subsection (3) relating to the sampling point and shall instead collect and immediately pick up a grab sample at the sampling point on one day in each quarter and perform a rainbow trout acute lethality test on each sample.  O. Reg. 760/93, s. 23 (6). (7) Samples picked up at a plant under subsection (6) shall be picked up on a day on which samples are picked up at the plant under subsection (3).  O. Reg. 760/93, s. 23 (7). (8) If no samples are being picked up at a plant under subsection (3) during a quarter, samples picked up at the plant during the quarter under subsection (6) shall be picked up on a day on which samples are picked up at the plant under subsection 19 (1).  O. Reg. 760/93, s. 23 (8). (9) There shall be an interval of at least forty-five days between successive pick-up days at the plant under subsection (6).  O. Reg. 760/93, s. 23 (9). (10) All samples picked up under subsection (6) in a quarter shall be picked up on the same day in the quarter.  O. Reg. 760/93, s. 23 (10). (11) If a rainbow trout acute lethality test performed under subsection (6) on any sample from a sampling point results in mortality of more than 50 per cent of the test rainbow trout, subsections (6) to (10) cease to apply in respect to samples from that sampling point, and a discharger shall instead comply with the requirements of subsection (3) relating to the sampling point, until the tests performed under subsection (3) on all samples collected from the sampling point for a further twelve consecutive months result in mortality for no more than 50 per cent of the rainbow trout for each test.  O. Reg. 760/93, s. 23 (11). (12) A discharger shall notify the Director in writing of any change in the frequency of acute lethality testing under this Regulation at the discharger’s plant, within thirty days after the day on which the change begins.  O. Reg. 760/93, s. 23 (12). (13), (14) Revoked:  O. Reg. 760/93, s. 23 (15). (15) Spent:  O. Reg. 760/93, s. 23 (15). (16) Subsections (2) to (15) apply with necessary modifications to each cooling water effluent sampling point and, for the purpose, the reference in subsection (3) to each process effluent sampling point shall be deemed to be a reference to each cooling water effluent sampling point and the reference in subsections (3) and (8) to subsection 19 (1) shall be deemed to be a reference to subsection 26 (1).  O. Reg. 760/93, s. 23 (16). Monitoring — Acute Lethality Testing — Daphnia magna