Initial Mortality and Retention Associated with Using Passive Integrated Transponders in Black Crappies

Abstract

We assessed initial retention and mortality associated with using passive integrated transponders (PITs) for marking black crappies Pomoxis nigromaculatus by conducting 48-h net-pen trials (N = 4 trials) in April–May 2007 and one 14-d trial in October 2007. Black crappies (N = 175; total length (TL) range = 175–328 mm; mean TL = 265 mm; SE = 2.1 mm) were captured from a Minnesota lake by boat electrofishing or angling. Before being placed in the net-pen, each fish received one of four treatments: (1) a 12-mm PIT, (2) a left pectoral fin clip, (3) a PIT and a fin clip, and (4) no fin clip or PIT (i.e., reference fish). We injected PITs posterior to the pelvic girdle using a 12-gauge hypodermic needle. Average water temperature during trials ranged from 10.5°C to 16°C. No fish died and no PITs were shed during the 48-h trials. All PITs were retained during the 14-d trial in October, but 5 of the 42 black crappies died between days 12 and 14. None of the dead fish belonged to the PIT-only treatment. Mortality was probably the result of net-pen confinement, but four of the five mortalities had received a fin clip. Black crappies that retained PITs were filleted, and all PITs were observed to remain outside the typical range of meat removed by anglers for consumption. We conclude that PITs applied in this manner were initially safe (i.e., were not consumed in fillets), were effective (i.e., 100% retention), and did not increase initial mortality of black crappies at these water temperatures. Depending on fin regeneration rates, fin clips might serve as an effective secondary mark for assessing PIT retention in black crappies over certain periods of time, but mortality associated with fin-clipping should be assessed to ensure that mortality rates are low.