Behavioral Responses of Northern Pike, Yellow Perch and Bluegill to Oxygen Concentrations under Simulated Winterkill Conditions

Abstract

Northern pike (Esox lucius), yellow perch (Perca flavescens), and bluegill (Lepomis macrochirus), were exposed to successively lower oxygen concentrations 4.0, 2.0, 1.0, 0.5, and 0.25 mg/liter) each day for five days in aquaria sealed above with simulated ice. Water temperature varied from 2.5 to 4.0 C and light intensity and photoperiod simulated conditions in an ice-covered lake. Gill ventilation rates increased in response to lowered oxygen, doubling for bluegill and yellow perch but quadrupling for northern pike. Maximum ventilation rates occurred at 0.5 mg/liter D.O. for northern pike and yellow perch and at 1.0 mg/liter D.O. for bluegill. Locomotory activity was greatest at 0.25 mg/liter D.O. for northern pike but at 0.5 mg/liter D.O. for yellow perch and bluegill. Northern pike and yellow perch began to move toward the ice at 0.5 mg/liter D.O. At 1.0 mg/liter D.O., bluegill kept sinking to the bottom of the aquaria; they continually made forays upward only to sink again. Northern pike and yellow perch nosed at the under surface of the ice at the lowest oxygen concentrations while bluegill seldom did. The fish never aggregated more than 10 percent of the time even at the lowest concentrations of dissolved oxygen. Almost all northern pike and yellow perch were still alive at 0.25 mg/liter D.O. while all bluegill were dead. Evidently northern pike are best adapted for survival in winterkill lakes and bluegill the least. The upward movement takes the fish to the highest oxygen available in the immediate vicinity. Detection of an oxygen gradient is not a requirement of this response because in the aquaria the fish move to the ice at low oxygen concentrations in absence of a gradient. High free CO2 and dissolved H2S are also not necessary to stimulate or orient the upward movement. Increased locomotory activity, if coupled to reduced activity when respiratory distress is alleviated, also provides an effective mechanism for locating higher oxygen. The increases in gill ventilation have obvious survival value.