Communications: Responses of Northern, Florida, and Hybrid Largemouth Bass to Low Temperature and Low Dissolved Oxygen

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Abstract
Two parental subspecies of largemouth bass (Micropterus salmoides), northern (M. s. salmoides) and Florida (M. s. foridanus), and their reciprocal F1 hybrids were examined for their responses to low temperature and low dissolved oxygen concentrations. The four strains (verified electrophoretically) survived a temperature decrease from 21 to 1°C at a rate of about 1°C/d followed by immediate warming. Among fish maintained at low temperature (2.0 ± 0.4°C; mean ± SE) for 5 d, mortalities were 48% for the Florida fish and 4–5% for the Florida (female) hybrid, compared with zero for the northern fish and the northern (female) hybrid. All four groups showed similar trends in feeding behavior during the temperature treatments. At 22°C acclimation, the residual oxygen concentrations (oxygen concentrations at time of death by hypoxia, during sealed-jar-hypoxia bioassays) were lower in tests with the northern and Florida subspecies than in tests with the hybrids, and were lower for northern than for Florid...