Ontogenetic change in preferred temperature and diel activity of the yellow bullhead, Ictalurus natalis

Abstract

1. 1. In an electronic thermoregulatory shuttlebox, the (24 hr) mean preferred temperature of 12 adult yellow bullheads was 27.6°C, while that of 12 juveniles was 28.8°C; the mean for all ages was 28.4°C (final preferenda). 2. 2. Mean preferred temperatures differed by no more than 0.4°C between photophase (day) and scotophase (night) of the light cycle. 3. 3. Adult bullheads were nocturnal (most active during the central 8 hr of the scotophase), while juveniles were more crepuscular (most active during the two 4-hr “dusk” periods centered about the light-dark and dark-light transitions).