Ontogenetic changes in temperature preference of Atlantic cod

Final thermal preferendum (T) experiments were conducted in a horizontal thermal gradient tank from the beginning of August 2001 to mid-November 2001 using Atlantic cod Gadus morhua from 6(.)5 to 79(.)0 cut fork length (L-F). The value of T varied significantly (P < 0(.)005) with L-F (T= 7(.)23-0(.)054L(F)), with smaller (younger) fish choosing higher temperatures than larger (older) fish. The preferendum varied from 6(.)9degrees C for fish of 6(.)5cm to 3(.)0degrees C for those of 79(.)0cm. Experiments comparing fish positions in the gradient tank between thermal gradients of 0(.)5-11(.)0 and 4(.)5-14(.)5degrees C demonstrated that fish positions were determined by temperature selection instead of undesirable tank effects. This study is the first to demonstrate the effect of ontogeny on temperature preferences of a marine fish species. (C) 2005 Minister of Public Works and Government Services Canada.