EFFECTS ON TEMPERATURE ON SPONTANEOUS AND THYROXINE-STIMULATED LOCOMOTOR-ACTIVITY OF ATLANTIC COD

Spontaneous locomotor activity of cod Gadus morhua maintained at 6 deg rees C tripled from February to May. In contrast, locomotor activity o f cod held at 2 degrees C was significantly lower than at 6 degrees C (between 25 and 65% lower) and the seasonal increase was smaller. Plas ma levels of both thyroxine (T-4) and triiodothyronine (T-3) did not d iffer between 2 and 6 degrees C. T-4 injection increased locomotor act ivity by 10% for both temperature regimes. These data indicate that lo w water temperature reduces locomotor activity associated with migrati on in cod and that thyroid hormones are not involved in this decrease. This study provides a possible mechanism through which cold waters ma y affect migration and distribution of cod via its effects on locomoto r activity and swimming speed. (C) 1998 The Fisheries Society of the B ritish Isles.