The influence of temperature on the formation of zones in scales and otoliths of young cod

Abstract

From 27th October 1954 to 23rd February 1955 0-group cod from\nthe littoral region at Flødevigen were kept in aquaria, and furnished\nwith running sea-water of different temperatures:\nA: The temperature was normal for the season. It varied between\n14.3° C at the start, to 2.6° C on 20th February.\nIn the other experiments the temperatures were lowered within\na few days, and later kept constant:\nB: At 4° C.\nC: At S° C\nD: At 12° C.\n\nThe individual length increment varied within wide limits in all\nexperiments. The cause of the variations may tentatively be ascribed\nto different races being involved in the material collected.\nThe length attained in all experiments (tab. I), was of the same\norder as that normally found in nature, and there was no considerable\ndifference between codlings kept at different temperatures.\nAt the start in September 1954 the scales showed narrow sclerites\nnear the margin. A zone was forming. When the codlings were killed\non 23rd February 1955 the scales of the smallest individuals still had\nnarrow sclerites at the margin - irrespective of temperature. The\nmedium and large individuals in all experiments except at 12° C\nhad a wide space of large sclerites. At 12° C the sclerites were small\nor moderate, irrespective of quick growth.\nWe may draw the following conclusions:\na. Narrow sclerites are formed when the sea-temperature is high.\nb. Narrow sclerites are also formed at low temperatures i slow-growing\nindividuals.\nc. Wide sclerites are formed at low temperatures in medium and\nquick growers.\nThe results - as to the season of the formation of zones - are\nin full conformity with those referred to fromi nature.\nIt is evident, however, that narrow sclerites cannot be used as an\nindication of slow growth of the fish.\nThere seems to be a chance of correspondence between wide\nsclerites and quick growth. But quick growth at relatively high temperatures\nmay be associated with narrow sclerites.\nIn slow growers small sclerites will be predominant.\nThe otoliths were quite normal in cod at winter-temperature and\n4° C. There is an opaque centre, and a transparent zone surrounded\nby an opaque zone. At 8° C the transparent zone was generally more\ndiffuse and not so well marked. At 12° C the transparent zone seemed\nto proceed more or less diffuse to the margin of the otolith.\nThis indicates that the transparent zone is formed at relatively\nhigh temperatures, the opaque zone at relatively low. This is in\naccordance with the results arrived at by examining young cod from\nnature (Dannevig 1933).\nChemical analysis revealed that the formation of organic-opaque\nmaterial was highest at 4° C.\nThe results of the experiments indicate that the formation of zones\nin the scales and otoliths of the cod is influenced by temperature\ndirectly or indirectly.\nTo what degree other factors - food, light or an inherited rhythm\n- also come into the probleim will be discussed on the basis of further\nexperiments.