L Journal of Experimental Marine Biology and Ecology 242 (1999) 201–210 www.elsevier.nl / locate / jembe Temperature dependency of early growth of turbot ( Scophthalmus maximus L.) and its implications for developmental progress a, b a * F.-A. Weltzien , M. Planas , H.J. Fyhn a ´ Department of Zoology, University of Bergen, Allegt. 41, N-5007 Bergen, Norway b Instituto de Investigaciones Marinas C.S.I.C., Eduardo Cabello 6, E-36208 Vigo, Spain Received 21 January 1999; received in revised form 28 May 1999; accepted 7 July 1999 Abstract Growth in developing turbot larvae can be expressed independently of temperature when using effective day-degrees ( D8 ) as an index of development. The calculation of D8 is based on the eff eff principle of thermal summation whereby the rate of development is linearly related to the ambient temperature above a species-specific threshold temperature ( T ) at which development is 0 theoretically arrested. The T for turbot embryos is 5.38C. The increase in wet body mass of 0 developing turbot larvae at 14, 18, and 228C can be aligned into a single exponential relationship regardless of incubation temperature when using D8 as the index of development. Previous eff attempts to relate physiological processes in poikilothermic animals, including fish, to incubation temperature are discussed.  1999 Elsevier Science B.V. All rights reserved. Keywords: Development; Effective day-degrees; Poikilotherms; Temperature effects; Turbot (Scophthalmus maximus L.) 1. Introduction The duration of any developmental period in a poikilotherm, measured in chronologi- cal time units (e.g. days), is closely related to temperature; increasing with lower temperatures and decreasing with higher temperatures. Within a tolerable temperature range, an organism can carry out normal activities although the ambient temperature exerts a major influence on the pace of various biological processes (Fry, 1947). A *Corresponding author. Present address: Institute of Marine Research, Austevoll Aquaculture Research Station, N-5392 Storebø, Norway. Tel.: 147-56-180-342; fax: 147-56-180-398. E-mail address: finn-arne.weltzien@imr.no (F.-A. Weltzien) 0022-0981 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0022-0981(99)00099-4