Growth model for Atlantic cod (Gadus morhua): Effects of temperature and body weight on growth rate Björn Björnsson a, ⁎ , Agnar Steinarsson b , Tómas Árnason c a Marine Research Institute, Skúlagata 4, P.O. Box 1390, 121 Reykjavík, Iceland b Marine Research Institute, P.O. Box 42, 240 Grindavík, Iceland c University of Akureyri, Borgir v/Nordurslód, 600 Akureyri, Iceland Received 10 April 2007; received in revised form 20 June 2007; accepted 20 June 2007 Abstract Results from several laboratory experiments showed that at each temperature there was a linear relationship between the logarithms of specific growth rate (G%/day) and body weight (W g) of Atlantic cod fed to satiation: lnG = α + βlnW. Both α and β were found to be a function of temperature (T °C): α = a + bT + cT 2 ; β = d + eT; a = - 0.7620, b = 0.3982, c = - 0.0128, d = - 0.1500, e = - 0.0239. The e-parameter was altered by 10% from the laboratory value (to e = - 0.0215) to tune the model in accordance with growth rate of large cod reared in sea cages in Norway. The model predicts that the optimal temperature for growth (T opt.G ) declines with body weight: T opt.G = 15.57–0.8426lnW, i.e. 15.0, 13.0, 11.1 and 9.2 °C for 2, 20, 200 and 2000 g fish, respectively. The predicted growth rates at optimal temperature (G max ) were 7.41, 2.62, 1.02 and 0.44%/day for 2, 20, 200 and 2000 g fish, respectively. Model calculations show that 30 g cod juveniles stocked in sea cages on 15 May have reached 1.6 and 2.1 kg by the end of the second year and 4.6 and 6.3 kg by the end of the third year, in Northwest Iceland and West Norway, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: Atlantic cod; Cod farming; Growth experiments; Growth model; Optimal temperature 1. Introduction In recent years, interest in farming of cod (Gadus morhua) has been growing, especially in Norway, Iceland, Scotland, Faroe Islands and Canada. Juveniles are being produced year-round in hatcheries, selective breeding is underway and vaccines are being developed (Björnsson, in press). There is a large demand for farmed cod to fill the gap between increasing demand and diminishing supply from the cod fishery. It has been predicted that the production of farmed cod will reach a similar level as that of Atlantic salmon (Salmo salar) within the next 15–20 years (Rosenlund and Skretting, 2006). The price of cod is only moderate and therefore it is crucial to minimize the production costs in cod farming. Temperature is one of the most important environmental parameters determining the growth potential of cod (Jobling, 1988; Brander, 1994; Björnsson et al., 2001) and the optimal temperature for growth has been found to decrease with increasing weight of cod (Björnsson et al., 2001). Up to a certain size the juveniles must be reared in land-based farms where optimal temperatures can be maintained but for the rest of the life-cycle cod have to be reared in sea pens at ambient temperature. Aquaculture 271 (2007) 216 – 226 www.elsevier.com/locate/aqua-online ⁎ Corresponding author. Tel.: +354 575 2045; fax: +354 575 2001. E-mail address: bjornb@hafro.is (B. Björnsson). 0044-8486/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2007.06.026