© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Quality of Nephrops as food for Atlantic cod (Gadus morhua L.) with possible implications for fisheries management
a Marine Research Institute Skúlagata 4, PO Box 1390, 121 Reykjavík, Iceland
b Department of Biology, University of Iceland Grensásvegur 12, 108 Reykjavík, Iceland
*Correspondence to B. Björnsson: tel: + 354 552 0240; fax: + 354 562 3790. e-mail: bjornb{at}hafro.is.
Nephrops was found to be of low quality as food for cod. In a laboratory experiment the mean specific growth rate of 1 kg cod was 0.184 and 0.415% d–1 when fed to satiation on Nephrops and capelin, respectively. This large difference in growth rate resulted not only from less intake of Nephrops (1.19 kg cod–1) than capelin (1.55 kg cod–1) but also because more Nephrops (4.6 kg) than capelin (2.2 kg) were required to produce each kilogramme of cod. Higher food conversion ratio was consistent with lower fat content of Nephrops (1.3%) than capelin (9.2%) but the exoskeleton also reduced the digestion rate of Nephrops. In the groups where Nephrops and capelin of equal mean weight were offered simultaneously, 40% of the diet consisted of Nephrops during the first week and 10% during the final seven weeks of the experiment. At the end of the experiment, condition factor, liver index, and gonadosomatic index were significantly lower for cod fed on Nephrops (0.967, 5.7, 7.1, respectively) than for those fed on capelin (1.086, 15.8, 11.2, respectively). These results suggests that predation by cod on Nephrops might be reduced by regular release of capelin or other similar food in the distributional areas of Nephrops.
Keywords: cod, food quality, Nephrops, predator–prey, stock enhancement
Received 11 March 2003; accepted 1 June 2004.