Rapid growth of farmed cod in sea cages in the Faroe Islands

Abstract

The observed growth of cod in a farming trial in the Faroe Islands was compared to the predictions of a known cod-growth model for ambient sea temperatures in Norway, Iceland and the Faroe Islands. The growth was also compared to optimal growth rates (denoted as “optimal growth”), as predicted by the model. According to the model, the Faroese temperatures are most favorable for cod growth and closest to the optimal growth. Assuming a starting weight of 30g on 15 May, the model predicts growth to 4kg (round weight) in 667, 708, 778 and 896days for optimal, Faroese, Norwegian and Icelandic temperatures, respectively. The farming trial used semi-intensively produced juvenile cod from broodstock collected on the Faroe Bank. The on-growing was made in three commercial sea cages: Cage 1 with natural light, and Cages 2 and 3 with artificial underwater light to inhibit sexual maturation. At 836days post hatching, the mean weight of about 30 sampled fish from Cages 1, 2 and 3 was 2.95, 4.06, and 4.16kg, respectively. By determining the gonad weight of the sampled fish, the artificial light is shown to successfully delay sexual maturation in Cages 2 and 3 until 4kg body weight. The best economical feed conversion ratio and yield per stocked juvenile — estimated for Cage 3 — were about 1.2 and 4.0, respectively. Total accumulated mortality was about 20%. The realized growth data indicate that cod farming with rapid growth: 4kg in about 28months post hatching with controlled sexual maturation is possible in the near-optimal sea temperatures around the Faroe Islands. The stable sea temperature and the relatively low and stable ambient daylight during summer in Árnafjørður (62°15′N), Faroe Islands, which is further damped by the sea water above the underwater lights, are suggested to have assisted the control of the sexual maturation.