Short- and long-term differences in growth, feed conversion efficiency and deformities in juvenile Atlantic cod (Gadus morhua) startfed on rotifers or zooplankton

Growth, feed conversion e⁄ciency and frequencies of skeletal deformities were studied in juvenile Atlantic cod (Gadus morhua )t hat had been startfed on either rotifers (rotifer group) or zooplankton (zooplankton group). After metamorphosis, the ¢sh were reared at four constant temperatures (7, 10, 13, 161C) or moved successively from 16 to 13 and 101C (T-step, average 13.2 1C). The zooplankton group had a consistently higher growth rate at all the temperatures studied. Further, the zooplankton group had higher food intake (20%) and higher feed conversion ratio (1.65 vs. 1.31). In addition, a signi¢cantly higher incidence of skeletal deformities was found in the rotifer group (14.2%) compared with the zooplankton group (4.1%). After termination of the laboratory study, the ¢sh were reared in sea pens under ambient conditions for 17 months. Final weights of the zooplankton group were consistently larger (between 12% and 14% larger depending on original temperature groups). To verify the growth results, we conducted a follow-up study where a single egg group was divided into two parts and fed either on rotifers or zooplankton. This study indicated similar growth diierences as found in the ¢rst study. Overall, our data suggest that diierent startfeeding diets may be important for long-term growth, incidence of deformities and quality of juvenile cod. The use of zooplankton can greatly improve long-term growth and quality of cod juveniles. The study also highlights the advantage of using elevated temperatures in the juvenile phase as this will lead to signi¢cantly higher ¢nal weights in the adult stage.