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

Abstract

Growth, feed conversion efficiency and frequencies of skeletal deformities were studied in juvenile Atlantic cod (Gadus morhua) that had been startfed on either rotifers (rotifer group) or zooplankton (zooplankton group). After metamorphosis, the fish were reared at four constant temperatures (7, 10, 13, 16°C) or moved successively from 16 to 13 and 10°C (T-step, average 13.2°C). 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 significantly 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 fish 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 differences as found in the first study. Overall, our data suggest that different 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 significantly higher final weights in the adult stage.