Cod diets and photoperiod in a recirculating tank system
Land based aquaculture allows farmers to control the light/dark cycle (photoperiod), which can have a significant effect on the growth and feed conversion efficiency of farmed fish. We studied the growth performance of juvenile Atlantic cod (Gadus morhua) reared under different photoperiods and three commercial diets.
Three RAS units were used to simultaneously test three feed/photoperiod regimes that might be encountered in the wild or aquaculture; LightDark (LD) 24:0, LD12:11 (+1 h crepuscular period) and LD6:6 (+12 h crepuscular periods). Feed was administered during the light period every 30 min for a 3 min feeding duration. In each RAS unit three diets (A, B and C) were tested, which were broadly similar in composition but from different manufacturers. Water exchange rate averaged 10-19% in the three recirculation systems, and key water quality parameters such as NH4+ and CO2 remained at low effect concentrations (<0.4 and <3 mg L-1, respectively). Final stocking densities were 45-60 kg m-³.
The figure below shows that there was a significant influence of both feed/photoperiod regime and diet on specific growth rate (SGR). Fish receiving the LD12:11 and LD6:6 regimes and Diet A grew best (SGR 2.59 and 2.54 % d-1 respectively). Fish fed Diet B and C also grew best under the LD12:11 and LD6:6 feed/photoperiod regimes (SGR range of 2.41 – 2.46 % d-1). Conversely, fish kept in the LD24:0 feed/photoperiod regime grew relatively slowly irrespective of diet type (SGR range of 2.26 – 2.32 % d-1). The feed conversion performance of the feed/photoperiod regimes and diets followed the same pattern.
This research has been published:
Fülberth, M., Moran, D., Jarlbæk, H., Støttrup, J.G., (2009). Growth of juvenile Atlantic cod Gadus morhua in land-based recirculation systems. Effects of feeding regime, photoperiod and diet. Aquaculture, 292: 225-231.
This research was led by M Fülberth as part of his MSc thesis. My participation in this project was made possible by a postdoc fellowship from the NZ Foundation for Research Science and Technology.