Posted: Monday 21 September 2009
The use of light technologies in the ongrowing of Cod (Gadus morhua)
Puberty is a major bottleneck during the on-growing of Atlantic cod, and although photoperiod manipulation (constant lighting) is already used to control sexual maturation within the industry, results to date are not fully successful. A better understanding of the cod's light sensitivity is therefore required to refine the use of light regimes. Aiming to address this issue, Mairi Cowan, a PhD student from the Institute of Aquaculture, supervised by Dr Herve Migaud and Dr Andrew Davie has carried out two tank studies at the Machrihanish marine laboratory facilities.
Effects of constant lighting on the welfare of Atlantic cod
In an attempt to make the response to photoperiod management more consistent in cod farming, new narrow wavelength technologies and increasing light intensities are being used however the potential welfare impacts of such illumination have not yet been well studied. 
This trial investigated the impact of traditional metal halide and novel green cathode lighting on the welfare and light sensitivity of Atlantic cod. Light treatments mimicked light exposure in an open cage system within 1.5 m of a light unit. As a whole, results clearly indicated that these lighting treatments had no chronic effects on welfare (stress response, immune function, retinal morphology and feeding activity). These findings have promising implications for the farming industry which is more widely favouring the use of narrow wavelength high intensity artificial lighting conditions.
Effects of shading in conjunction with constant green cathode lighting on sexual maturation of Atlantic cod
Photoperiod management of cod in enclosed tank systems is effective however, in the cage environment it has not been fully successful to date resulting at best in a 4 month delay. It is thought that this is due to the cod's acute perception of the overlying ambient photoperiod (i.e. perception of day/night differences). This trial investigated the effectiveness of shading (suppression of daylight) in addition to constant lighting for the prevention of maturation in cod reared outdoors. Results were very promising and indicated that maturation can indeed be inhibited in outdoor tanks (oocytes remained immature, gonadosomatic index, testosterone and 17β-estradiol remained at basal levels) through the use of outdoor shading treatments of 70% and 94%. These results are important and suggest that early maturation in cod can be suppressed in outdoor conditions by reducing the day/night light intensity signal and optimising lighting fields within the rearing unit. Further development and testing of the shading and lighting technologies in commercial set ups is now required.
This work was supported by SARF (Scottish Aquaculture Research Forum), the British Marine Finfish Association, Crown Estate, HIE (Highland and Island Enterprise) and Intravision Aqua AS.