NORWAY - Unlike other fry, cod stock grows quicker when it is fed in the dark, says new research findings published at the Nofima show.
It is normal for fish farmers to feed fry in light conditions, as studies of a host of species, including salmon, have shown that fry grow best when they receive lots of light.
Research with cod larva show it too is reliant on light to eat and grow. However, no investigations have been carried out on whether the same effect is achieved with cod fry.
Senior Scientist Sten Siikavuopio at Nofima (formerly Fiskeriforskning) carriedout trials with three groups of juvenile cod to study how much the juvenile cod eat and grow when fed in light and dark conditions respectively.
New knowledge opens the way for more flexible feeding methods for cod fry.
All the juvenile cod received 12 hours of light conditions and 12 hours of dark conditions a day for a six-month period. The first group was fed when it was both light and dark, the second group only during light hours and the third group only during dark hours. The water temperature was 12 °C.
At the start of the trial, the fry weighed five grams. At the conclusion of the trial, they weighed around 90 grams, with no significant weight difference between the three groups. However, the scientists observed a tendency that the juvenile cod fed in the dark were a little larger than the other cod.
"This shows that the light conditions for juvenile cod are not of great significance," says Siikavuopio, adding that the findings open the way for more flexible methods for feeding juvenile cod.
The findings also indicate that the need to see food changes in the transition from cod larvae to juvenile cod. The scientists still do not have knowledge about how the cod eat in the dark. Do they eat as the feed is falling or do they find it on the tank bottom?
"This would be interesting to find out, especially with respect to whether this knowledge can be transferred to cod in cages, where the fish are reliant on eating the feed as it is falling," says Siikavuopio.