Growth and survival of Arcto-Norwegian and Norwegian coastal cod larvae (Gadus morhua L.) reared together in mesocosms under different light regimes

To evaluate genetic differences in growth and survival potential as a funct ion of light regime, cod larvae from two stocks (CC: coastal cod and AC: Ar cto-Norwegian cod, spawning at latitudes of 60 degreesN and 69 degreesN res pectively) were co-reared in mesocosms, The experiment was carried out with two artificially illuminated light regimes, corresponding to the natural p hotoperiod at peak spawning of the respective stocks (CC: 7-8 h distinct da rk period, AC: 'mid-night sun' as continuous light with 2-3 h reduced light intensity). One additional regime with ambient natural light analogous to 60 degreesN was used. At termination on day 36 post-hatch, larvae of the co -reared stocks were distinguished from each other by a genetic marker in th e CC stock. Stock-specific differences in growth rate and survival were ind icated, with CC larvae growing and surviving better than AC larvae. This is in agreement with earlier comparisons of larval growth in these stocks. Th e 69 degreesN light regime did not enhance growth for any of the two stocks . However, natural light greatly increased growth rate of both stocks, indi cating important mechanisms in regulation of larval feeding relative to lig ht quality or intensity. The results may be important for choice of stock a nd illumination in intensive aquaculture of this species.