| dc.description.abstract | In April 1982 cod larvae were reared in four 30 l laboratory
tanks and in two 300,000 l columnar plastic enclosures for 3-4
weeks from hatching. North Sea oil "production water" was added
to one of the enclosures immediately after introduction of the
yolk sac larvae. Natural zooplankton at an initial copepod
nauplii concentration of 5-7 l^-1 provided the food source for
enclosure larvae. Food in the tanks, mainly copepod nauplii and
small copepodites, was maintained at about 300 items 1^-1.
Post yolk sac specific growth rates of larvae in the enclosures
were 10.0% and 10.4% d^-1. In the laboratory, cod
larvae of Norwegian origin grew at 7.8% and 7.7% d^-1, while
those of Clyde Sea origin grew at 1.7% and 6.0% d^-1. Natural
daily mortality rates were 8.4% and 9.7% in the enclosures and
10.6%, 14.5%, 15.6% and 10.0% in the tanks. 'Production water '
had no detectable effect on the treated larvae.
Larvae in both systems started feeding at 4-5 days after
hatching and feeding incidence was soon over 60%. The diet of
enclosure larve consisted almost entirely of nauplii of the
copepod Pseudocalanus elongatus. The relationship between
numbers and sizes of food items relative to standard length and
the relarionship of maximum gut content weight to larval size
were determined. Pump samples revealed that cod larvae in the
enclosures preferred the top 7.5 m of the water column. | en |
