PROTEIN-SYNTHESIS AND GROWTH IN JUVENILE ATLANTIC HALIBUT, HIPPOGLOSSUS-HIPPOGLOSSUS (L) - APPLICATION OF N-15 STABLE-ISOTOPE TRACER

The growth efficiency of juvenile Atlantic halibut, Hippoglossus hippo glossus (L.), was investigated by comparing wet weight specific growth rates (SGRs) over 28 days with protein synthesis rates measured using a non-invasive stable isotope (N-15) tracer technique. A diet contain ing N-15-labelled protein was fed at a single meal and individual feed intake was measured by X-ray radiography to allow calculation of the amount of N-15 consumed, Excreted ammonia and urea were collected from each fish and the ratio of N-15 to N-14 was used to calculate rates o f protein synthesis. Peak rates of ammonia excretion occurred 12 h pos t-feeding, Rates of urea excretion did not change after feeding and re mained relatively constant over the 48-h measurement period, Urea acco unted for 17% of the measured nitrogen excretion and showed no enrichm ent with N-15. Mean protein growth rates were 1.31 +/- 0.06% day(-1), while whole animal fractional rates of protein synthesis were 2.02 +/- 0.24% day(-1). The mean protein synthesis retention efficiency was 77 .41 +/- 9.09%, which is higher than that recorded for most other teleo sts, This suggests that halibut have a relatively low cost, high growt h efficiency growth strategy.