Food selection and digestion characteristics of Atlantic halibut ( Hippoglossus hippoglossus) larvae fed cultivated prey organisms

Abstract

The aim of the present study was to investigate the pattern of food selection by larvae of Atlantic halibut fed Brachionus plicatilis and different size classes of Artemia franciscana, including short-term enriched (ST) A. franciscana nauplii. A second aim was to study the digestibility of different size classes of A. franciscana by halibut larvae. The larvae did not show any significant preference for B. plicatilis or nauplii of A. franciscana during the first 2 days after initiating first feeding at 285 day degrees. From day 3 and onwards, they selected significantly ( P<0.05) for A. franciscana. When offered different size classes of A. franciscana, from newly hatched nauplii to juveniles as long as 4.8 mm, they selected positively for newly hatched A. franciscana (<0.60 mm) up to day 20 (3.0–3.5 mg dry weight larva −1), when they suddenly started to select positively for larger A. franciscana. From the larval dry weight of 4.0 mg (after day 20), they selected significantly for A. franciscana in the size class 1.20–1.39 mm. However, the larvae ingested A. franciscana shorter than 0.60 mm during the whole live feed period, independently of the availability of larger prey items. The ST A. franciscana nauplii, which is the most commonly used live feed size for halibut larvae, was apparently slightly less digested than the other size classes. It is suggested that this difference in digestion ability was a result of the very high lipid content of the ST A. franciscana compared to that of juvenile A. franciscana and newly hatched A. franciscana. Based on the selection and digestibility results the feeding regime for halibut larvae should consist of newly hatched nauplii, eventually together with B. plicatilis, the first week. Thereafter two weeks with ST A. franciscana nauplii and then a switch to 3-day-old A. franciscana juveniles for the rest of the live feed period.