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

The aim of the present study was to investigate the pattern of food selecti on by larvae of Atlantic halibut fed Brachionus plicatilis and different si ze classes of Artemia franciscana, including short-term enriched (ST) A. fr anciscana 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 d uring the first 2 days after initiating first feeding at 285 day degrees. F rom day 3 and onwards, they selected significantly (P < 0.05) for A. franci scana. When offered different size classes of A. franciscana, from newly ha tched 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 weigh t 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 sel ected significantly for A. franciscana in the size class 1.20-1.39 mm. Howe ver, the larvae ingested A. franciscana shorter than 0.60 mm during the who le 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 oth er 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 compar ed to that of juvenile A. franciscana and newly hatched A. franciscana. Bas ed on the selection and digestibility results the feeding regime for halibu t 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 res t of the Live feed period. (C) 2000 Elsevier Science B.V. All rights reserv ed.