A sensitive period during first feeding for the determination of pigmentation pattern in Atlantic halibut, Hippoglossus hippoglossus L., juveniles: the role of diet

Six groups of Atlantic halibut, Hippoglossus hippoglossus L., larvae were o ffered calanoid cope pods at different periods from days 11 to 25 after fir st feeding (1.13-3.20 mm myotome height) in order to establish at which sta ge normal pigmentation was determined. Artemia nauplii enriched with an oil emulsion were used prior to and after the copepod period. Control groups w ere fed on copepods or Artemia only. The Artemia diet initiated an earlier intake of food and higher initial growth compared to the copepod diet. Afte r 50 days of feeding, the average dry weights of the fish fed on Artemia an d copepods were quite similar to the copepod-fed fish, while the Artemia-fe d fish were the smallest in size. The lowest frequency of normally pigmente d juveniles was found in the Artemia-fed group (66.4%), while the copepod g roup showed almost 100% normal pigmentation. A significantly higher frequen cy of pigmentation was found in juveniles given a copepod diet close to the initiation of metamorphosis than those provided with an earlier copepod pe riod of equal duration. A high degree of eye migration was found in all gro ups, but was lowest in the Artemia-fed group. The initial stage of eye migr ation was found to occur at a larger body size in fish given Artemia and co pepods, or a copepod diet than in fish fed on Artemia alone. There was no s ignificant correlation between eye migration and growth rates prior to meta morphosis, although the largest individuals exhibited the most complete eye migration. High pigmentation frequencies were obtained in fish with a low 22:6n-3:20:5n-3 (DHA:EPA) ratio (< 1.0).