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 offered calanoid cope pods at different periods from days 11 to 25 after first feeding (1.13-3.20 mm myotome height) in order to establish at which stage normal pigmentation was determined. Artemia nauplii enriched with an oil emulsion were used prior to and after the copepod period. Control groups were fed on copepods or Artemia only. The Artemia diet initiated an earlier intake of food and higher initial growth compared to the copepod diet. After 50 days of feeding, the average dry weights of the fish fed on Artemia and copepods were quite similar to the copepod-fed fish, while the Artemia-fed fish were the smallest in size. The lowest frequency of normally pigmented juveniles was found in the Artemia-fed group (66.4%), while the copepod group showed almost 100% normal pigmentation. A significantly higher frequency of pigmentation was found in juveniles given a copepod diet close to the initiation of metamorphosis than those provided with an earlier copepod period of equal duration. A high degree of eye migration was found in all groups, but was lowest in the Artemia-fed group. The initial stage of eye migration was found to occur at a larger body size in fish given Artemia and copepods, or a copepod diet than in fish fed on Artemia alone. There was no significant correlation between eye migration and growth rates prior to metamorphosis, 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).