Weaning of Atlantic cod (Gadus morhua) and Atlantic halibut (Hippoglossus hippoglossus). Studying effects of dietary hydrolysed protein and intestinal maturation as a marker for readiness for weaning

• Published in: Aquaculture Research
• Main Author: Kvåle, Audil
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2006
• Subjects: VDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Marinbiologi: 497; atlantic cod; Gadus morhua
• Online Access: https://hdl.handle.net/1956/2128

The gastrointestinal tract of marine fish larvae undergoes extensive changes during the larval stage. The success in weaning increases as the juvenile stage approaches and the gastrointestinal tract attains a more adult-like form and functionality. In the present study, intestinal maturation in Atlantic cod (Gadus morhua) and Atlantic halibut (Hippoglossus hippolgossus) larvae was compared with weaning studies to give an indication whether intestinal maturation and weaning success were correlated. Activities of the brush border membrane (bbm) enzymes alkaline phosphatase (AP) and leucine aminopeptidase N (LAP) were used as markers for for intestinal maturation. In addition, the activity of intestinal leucylalanine peptidase (Leu-ala) was used as a marker for larval mode of digestion, but this marker gave no information in decline in larval digestive features in cod and halibut. The specific activities of AP and LAP increased abruptly from 30 to 40-50 dpff in both species, corresponding to 50-120 mg wet weight in halibut and 7-9 mm standard length (SL) in cod. These increases mark the time when the intestine achieves a more adult-like functionality, and thus, the fish larvae were considered to be better prepared to digest microparticulate diets. Comparison of intestinal maturation with early weaning studies with cod and halibut indicated that intestinal maturation was important for succeeding in weaning of these two species. However, several factors are supposed to influence the weaning results, and in particular the suitability of the diet. Marine fish larvae absorb hydrolysed protein more efficiently than intact protein. Thus, including part of the dietary protein in a hydrolysed form is thought to enhance growth and development during the larval stage when the gastrointestinal tract is not fully mature. Graded levels of pepsin hydrolysed protein (from 0 to 40-45 %) were included in the weaning diets for cod (11 mg wet weight) and halibut (120 and 220 mg wet weight) in order to define the optimal level of ...