How much proteins, carbohydrates and fat should halibut juveniles be fed?

Feed for halibut juveniles should contain more than 58 % protein, 5-25 % fat and less than 5 % carbohydrates. These are the results of a research collaboration between NIFES and the Institute of Marine Research. The nutritional requirements in young halibuts are different from those of cod juveniles and larger halibut, which have a lower need for proteins and tolerate more carbohydrates.

Low utilization of starch
The research project examined how protein, fat and carbohydrates in feed for small halibut juveniles (0,5-7g) can vary without reducing growth and survival. We varied the composition of nutrients between 0-15 % starch, 5-30 % fat and 53-83 % protein. Results showed that halibut juveniles should not have more than 5 % starch in their feed. An increase to 15 % starch gave almost a four time increase in liver index (weight of liver compared to weight of total fish) and 20 times higher glycogen content in the liver. This shows that halibut larvae have low utilization of carbohydrates for energy, which instead are being stored as glycogen in liver. A high level of starch in the diet also resulted in reduced growth.

The same experiment also showed that variation of dietary fat-content between 5 and 25 % did not affect growth, as long as the level of starch was 0-5 %. 30 % fat gave high growth with no starch added, but reduced growth with 5 % dietary starch added. This last group was fed 53 % protein, which is probably lower than the protein requirement for juvenile halibut (see below).

Variation in fat and protein
In a follow-up-experiment, the content of fat and protein in the feed varied from 5-30 % and 62-68% respectively, in a starch-free diet. The results confirm the conclusion from the first experiment, that fat and protein levels can vary widely without affecting growth of halibut larvae. The mortality in this experiment increased with increasing dietary lipid level, a trait that has not been found before. We think that this is due to increasing levels of soy-lecithin (phospholipid), which was given as a fixed fraction of total fat. Increased levels of fat in the feed also gave higher fat-content in the fish. Our results show that 62 % protein is sufficient in feed for halibut juveniles. This is in agreement with the literature which indicate a protein requirement of 58 % in young halibut.

Contact:
Kristin Hamre, phone: 55 90 51 30


References
Hamre, K., Øfsti, A., Nœss, T., Nortvedt, R. & Holm, J.C. (2003) Macronutrient composition in formulated diets for Atlantic halibut (Hippoglossus hippoglossus, L.) juveniles ? A multivariate approach. Aquaculture 227, 233-244.
Hamre, K., Bœverfjord, G. and Harboe, T. (2005) Macronutrient composition of formulated diets for Atlantic halibut (Hippoglossus hippoglossus, L.) juveniles II: Protein:lipid levels at low carbohydrate. Aquaculture 244, 283-291.