“The relationship between vitamin A and fatty acids appears to be of major significance for the degree of ossification in cod larvae,” says Mari Moren. (Photo: Torkil Marsdal Hanssen) Deformities continue to present a problem for producers of Atlantic cod. Scientist Mari Moren of Norway’s National Institute of Nutrition and Seafood Research (Nifes) has been receiving project funding under the HAVBRUK programme’s “Project for top young investigators in aquaculture research” (TOPPFORSK) since 2008. She is studying how different nutrients and vitamins strengthen bone development in cod larvae.

Early-stage causes

“In nature, animals with weak skeletons are less fit to survive than their species-mates with strong skeletons,” says Dr Moren, who heads nutritional research on early life stages of fish at Nifes. “We believe that the causes of later deformities begin at an early stage; a poor start in bone development increases the risk of skeletal damage later in life.”

Collaborating with researchers at several international research institutions, Dr Moren has been studying cod larvae of less than 1 cm in length. In comprehensive feeding trials using 16 experimental tanks at the Institute of Marine Research’s Austevoll Aquaculture Station, her research team has examined the effects of different feed compositions on bone structure development in cod.

Varied diet is best

Vitamin A was previously thought to play a critical role in bone development, but the team has discovered that it is not individual dietary components that determine eventual skeletal strength.

“There is no miracle cure. But the relationship between vitamin A and fatty acids appears to be of major significance for the degree of ossification in cod larvae. In our feeding studies we have observed multiple substances simultaneously and how they interact with each other in relation to bone development. The experiments indicate that fatty acids are just as important for the degree of ossification as vitamin A,” explains Dr Moren, who sees their findings as somewhat surprising given previous beliefs.

The skeleton of a 34-day-old cod raised on unenriched rotifers (left) is poorly developed compared to a 20-day-old cod fed on zooplankton. (Photo: Mari Moren)

Designer feed

“Our research provides fish farmers and feed suppliers with new knowledge and enhanced understanding of how to strengthen bone formation in cod during the early life stages.”

Production cod larvae are currently raised on a diet consisting primarily of rotifers produced indoors. Cod in the wild, however, eat other types of naturally-occurring zooplankton. Zooplankton yield rapid growth and stronger bone structure in the tiny cod larvae, while a diet of rotifers in their original form yields far weaker ossification and poorer growth.

“But rotifers are what they eat,” explains Dr Moren, “which means we can enrich them with various nutrients and vitamins. We now know which combinations yield the best results and how to optimally utilise rotifers as feed for cod larvae.”