A balanced diet yields best-formed cod
Slight changes in feed composition for cod larvae could result in fewer deformed cod in Norwegian sea cages. But there is no single diet that ensures healthy-looking cod.
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.
“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.
“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.”
|Wild cod as environmental indicators|
Extensive research has generated knowledge that could give wild cod an important role in monitoring the environment.
“Cod has been the subject of much research in recent years – but that is no reason to reduce the level of activity. In fact, just the opposite,” asserts Mari Moren.
Dr Moren says that cod is now one of the best-described species in the world. She has personally contributed to this through her TOPPFORSK project, which is building up detailed knowledge about bone-regulating genes in cod.
“In the course of the project we have developed tools for studying very young cod. These provide good models for research in other areas besides aquaculture. The models are well suited to understanding cod larvae in the wild and using them as indicators of the effects of, for example, temperature change, oil spills, CO2 levels, and changes in the marine food chain,” explains Dr Moren. “I believe that continued research activity on cod will pay off in terms of knowledge about the impacts of climate change.”
“We now know what the optimal levels of the various nutrients are, and this can help us to understand how changes may affect wild cod stocks in the future. Global warming, for instance, may alter the composition of nutrients in the food of wild cod, which will affect their expected growth and survival capabilities,” she concludes.
- Last updated: