Mikrofoto.de-Brachionus_quadridentatus (rotifer) used to feed to baby cod.
Finding the right food for larval cod has proved tricky, but scientists have recently found a way to make it more nutritious.
Growing big and strong is all about getting the right nutrients. In nature, cod larvae eat tiny copepods, packed full of zinc, selenium, manganese and copper, all of which are important minerals for the larvae. However, it is not easy to obtain copepods for aquaculture, so farmed cod larvae are often fed rotifers, a different group of microscopic aquatic organisms that are easy to culture in large amounts.
“A lack of important nutrients can lead to poor growth, deformities and other welfare problems,” says NIFES scientist Kristin Hamre. Together with colleagues from NIFES, the Institute of Marine Research, Nofima and the University of Bergen, Hamre has developed a method of adding nutrients to rotifers that give them a higher mineral content.
When they added various concentrations of zinc, selenium, manganese and copper to the food of the animals fed to cod larvae, the research team found that their nutrient content increased in line with the quantity of additives given.
“This gives us a method of controlling and adapting the nutrient content of rotifers, to bring them up to the level of copepods,” says Hamre.
However, feeding cod larvae is a complex task. The biggest challenge is to get them to grow properly through the first post-hatch period. They have a sensitive digestive system and must not be given too little in the way of minerals, while too much can have toxic effects.
In order to find out just how much they can tolerate, the scientists performed an experiment in which cod larvae were fed rotifers with different concentrations of iodine or selenium. The results showed that the group that was given only small extra amounts of minerals managed best. The groups that were fed no mineral supplements and those given as much as occur in copepods, were less likely to grow properly.
“Now we need to do more research on the cod larva’s total nutrient requirements. But we have already made an important step forward in our efforts to find the optimal feed for cultivated cod larvae,” says Kristin Hamre.