Live feed determines the survival of fish larvae
Most people are probably aware that there are fish at BalticWaters Fish Laboratory. But the laboratory also houses something else, something considerably smaller. In the live feed laboratory, plankton are cultured: tiny organisms that form the base of the marine food web and are essential for fish larvae to survive and develop. The laboratory has gradually built up its own plankton production to ensure that research projects always have access to the right feed at the right time.
The start of life: the right feed at the right time
During their earliest life stage, most fish larvae rely on their yolk sac, which provides nourishment for the first few days after hatching. Once the yolk sac has been depleted, the larvae must begin hunting and feeding on their own. In the wild, fish larvae eat different types of plankton, and it goes the same for the cods in the ReCod project.
“A cod larva changes its diet several times during its early life. The larvae begin by eating very small organisms and gradually move on to larger plankton as they grow,” says Vincent Néron, project manager for ReCod.
This places high demands on precision in the laboratory, both in terms of which plankton species are cultured and when they are fed to the larvae.
A concentration of phytoplankton. Photo: Frida Tornberg
Phytoplankton and zooplankton
To meet the fish larvae’s need for live feed, different species of both zooplankton and phytoplankton are cultured in the live feed laboratory.
Zooplankton are the main source of food for the fish larvae. These include copepods, rotifers and Artemia.
“I feed the herring larvae in the CLUPEA project with zooplankton, mainly copepods and rotifers,” says Hiba Jasmin, research assistant with CLUPEA, who is currently preparing for the hatching of herring larvae this autumn.
Rotifers are microscopic animals that grow to about 1 mm in size.
Phytoplankton, such as Nannochloropsis, Tisochrysis and Tetraselmis, are used, among other things, as feed for the zooplankton cultures.
In addition to serving as feed, phytoplankton also plays an important role in the tank environment. They contribute to what is often called “green water”, an environment that can improve the larvae’s ability to find food, reduce stress and stabilise water quality. At the same time, phytoplankton form the base of the food web: they are consumed by zooplankton, which in turn become food for the fish larvae.
Revitalised plankton as live feed
In addition to culturing its own zooplankton, the laboratory also has access to a product called CryoPlankton, developed by the Norwegian company Planktonic. It consists of cryopreserved plankton larvae that are thawed and revitalised in seawater, causing them to come back to life and begin swimming again. They can then be fed directly to the fish larvae as live feed, without the otherwise time-consuming culturing process.
Tanks with cryopreserved barnacle larvae. Photo: Frida Tornberg
Cryo-frozen feed is thawed before being given to the fish larvae. Photo: Frida Tornberg
Thawed feed, ready to be given to the larvae. Photo: Frida Tornberg
The live feed laboratory has become a central part of the facility’s operations. By culturing and adapting live feed to the fish’s developmental stage, researchers can create more natural conditions and gain a better understanding of what larvae need in order to survive, grow and cope with environmental change.
This is essential both for research and for efforts to strengthen vulnerable fish stocks in the Baltic Sea.