Interreg Projekt Alge4Fish

The mass rearing of healthy fish larvae is an important production step in aquaculture. Fish larvae of some species, especially of the Salmonidae family, can be fed with dry feed mixtures right from the start. However, the rearing of more sensitive freshwater and marine fish larvae is heavily dependent on live feed. Since dry feed offers economic advantages, intensive research efforts have been made to replace live feed with dry feed. However, no reliable recipes are currently available. This is mainly attributed to an unbalanced nutrient composition and low digestibility of the feed particles due to the underdeveloped digestive tract of fish larvae. In addition, the deterioration of water quality in the rearing tanks is another disadvantage of the types of dry feed currently available.

For economically relevant freshwater fish such as zander, perch, eelpout, European catfish and certain coregonid species, larval rearing only works with live food. The aim of the project presented was the cultivation and production of microalgae (phytoplankton) on useful and residual water. This phytoplankton is used as a food source for live food cultures (rotifers, protozoa), which in turn are used as feed for various fish species. These live food cultures were tested for their suitability as fish food for fish larvae. To date, there is no direct comparison of the effectiveness of the different types of live food. It is also still unclear whether there is a species-specific preference for different types of live food. This data is of great importance for rearing fish farms in order to select the most suitable feed types and feeding systems. This project has combined expertise in water utilization, microalgae cultivation and fish farming and utilized expert knowledge across disciplines.

The project produced the following results: Rotifers (Brachionus plicatilis, Brachionus calyciflorus) and the protozoan Paramecium bursaria were successfully reared with phytoplankton cultivated on residual water. Feeding trials were carried out on zander, eelpout and whitefish. Copepods, which were fished from sea plankton, were used as comparative feed (control). Survival rate, weight gain and malformation rate of the fish larvae were examined as a measure of rearing success.

Freshwater rotifers or Paramecium bursaria are best suited for the first feeding of zander larvae for a period of up to 10 days. Following this food, copepod and Artemia nauplii were tested. Copepod nauplii were superior to Artemia nauplii, as higher survival rates and more homogeneous growth were achieved with the former. In order to ensure the transferability of these findings, additional studies were carried out on eelpout and whitefish. Like zander larvae, eelpout larvae could initially be fed with freshwater rotifers or Paramecium bursaria. However, copepod nauplii were just as suitable. As for the zander, copepod nauplii were also a better follow-up food for the eelpout than Artemia nauplii.

For the whitefish, initial feeding with freshwater rotifers or Paramecium bursaria did not bring any advantages. Feeding copepods from the beginning was optimal. Artemia was also suitable for the larvae of this fish species.