Fish nutrition and husbandry

The steady growth of the aquaculture sector also creates a steadily increasing demand for feed and feed raw materials. This leads to new challenges in the feed sector, both from an ecological and an economic point of view.

The increasing demand, but also international crises, lead to rising raw material prices, which are reflected along the entire value chain.

At the same time, the use of globally available resources in fish feed influences its ecological footprint due to long delivery and transport routes.

The working group on fish nutrition and husbandry has set itself the goal of identifying locally available by-products of food and feed production and evaluating them for their suitability as raw materials for fish nutrition.

The scientists of the Fraunhofer IMTE cooperate with many companies from the feed and feed raw materials sector in the development of feeds with special requirements such as the nutrition of marine fish larvae or the nutrition of fish in closed recirculation systems (RAS).

One of the biggest challenges of aquaculture is to find sustainable alternatives to fishmeal and fish oil in the diets of many aquaculture-relevant species.

Many of the species already used commercially in aquaculture feed naturally on fish, which makes this raw material the ideal basis for a diet that meets their needs, but at the same time has a strong negative impact on the sustainability and environmental justice of fish feed.

In the search for alternative raw materials, both renewable, plant-based alternatives, single-cell alternatives such as yeasts or fungi, and alternatives of animal origin from side streams of the food and cosmetics industry are being investigated in more detail.

In addition to the identification of new raw materials, special attention is paid to the aspects of sustainability, compatibility and usability (digestibility and retention) of the raw materials, as well as to the growth performance of the organisms in order to evaluate and, if necessary, optimise them if corresponding problems are identified during establishment.

Replacing fishmeal with alternative plant-based raw materials poses many new challenges, such as antinutritive factors in the form of plants' storage substances for minerals, plants' antifeedants against pests and other plant-based components to which, from an evolutionary point of view, aquatic organisms would not be exposed naturally.

For example, certain storage forms of minerals cannot be broken down by the fish's digestive system, as the required enzymes are not provided for in the fish's digestive "construction kit". As a result, certain minerals have to be added to the feed, even though they are sufficiently available in the plant source, in order to meet the requirements of the respective species.

In order to make fish feed as resource and environmentally friendly as possible, such "overdosing" must be avoided.

Therefore, one research focus of the working group is on the use of enzyme additives to increase the usability and digestibility of plant raw materials as well as the use of functional feed components to improve the compatibility and utilisation of plant raw materials. 

Compared to classical agriculture, the potential of usable animal species is far from exhausted. The diversity of animal organisms used in aquaculture exceeds that of classical agriculture by far.

There is much less validated knowledge about the animal species already used in aquaculture than for the "big four" of agriculture (pigs, cattle, poultry, sheep).

For many economically interesting aquaculture species, such as eel or tuna, it has not even been possible to completely close the life cycle in production.

This is often due to a lack of knowledge on the exact micro- and macronutrient requirements of the different life stages of the respective species.

In order to close these knowledge gaps and thus enable a more sustainable production of these species that is more appropriate to their needs and animals, the WG Fish Nutrition and Husbandry is dedicated to research in this area. Among other things, research focuses on the need for certain minerals, essential amino acids and essential fatty acids of various aquaculture-relevant species. 

Closed-loop systems offer the possibility of producing non-native species locally in a more sustainable and environmentally friendly way than in the countries of origin due to their decoupling from various environmental influences, such as photoperiod, climate and water supply. Shrimps (L. vannamei) are a good example: During production in the countries of origin, the environment is often heavily polluted (mangrove deforestation) and the end product has long transport routes.

However, in order to be able to produce these species in closed systems, precise research into the optimal husbandry conditions is necessary.

The working group is addressing this issue by using various techniques, such as group respirometry to determine the metabolic states of the animals or the use of small-scale systems in which, in a replicate approach, one or more environmental parameters can be manipulated simultaneously in a targeted manner.