Near-natural production of fingerlings


 (c) Thünen-Institut für Fischereiökologie/Marc Willenberg

Environmental enrichment during artificial breeding of salmonids: Producing fit and robust fingerlings for regional aquaculture

Increased intensification in aquaculture production raised a strong public as well as scientific debate on animal welfare. Within the present pilot and demonstration project we intend to show how salmonid species can be produced in a seminatural way, resulting in improved welfare of these fishes.

Background and Objective

Salmonid species, like trout and char, are popular aquaculture species and have been cultivated for more than 100 years. In Germany, rainbow trout dominates salmonid aquaculture production that is being cultivation in earthen ponds, raceways, net cages and recirculating aquaculture systems. In recent years, however, the consumers’ demand has been increasing for brown trout and char, making these species attractive for the food-producing sector of aquaculture, too.  

The availability of healthy and robust fingerlings is a key element to run a successful aquaculture enterprise. In the hatchery, where salmonids are reproduced artificially, yolk-sac larvae and juveniles commonly grow up in a barren rearing environment. The use of barren tanks and troughs facilitates daily maintenance, like cleaning, of the rearing units. In barren rearing units, however, the fish are confronted with a monotonous and artificial environment quite unlike their natural habitat. Environmental enrichment, meaning a deliberate increase in environmental complexity, is an effective measure in reducing monotonicity and provide the fish with a more natural rearing environment.

Target Group

conventional and organic aquaculturists


We consulted pilot aquaculture enterprises on environmental enrichment of the housing environment and assisted them during implementation into commercial aquaculture practice. The focus was set on measures during egg incubation and the initial period of rearing inside the hatchery as well during on-growing in earthen ponds. Working with trout and char, we reared the fish in hatching trays enriched with gravel and compared this to barren rearing units. Troughs and tanks were enriched with a layer of washed sand and compared to units without enrichment. Following the hatchery, we transferred the fish to earthen ponds. Half of the fish were reared in ponds with a moderate flow inducing moderate sustained swimming while the remaining fish were reared without flow. We sampled larvae and fish in regular intervals to check for their condition, health status as well as their growth.     

Our Research Questions

Studies applying environmental enrichment on fish documented a wide range of different effects. Some of these findings clearly indicate that environmental enrichment may not only be beneficial in reducing maladaptive traits but that environmental enrichment also has the potential to improve fish welfare.

In cooperation with conventionally and organically producing local aquaculturists, we investigated how salmonid fishes (rainbow trout, brown trout, brook trout and hybrids of brook trout x Arctic charr) can be produced in a seminatural way. Within the project, we implemented recent findings on environmental enrichment into aquaculture practice. In addition, we established variable flow conditions in earthen ponds, inducing moderate sustained swimming during the rearing process of juvenile salmonids.



Involved Thünen-Partners

Funding Body

  • Federal Ministry of Food und Agriculture (BMEL)
    (national, öffentlich)


10.2014 - 7.2017

More Information

Projekt type:
Project status: finished


hits: 4

  1. Reiser S, Pohlmann DM, Blancke T, Koops U, Trautner J (2021) Environmental enrichment during early rearing provokes epigenetic changes in the brain of a salmonid fish. Comp Biochem Physiol D Genomics Proteomics 39:100838, DOI:10.1016/j.cbd.2021.100838
  2. Reiser S, Sähn N, Pohlmann DM, Willenberg M, Focken U (2021) Rearing juvenile brown Salmo trutta (L.), and rainbow trout Oncorhynchus mykiss (Walbaum), in earthen ponds with and without an induced current. J Appl Aquacult 33(1):32-52, DOI:10.1080/10454438.2019.1678545
  3. Reiser S, Pohlmann DM, Koops U, Gröger JP, Focken U (2019) Using gravel for environmental enrichment in salmonid hatcheries: The effect of gravel size during egg incubation, endogenous and first feeding in rainbow trout. J Appl Ichthyol 35(2):465-472, DOI:10.1111/jai.13884
  4. Sähn N, Pohlmann DM, Willenberg M, Reiser S (2018) Naturnahe Gestaltung der Haltungsumgebung in der Aufzucht juveniler Salmoniden zur Erzeugung leistungsstarker und robuster Setzlinge für die heimische Aquakultur: Projektabschlussbericht FKZ: 2813MDT902 Berichtszeitraum: 01.10.2014-31.07.2017. Hamburg: Johann Heinrich von Thünen-Institut, 27 p
    pdf document (limited accessibility) 966 kb