Near-natural production of fingerlings

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

Approach

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.