Intensive aquaculture practices can be stressful for fish. Confined spaces and repetitive routines do not replicate their natural environment, which can lead to behavioral problems, reduced immunity, and even mortality.
In this scenario, one of the aquaculture industry’s main challenges is to improve organisms’ welfare in farming systems. A new research suggests a surprisingly simple solution: adding ropes to fish farming tanks!
A study conducted by scientists from FishEthoGroup Association (Portugal), the Center of Marine Sciences of the University of Algarve (Portugal), the Portuguese Institute of the Ocean and the Atmosphere, the Association for a Sustainable and Smart Aquaculture (Portugal), and the Mediterranean Institute for Advanced Studies, Mallorca (Spain), experimentally evaluated the behavioral and physiological effects of ropes suspended inside breeding tanks on gilthead sea bream (Sparus aurata) breeders, assessing the potential use of such structures in production units.
Environmental enrichment: a promising solution
In nature, fish swim in complex environments filled with hiding spots, currents, and various objects to explore. Unfortunately, standard aquaculture tanks often lack these elements, which can lead to stress and abnormal behaviors in captive fish.
Environmental enrichment, also known as structural enrichment, involves adding complexity to farming systems, especially tanks, with structures, objects, or other modifications. According to the Environmental Enrichment Guide published by the Fish Ethology and Welfare Group, “environmental enrichment is providing sensory and motor stimulation to help meet the behavioral, physiological, morphological, and psychological needs while reducing stress and the frequency of abnormal behaviors.”
Studies on salmon, trout, and other fish have shown that environmental enrichment can:
- Reduce stress: Environmental enrichment can lower stress hormone levels, indicating a calmer and more positive state for the fish.
- Improve behavior: Fish in enriched environments tend to show less aggression and engage in more natural behaviors such as exploration and foraging.
- Enhance cognitive function: Some studies suggest that environmental enrichment can even improve memory and learning capabilities in fish.
While environmental enrichment has been successful with other fish species, its effects on gilthead sea bream, particularly on breeders, have not been thoroughly studied. The research examines the impact of environmental enrichment on adult gilthead sea bream using ropes suspended inside the tanks. These ropes mimic elements of seagrass beds, a natural habitat for this species.
Fish with enrichment options show positive behavioral changes
The researchers compared the behavior of gilthead sea bream in tanks with and without ropes over six months. They regularly recorded videos of the fish before, during, and after feeding, and throughout the experiment, they took biometrics and blood samples for plasma biochemical analysis (cortisol, glucose, and lactate).
According to the study results, gilthead sea bream in enriched tanks displayed a wider range of behaviors, including:
- More natural swimming patterns: The ropes encouraged movement away from the tank walls, mimicking their natural environment.
- Increased social interaction: The ropes provided a new element in the tank, potentially sparking curiosity and interaction among the fish.
- Improved foraging behavior: The ropes seemed to stimulate the fish’s natural hunting instincts.
- Reduced stress: While cortisol levels initially decreased with enrichment, the effect faded over time.
Easy to implement, significant impact on welfare
The good news? This enrichment technique is affordable and easy to integrate into existing aquaculture systems. Land-based tanks, commonly used in modern fish farming, can easily incorporate suspended ropes without major modifications.
Overall, this study highlights the potential of structural enrichment to improve the welfare of farmed fish. By providing a more stimulating environment, we can ensure that these important food sources thrive while minimizing stress.
Conclusion
According to scientists, simple structures like suspended ropes modified the spatial distribution of gilthead sea bream, increasing the use of interior areas and lower layers of the tank, and improving space use and exploratory behavior.
While the study is promising, more research is needed to fully understand the long-term effects of enrichment and optimize its use in different fish species and farming systems. Other studies have shown that enriched farming systems reduce the risk of diseases.
This is an important step forward in improving fish welfare in aquaculture and paves the way for more sustainable and ethical fish farming practices.
Reference
Oliveira, A. R., Cabrera-Álvarez, M. J., Soares, F., Diáz-Gil, C., Candeias-Mendes, A., Saraiva, J. L., & Arechavala-Lopez, P. (2024). Structural enrichment promotes natural behaviour and welfare of captive gilthead seabream broodstock. Applied Animal Behaviour Science, 275, 106289. https://doi.org/10.1016/j.applanim.2024.106289
