Abstract
In the last decade, the intensification of aquaculture practices, increasing number of facilities, number of species produced and rearing densities, have led to environmental stress, reduction of water quality, increase of chronic stress, growth impairment and health problems, all indicators of the reduction of the welfare of farmed fish (Saraiva et al., 2019). Recently, one of the tools that has been recommended to guarantee or improve the welfare of captive fish is the application of environmental enrichment (EE) (Brydges & Braithwaite, 2021). Structural, sensory, social, nutritional, or occupational EE aim to provide an adequate breeding environment, reduce stress to a minimum and meet the behavioural needs of individuals, promoting good welfare (Näslund & Johnsson, 2016).
For instance, structural enrichment improved survival rates and the physiological stress response, reduced stereotypical behaviour and aggressiveness, and enhanced cognition, exploratory behaviour, and brain physiological functions, among other positive effects on fish welfare (Neto & Giaquinto, 2020; Arechavala-Lopez et al., 2019, 2020; Räihä et al., 2019). However, most of these studies are focused on early-life fish stages or on-growing phases and there is still a lack of knowledge particularly on the broodstock. In this study, we measured behavioural and physiological indicators to assess the effects of structural environmental enrichment on the welfare of gilthead seabream broodstock.
Over the course of 5 months, 60 adult seabreams, distributed in six 3,000 L cylindrical tanks, were filmed regularly before, during and after feeding, cleaning, and sampling procedures. Three of the tanks were enriched with nine hanging organic ropes on 1 m2 floating structures, while the other three tanks had no enrichment (control). Operational welfare indicators (OWIs) recently developed for farmed seabream were used and adapted to build an ethogram for the broodstock behaviour analysis.
Overall, fish in enriched tanks present a darker colour and perform more aggressive displays (erect fins, chases and flight behaviours, p<0.001). The enrichment structures also influence the swimming activity in the tank, since fish in enriched tanks behave more independently and vigorously (p<0.001 and p=0.045, respectively), and forage more actively (p=0.014), while fish in control tanks seem to school more (p<0.001). Moreover, fish on enriched tanks presented a significantly higher final weight (p=0.049) than fish from control tanks. The feeding event also had an effect on behaviour, especially on the spatial distribution of the fish in the tanks (p=0.045 for horizontal distribution; p=0.013 and p=0.011 for vertical distribution, respectively). Physiological analysis of cortisol are in process, which will allow us to check the effects of structural enrichment on stress hormones of seabream broodstocks.
It should be highlighted that this is the first study carried out on seabream broodstock, where we demonstrate that simple structural enrichment can induce positive changes on fish behaviour and welfare without major changes in rearing protocols, and therefore, they might be implemented at larger scale.
References
Saraiva, J.L., Arechavala-Lopez, P., Castanheira, M.F., et al. (2019) A Global Assessment of Welfare in Farmed Fishes: The FishEthoBase. Fishes 4(2): 30. https://doi.org/10.3390/fishes4020030
Brydges, N.M., Braithwaite, V.A. (2009) Does environmental enrichment affect the behaviour of fish commonly used in laboratory work? Applied Animal Behaviour Science 118: 137-143. https://doi.org/10.1016/j.applanim.2009.02.017
Näslund, J.; Johnsson, J.I. (2016) Environmental enrichment for fish in captive environments: effects of physical structures and substrates. Fish and Fisheries, 17(1): 1-30. https://doi.org/10.1111/faf.12088
Neto, J.F., Giaquinto, P.C. (2020) Environmental enrichment techniques and tryptophan supplementation used to improve the quality of life and animal welfare of Nile tilapia. Aq Rep. 17, 100354. https://doi.org/10.3390/ani11102979
Arechavala-Lopez, P., Diaz-Gil, C., Saraiva, J.L., et al. (2019) Effects of structural environmental enrichment on welfare of juvenile seabream (Sparus aurata). Aquacult. Rep. 15, 100224. https://doi.org/10.1016/j.aqrep.2019.100224
Arechavala-Lopez, P., Caballero-Froilán, J.C., Jiménez-García, M., et al. (2020) Enriched environments enhance cognition, exploratory behaviour and brain physiological functions of Sparus aurata. Sci Rep. 10, 11252. https://doi.org/10.1038/s41598-020-68306-6
Räihä, V., Sundberg, L.R., Ashrafi, R., et al. (2019) Rearing background and exposure environment together explain higher survival of aquaculture fish during a bacterial outbreak. J Appl Ecol. 56: 1741-1750. https://doi.org/10.1111/1365-2664.13393