Fake plants have real benefits for farmed tilapia - Part 1

The introduction of artificial water plants into tilapia aquaculture can lead to significant improvements in fish welfare at minimal expense to the farmer.

The study involved the GIFT strain of Nile tilapia. Photo WorldFish

A study taking place in Brazil revealed that environmental enrichment, in the form of artificial aquatic plants and shelters, can significantly improve tilapia welfare by reducing stereotypical and aggressive behaviour.

The study was conducted in the Experimental Farm Campus of the Aquaculture Sector of the Faculty of Veterinary Medicine and Animal Science at São Paulo State University (UNESP). It involved 640 juvenile Nile tilapia (Oreochromis niloticus) males originating from a sex-reversed GIFT population.

The first treatment was composed of environmental enrichment, using PVC pipes, 10 cm in diameter and 20 cm in length, for shelter.

The second used artificial water hyacinths (frayed nylon rope simulating the natural water hyacinth root) fixed to styrofoam structures or to the aquarium itself.

The third treatment was outlined with food supplementation with the amino acid tryptophan supplemented to the diet at 2.56 percent by weight.

The fourth treatment was a control tank without enrichment or supplemented food.

An analysis of aggressive behaviour showed lower numbers of confrontations in the tanks where the food had been supplemented with tryptophan food-supplemented treatment compared to the control and environmental enriched treatments. This is because it is a serotonin precursor, a neurotransmitter involved in the control of aggressive behaviour and the susceptibility to stress.

On the other hand water hyacinth and shelter presented high levels of confrontation.

“Despite the benefits, enriched environments can generate competition between territorial fish, which means more confrontations,” the researchers noted.

However, they also noted that environments enriched with artificial water hyacinth and shelters led to less intense confrontations, which were mostly threats rather than fighting, and concentrated at the section with enrichment items. In the control situation the occurrence of these confrontations were more intense – leading to pursuits, lateral confrontation, and bites – and occurred through the entire aquarium region.

They also noted that opercular beat frequency – another sign of stress – was lowest for the tilapia whose tanks were enriched with artificial water hyacinth.

The researchers also questioned whether the tryptophan supplementation was sufficient to act as an alternative to environmental enrichment as a means to enhance animal welfare, as their trial showed that scratching behaviour increased in the tryptophan treatment relative to the environmental enrichment treatments.

Conclusion

The researchers conclude by stating that “a poor environment in fish farming has deficiencies that can be improved by including proposed enrichments, filling a fish need to express natural behavior, improving the quality of life for animals. We can highlight artificial water hyacinths as the treatment that presented the best and most consistent results. Such a means of environmental enrichment can be easily implemented in fish farms since it is low cost, easy to handle, and highly durable.”

Environmental enrichment techniques and tryptophan supplementation used to improve the quality of life and animal welfare of Nile tilapia

The adoption of high standards of animal welfare improves the quality of life for animals being reared and produces improved end products for consumers. In this study, we investigate the role of environmental enrichment and tryptophan supplementation in increasing animal welfare indices in tilapia. To do this, the environment where fish are reared is enriched using artificial aquatic plants and shelters, and their diet is supplemented with tryptophan. Animal welfare parameters are estimated and compared to verify this enrichment. The use of environmental enrichment and tryptophan supplements significantly influences the parameters of animal welfare in Nile tilapia, indicating their preference for enriched environments by reducing stereotypical and aggressive behavior. We emphasize the contribution that this study has in applying the concept of animal welfare in fish production, given that the simple and low cost enrichments used had a positive impact on the quality of life of the animals.

Introduction

Animal welfare in fish production mainly aims to: (i) ensure a better environment for the animals; (ii) minimize potential stress during production and; (iii) provide the final product with higher added value and quality. The use of animal welfare practices has been increasing in productions and studies, in addition to humane slaughtering techniques that effectively ensure an improvement in the quality of the final product delivered, consumers also show an interest in consuming meat from productions where quality of life and the sustainability of the system are taken into consideration. 

One way of ensuring animal welfare is by using environmental enrichment, a set of techniques used to modify the environment, which is suitable and satisfactory for animal behavior by introducing artifacts or improving the breeding system. Broadly speaking, environmental enrichment aims to provide an adequate breeding environment, reduces stress to a minimum and meets the behavioral needs of individuals.

As far as we are aware, the use of environmental enrichment to promote animal welfare in fish production systems has not yet been assessed. The application of enrichment techniques for these animals provides the fish with their basic breeding needs such as access to important resources in their habitat, e.g., nesting, feeding and sheltering. 

These resources may help fish to cope with stressful events, since they have more behavioral options during the production period (Pinheiro, 2009). Early studies on environmental enrichment for fish have demonstrated the positive influence of introducing wood twigs, stones and other natural substrates or artificial plants, among others, on the morphology and foraging efficiency of captive-bred individuals.

Another way to ensure animal welfare is through dietary supplementation. For aquaculture, several authors have already investigated the effectiveness of this technique. According to Wolkers et al. (2014), diets supplemented with tryptophan show an improvement in the social relationships of animals raised in groups, and this extends to fish, given the therapeutic characteristics of this amino acid, which modulates serotonergic activity. Moreover, tryptophan supplementation provides benefits in fish production such as reducing stress (cortisol) and reducing aggressive behavior within the group (Höglund et al., 2005; Winberg et al., 2001 and Wolkers et al., 2011).

Practices such as environmental management and food supplementation that ensure a better quality of life for the animals being reared are directly related to the sustainability of production and the perceptions of sustainable fish farming. In aquaculture, Nile tilapia (Oreochromis niloticus) is one of the most important fish for human consumption, where 4.5 million tonnes of fish is produced worldwide. 

In Brazil, this fish is the main species reared for commercial purposes, with an increase of 7.96 % in 2019 when compared to 2018. According to reports by FAO (2018), Brazil is in the fourth largest producer of tilapia worldwide, with more than 432,149 tons per year. This growth in production can be explained by several factors: genetic improvement, improvement of techniques, the Brazilian potential for aquaculture production, the increase in fish consumption and net-cage fish farming. With the growth of fish production and consumer awareness of techniques used in production, animal welfare requirements that ensure fish wellbeing is highlighted as an important contribution to the aquaculture sector, aiming to create production patterns that expose fish to minimal stress and ecosystem imbalance. 

Practices that ensure animal welfare have already been used in other areas of production, such as the beef, pork, and poultry sectors, for example. However, regarding fish production, the use of such techniques is still poor. As such, the aim of this study was to evaluate the role of environmental enrichment and dietary supplementation in Nile tilapia wellbeing.

Methods

Experimental system

The study was conducted in the Experimental Farm Campus of the Aquaculture Sector of the Faculty of Veterinary Medicine and Animal Science at São Paulo State University (UNESP), Botucatu. We used 16 glass aquaria (300 liters) connected to a recirculation system with a total capacity of 12,000 liters, containing 6 biological filters and 3 ultra-violet filters. The filtered water was heated and maintained at 26 ± 2 °C using three heaters of 2,000 W before it was pumped into reservoirs located at 3 m height and distributed by gravity to the aquariums. Each aquarium contained an aeration system and a 300-watt heater to keep a constant temperature. The light period was maintained from 6 a.m. to 6 p.m. with individual illumination for each aquarium using timer-controlled 6-watt LED lamps.

The water temperature was daily measured at 8 a.m. and 5 p.m. Weekly, water samples were collected from the recirculation system and tested using the labconTest® kit to determine pH, total ammonia, nitrite and dissolved oxygen. These water quality values were maintained constant at levels of 7.0 ± 0.2, 0.37 ± 0.15 ppm, 0.16 ± 0.12 ppm and 8.0 ± 1.6 ppm, respectively, meeting the acceptable levels for fish farming throughout the experimental period.

Animals

We used a total of 640 juvenile males of Nile tilapia (Oreochromis niloticus) originating from a sex-reversed GIFT population. The initial average weight and total length of the experimental fish were 29.53 ± 2.0 g and 11.5 ± 0.37 cm.