领域：学术论文 · 自然科学

Abstract
Food-based environmental enrichment (EE) is a valuable strategy for stimulating foraging behaviour in fish under human care, as it increases the challenge of food acquisition and encourages prolonged engagement in this activity. Curimbas (Prochilodus argenteus) and pacus (Myleus micans) are fish species for which ex situ maintenance has become an important conservation measure. In this context, providing EE is essential to ensure high welfare standards. This study aimed to assess the effects of food enrichment on the behaviour of these two endemic species from the São Francisco River basin in Brazil. Behavioural data were collected across three experimental phases, including baseline, enrichment, and post-enrichment. Slow-dissolving food items known as “acorns” were introduced during the enrichment phase. Both species exhibited a marked reduction in inactivity throughout the study. For curimbas, the enrichment phase was associated with increased foraging, elevated agonistic interactions, and greater use of specific tank areas. Among pacus, inactivity significantly declined during the enrichment period. Additionally, the presence of visitors influenced behavioural patterns, promoting foraging activity while reducing inactivity and interactions with the enrichment device. These findings reinforce the value of incorporating environmental enrichment to promote the welfare of freshwater fish in public aquariums.
1. Introduction
Environmental enrichment (EE) is a tool used to improve the welfare of animals under human care [1]. Animal welfare is generally determined by the quality of the animal’s experiences concerning five domains, namely nutrition, health, the environment, behavioural interactions, and mental state [2,3]. In other words, more positive experiences increase the animal’s well-being, and more negative experiences decrease it. Animals that live in stimulating environments and have positive experiences generally display a greater diversity of behaviours, which can be measured and used as an indicator of well-being [4]. In the case of fish, the application of EE consists of offering items to stimulate individuals, allowing them to express their motor skills, exploratory behaviours, feeding, and other behaviours that are close to natural, which tends to reduce abnormal and unwanted behaviours [5,6,7].
Foraging is a behaviour that is naturally highly exhibited in the wild, as obtaining food in this environment is often a challenge [8,9]. In zoos and aquariums, there is often a routine in the animals’ diets, with food being offered at exact times in pieces or on trays, and this does not provide a challenge to get the food, making the feeding time very quick [10,11]. Therefore, food enrichment is a documented way of stimulating foraging behaviour, making it more difficult for the animal to access the food, so it must dedicate itself to this activity for longer [12,13]. In turn, the greater display of this natural behaviour improves animal welfare [11,14,15,16].
The welfare of animals kept in zoos and aquariums can also be affected by the presence of visitors [17]. Since 2012, there has been an increase in research into the zoo visitor effect; however, only 4% of existing studies have been conducted with fish [18]. Fish displaying less social behaviour and becoming more active or showing neutral or inconclusive responses in the presence of visitors are results observed in the few studies on this subject [18,19].
Fish with low welfare levels kept under human care can develop health problems and behavioural changes due to the stress caused by artificial environments [20,21], such as apathy (remaining motionless at the bottom of the tank or spending a long time on the surface of the water), uncoordinated swimming, or increased aggression [22,23]. Some studies have shown a significant lack of research into the effects of EE on fish welfare [24,25,26,27,28], but some positive effects of EE on fish welfare have already been reported, such as increased brain development [29,30,31], a reduction in stress levels, analysed based on the amount of cortisol in the blood of the fish studied [32,33,34], improved foraging ability [12,35,36], aggression [34,37], and positive effects on body growth [38,39].
Although environmental enrichment has been increasingly studied in aquaculture and laboratory environments, a notable gap remains in research concerning aquarium-housed fish in zoological institutions, particularly in Brazil. A recent review emphasised that only a small fraction of enrichment studies focus on aquatic species kept in public aquaria [40]. Similarly, other researchers have proposed structured enrichment protocols for diverse aquarium-housed species but have highlighted the lack of empirical data for teleosts [41]. In Brazil, while aquariums play a growing role in conservation and education [42], systematic evaluations of the impacts of enrichment on native freshwater fish in public aquarium contexts are virtually absent. Furthermore, there are no published studies investigating the effects of environmental enrichment on curimbas Prochilodus argenteus or pacus Myleus micans under managed care. This scarcity underscores the novelty and relevance of the present study, which seeks to address this knowledge gap by assessing enrichment effects on behaviour and welfare in these two species within a Brazilian zoological setting.
Institutions that keep animals must always ensure that the animals under their care exhibit high levels of welfare and are in good physical and mental health so that they can fulfil their role effectively [43]. Aquariums play a vital role in the conservation of fish, particularly endangered species, given the global environmental degradation scenario. Through environmental education, these institutions raise awareness among the population, sensitising and educating them about the importance of these animals to the ecological balance [44,45].
Considering the importance of EE in ensuring the well-being of fish under human care, this study aimed to examine the impacts of EE on the behaviour of two species of fish endemic to the São Francisco River basin in a public aquarium in Brazil (curimbas Prochilodus argenteus and pacus Myleus micans). The central hypothesis is that the EE will influence the behavioural displays of the fishes studied, resulting in a decrease in inactivity and abnormal behaviours and an increase in activity and foraging behaviours during the use of the EE. In addition, more visitors in front of the pond will result in less interaction with the enrichment and an increase in the display of inactivity, aggressive behaviour, and non-visibility by the fish.
2. Materials and Methods
2.1. Ethical Note
The Belo Horizonte Zoo’s Research and Ethics Committee approved the study (protocol no. FU011/2023).
2.2. Study Place, Fish Species, and Maintenance
The study was conducted at the São Francisco River Basin Aquarium in the Belo Horizonte Zoo, Minas Gerais, Brazil (19°51′37.49″ S, 44°0′18.25″ W) (Figure 1). The São Francisco River Basin Aquarium was inaugurated in March 2010 and has 22 enclosures (tanks) that, in their various sizes and shapes, hold more than 1 million litres of water and more than 50 species of fish, most of which are native to the São Francisco basin, including endemic and endangered species [46].
The aquarium houses two popular species from the São Francisco River Basin in a community tank. The curimba Prochilodus argenteus Spix & Agassiz, 1829 (Characiformes), belongs to the Prochilodontidae family and has an iliophagous feeding habit, consuming detritus, filamentous algae, and benthic fauna . Due to its habit, the curimba plays an important role in the ecosystem, promoting greater utilisation of available nutrients by purifying waterways and cycling nutrients . The pacu Myleus micans (Lütken, 1875) (Characiformes), which belongs to the Serrasalmidae family and has a laterally compressed body with a high lateral profile, minor scales, and a long dorsal fin, is also kept with this species . Its eating habits are omnivorous, but its diet is predominantly herbivorous, consuming mainly aquatic macrophytes and filamentous algae .
We studied five pacu individuals, all adults and weighing an average of 3.2 kg, kept in the aquarium since June 2011 and originating from the Três Marias reservoir (Minas Gerais State), as well as six adult curimba individuals weighing an average of 0.6 kg, kept in the aquarium since May 2014 and originating from the São Francisco and Parnaíba Valley Development Company (Codevasf, Montes Claros, Minas Gerais, Brazil). During the study, the individuals were kept in Tank 1, which contained 32.89 m3 of water (4.4 m × 4.5 m × 2 m × 5 m × 2.3 m deep). The fish were fed daily at 4 pm with 150 g of feed produced by the zoo’s nutrition team. They were always maintained in suitable conditions for the species (mean ± SD: pH, 7.35 ± 0.14; temperature, 25.12 ± 1.02 °C; dissolved oxygen, 13.2 mg/L) .
 

翻译考点：
考点1：【environmental enrichment (EE) 】应译为 【环境丰富化】
考点2：【food-based environmental enrichment 】应译为【食物型环境丰富化】
考点3：【baseline, enrichment, and post-enrichment 】应译为 【基线期、丰富化期、后丰富化期】
考点4：【agonistic interactions】 应译为 【攻击性互动/对抗性互动】
考点5：【iliophagous feeding habit 】应译为 【食淤泥的摄食习性】
考点6：【community tank 】应译为 【混养水缸/混养水池】
考点7：【Parnaíba Valley Development Company (Codevasf) 】应译为 【帕尔奈巴河谷开发公司】