Freshwater fishes are some of the most imperilled animal species (IUCN, 2021). They are under threat of extinction due to climatic change, anthropogenic impacts on their habitats and populations, and pressure from invasive species and human exploitation. Approximately 51 percent of all fish live in freshwater, numbering an estimated 18,000 species (WWF, 2021).
Conserving freshwater fish species requires consideration of their behaviour patterns and ecology to uphold good fish welfare when housed ex situ (“under human care”), and ex situ populations require a comprehensive and adaptive approach based on the species, its needs and its specific requirements.
Why is conservation of ex situ freshwater fishes important?
Many species of the freshwater fishes that are common in the home aquarium and come from captively reared populations are actually threatened in the wild (Raghavan et al., 2013). Careful stewardship of such populations is required to ensure their long-term survival.
For example, the popular and striking red-tailed black shark (Epalzeorhynchos bicolor) has been listed at critically endangered on the IUCN Red List since 2011 (Vidthayanon, 2011) and only one population is thought to remain in the wild. However, developments in management and husbandry mean that the population used for the ornamental aquarium trade is sustainably captive bred. In the case of these red-tailed black sharks, understanding the physiology of their endocrine system has enabled spawning to be induced via hormonal stimulation (Shireman and Gildea, 1989). This, in turn, has been influential in the development and maintenance of captive populations for the aquarium trade.
What do we need to know about freshwater fish for conservation?
Reducing pressures on free-living populations (eg by developing captive breeding systems) is essential for long-term freshwater fish conservation.
Reducing pressures on free-living populations is essential for long-term freshwater fish conservation
Freshwater fishes are important biological indicators for the health of wetland habitats. Their presence indicates the quality of water chemistry and resources (available for many different species) in the wetland. Information from wild and ex situ populations can help with species-focused conservation efforts (Figure 1).
Freshwater fishes can be keystone species in the habitats where they occur, so their continued presence within an ecosystem is essential. Atlantic salmon (Salmo salar) or Arctic grayling (Thymallus articus), for example, support other populations of different species in the same habitat – without the presence of these fish, the ecosystem would struggle or collapse (Golden et al., 2021; Woodward et al., 2021). Therefore, maintaining the health of keystone fish populations has a beneficial knock-on effect for many other living creatures too and upholds the resilience and functionality of the wetland.
The worldwide ornamental aquarium fish trade is worth billions of dollars to the global economy (Evers et al., 2019). However, there are also enormous animal welfare costs associated with the harvesting, transportation, selling and housing of such fish species (Kristiansen et al., 2020). Reducing welfare compromises and unsustainable pressures on wild populations as a result of the demands of the aquarium fish trade is an industry priority.
Knowledge of animal behaviour and species-specific behavioural ecology (how behaviour provides an adaptive benefit in an environment) is vital for continual development of (Stevens et al., 2022):
- Conservation action
- Relevant husbandry and management practices
- How we assess and promote good fish welfare
By understanding how fish behave, how they interact socially and with their environment and how they grow, mature and age, captive housing and husbandry can be as species-relevant (and as welfare-friendly) as possible. Studies of fish cognition, perception and problem-solving abilities can also shed light on psychological aspects of well-being (Brown, 2015; Pouca and Brown, 2017) and these positive welfare outputs need to be catered for in captive settings (Sánchez-Suárez et al., 2020).
By understanding how fish behave, how they interact socially and with their environment and how they grow, mature and age, captive housing and husbandry can be as species-relevant (and as welfare-friendly) as possible
How do we conserve freshwater fish populations?
Using our understanding of species biology and ecology, we can consider the following examples of practical freshwater fish conservation and management that would help support population sustainability and health and welfare.
- Habitat restoration and protection:
- Identify critical habitat areas and resources, such as spawning grounds, nursery sites and areas used for shelter and respite, and implement measures to protect them from degradation or human disturbance
- Research how specific habitat areas are used at different fish life stages and ensure they are available
- Restore degraded habitats by removing barriers to fish movement, controlling invasive species and replanting native vegetation that can improve the quality of the habitat
- Population connectivity and fish movements:
- Constructing fish passages (eg salmon ladders) around dams, weirs and other barriers to migration enables fish to access spawning areas unhindered
- Restore rivers to pre-culverted or similar “tamed” states to improve water flow, water chemistry and attractiveness of the river for fish populations
- Water-quality enhancements:
- Manage to eliminate any sources of pollution that escape into water courses to maintain suitable water quality for fish survival and reproduction
- Reduce nutrient loading to prevent harmful algal blooms and eutrophication that leads to oxygen depletion, the occurrence of anaerobic conditions and fish die-offs
- Targeted in situ conservation action:
- Establish protected areas that safeguard critical freshwater habitats for species’ needs
- Enforce regulation to prevent destructive activities within protected areas
- Implement control and eradication programmes of invasive species that disrupt native ecosystems and important fish behaviours that hinder population recovery
- Work with local communities to ensure fish populations are valued and considered important for protection
- Involve indigenous communities, which possess traditional knowledge of fish behaviour and ecology when planning for species and habitat conservation work
Ex situ populations
Similarly, conservation action can also involve aquaria and ex situ facilities. Ensuring that captive fish are correctly managed means individuals will behave normally, be in good condition to attempt breeding and have a normal longevity (Figure 2).
Such aspects of good management can include:
- Appropriate landscaping and design of aquariums:
- Create managed environments that mimic the natural habitat of a species, providing spaces for different behavioural outputs
- Use appropriate substrates, plants and decorations to stimulate natural behaviours for all species housed in an aquarium (to reduce competition, aggression, bullying or harassment)
- Social compatibility:
- “Community tanks” are very popular but fish species in them need to be carefully selected
- Choose fish species that are compatible behaviourally or that will not directly compete over resources and ensure social hierarchies are maintained to minimise stress and aggression
- Avoid overcrowding as this leads to territorial disputes and aggressive encounters that can escalate when individuals cannot remove themselves from the immediate area
- Use environmental enrichment:
- Design and implement environmental enrichment programmes based on species biology to promote behaviours of importance
- Provide opportunities for positive behavioural diversity by, for example, enhancing foraging opportunities or exploration or social interactions within a shoal
- Reduce the impact of external stressors (eg any negative impact of human observers) by providing planting, furnishings or habitat features that make species feel comfortable and secure within their aquarium
Through the integration of these different management approaches and by tailoring them to the specific needs of each freshwater fish species and their ecosystem, conservation efforts can effectively uphold fish welfare (eg by ensuring fish can develop, grow and live out their lives naturally) and contribute to the long-term survival of wetland environments (eg by conserving and ensuring the continued functionality of any ecosystem services provided by the wetland).
Conserving the important behaviour patterns of freshwater fishes in the wild and aquaria requires a combination of scientific knowledge, ethical considerations and practical measures
Conserving the important behaviour patterns of freshwater fishes in the wild and aquaria requires a combination of scientific knowledge, ethical considerations and practical measures. A holistic approach to freshwater fish management, involving health, welfare, species and habitat conservation, and population stewardship will ultimately work most effectively in securing a bright future for many species that are utilised by humans.