Turkish freshwaters as a case of rising invasion risk of aquarium fishes under climate change – Nature

Report on the Rising Invasion Risk of Aquarium Fishes in Türkiye under Climate Change

Abstract

This report assesses the escalating invasion risk of non-native aquarium fish in Türkiye, a critical issue impacting the achievement of Sustainable Development Goal 14 (Life Below Water) and SDG 15 (Life on Land). Climate change, a central concern of SDG 13 (Climate Action), is identified as a significant amplifier of this threat. A screening of 46 popular ornamental freshwater fish was conducted using a Basic Risk Assessment (BRA) for current conditions and a Climate Change Assessment (CCA) for future warming scenarios. Under the BRA, 12 species (26.1%) were classified as high risk. This figure increased to 16 species (34.8%) under the CCA, demonstrating the heightened threat posed by climate change. Four species—goldfish (Carassius auratus), common carp (Cyprinus carpio), vermiculated sailfin catfish (Pterygoplichthys disjunctivus), and leopard pleco (P. gibiceps)—were identified as very high-risk. The analysis reveals that climate change elevates the risk scores for 74% of the species studied. The findings underscore the necessity of integrating climate-aware protocols into national biosecurity strategies to protect vulnerable freshwater ecosystems and support SDG Target 15.8, which calls for measures to control invasive alien species. The report recommends a precautionary ‘whitelist’ import system based on robust, climate-integrated risk screening to ensure responsible trade practices in line with SDG 12 (Responsible Consumption and Production).

1.0 Introduction

The global proliferation of aquatic invasive species represents a significant impediment to achieving key Sustainable Development Goals, particularly SDG 14 (Life Below Water) and SDG 15 (Life on Land). The ornamental pet trade has been identified as a major pathway for introducing non-native species, which can disrupt ecosystem integrity, reduce biodiversity, and compromise essential ecosystem services. This issue is exacerbated by climate change, directly challenging the objectives of SDG 13 (Climate Action), as rising water temperatures create more favorable conditions for the establishment of thermophilic invasive species.

Türkiye, a nation with unique ichthyofaunal diversity, is situated in a climate-change hotspot and is highly vulnerable to biological invasions. The country’s freshwater ecosystems already host 34 non-native fish species, 19 of which are self-sustaining. Recent evidence confirms that releases from the aquarium trade are a primary introduction vector, with several ornamental species having established breeding populations. This study addresses a critical gap by applying a climate-integrated risk assessment to popular aquarium fish imported into Türkiye, providing a scientific basis for policies that align with international conservation and sustainability commitments.

1.1 Objectives

The primary objectives of this report are:

1. To evaluate the invasion risk of 46 popular aquarium fish species in Türkiye under current climatic conditions using the Aquatic Species Invasiveness Screening Kit (AS-ISK).
2. To assess the impact of projected climate warming on the invasion risk scores and rankings of these species, thereby informing climate-resilient management strategies consistent with SDG 13.
3. To provide evidence-based recommendations for strengthening national biosecurity frameworks to mitigate the threats posed by invasive species, directly supporting SDG Target 15.8.

2.0 Methodology

A comprehensive risk screening was conducted on 46 non-native ornamental fish species traded in Türkiye. The selection was based on consultations with key stakeholders to ensure market relevance. The assessment utilized the Aquatic Species Invasiveness Screening Kit (AS-ISK), a decision-support tool designed to identify potentially invasive species.

2.1 Risk Assessment Framework

• Basic Risk Assessment (BRA): Each species was evaluated against 49 questions covering biogeography, invasion history, and biological/ecological traits under current environmental conditions.
• Climate Change Assessment (CCA): An additional six questions were used to adjust the BRA score based on predicted impacts of future climate scenarios on introduction, establishment, dispersal, and impact. This forward-looking approach is vital for developing adaptive policies aligned with SDG 13.
• Risk Categorization: Species were classified as low, medium, or high risk. A threshold to distinguish between medium and high risk was established through Receiver Operating Characteristic (ROC) curve analysis, ensuring robust and calibrated outcomes. An ad hoc threshold (score ≥ 30) was used to identify ‘very high-risk’ species requiring immediate management attention.

3.0 Results

The risk screening revealed a substantial and increasing threat of invasion from ornamental fish, amplified by climate change. The ROC curve analysis yielded an Area Under the Curve (AUC) of 0.8438, indicating excellent discriminatory power for the assessment tool.

3.1 Basic Risk Assessment (BRA) – Current Conditions

Under current climate conditions, the BRA classified the 46 species as follows:

• High Risk: 12 species (26.1%)
• Medium Risk: 28 species (60.9%)
• Low Risk: 6 species (13.0%)

This initial assessment highlights a significant existing threat to Türkiye’s freshwater biodiversity, challenging the conservation goals of SDG 14 and SDG 15.

3.2 Climate Change Assessment (CCA) – Future Conditions

When future climate scenarios were integrated, the invasion risk profile shifted significantly, demonstrating the critical impact of climate change on biodiversity threats.

• High Risk: 16 species (34.8%) – an increase of four species from the BRA.
• Medium Risk: 28 species (60.9%)
• Low Risk: 2 species (4.3%)

The climate adjustment resulted in an increased risk score for 34 species (74%). Seven species received the maximum possible risk increment (+12), indicating a severe amplification of their invasive potential under future warming.

3.3 Very High-Risk Species

Four species were identified as posing a very high risk of invasion under both current and future climate scenarios. These species demand priority action to prevent further ecological damage and support the restoration targets of SDG 15.

1. Carassius auratus (Goldfish)
2. Cyprinus carpio (Common Carp)
3. Pterygoplichthys disjunctivus (Vermiculated Sailfin Catfish)
4. Pterygoplichthys gibbiceps (Leopard Pleco)

4.0 Discussion

The findings confirm that climate change will substantially increase the invasiveness of ornamental fish in Türkiye, making temperate regions more suitable for tropical species. This trend directly threatens the country’s unique freshwater biodiversity and undermines progress toward SDG 14 and SDG 15. The validation of the high-risk status for species already established in Türkiye (e.g., Carassius auratus, Pterygoplichthys disjunctivus) confirms the predictive accuracy of the AS-ISK tool.

The reclassification of species like Poecilia sphenops from medium to high risk under the CCA highlights the inadequacy of static assessments. Dynamic, climate-aware screening is essential for proactive management. Conversely, the nuanced assessment of species like Pangasianodon hypophthalmus, whose risk was downgraded due to specific reproductive requirements absent in Türkiye, demonstrates the tool’s analytical sophistication. However, the overall trend points to an urgent need for enhanced regulatory oversight of the ornamental fish trade to align with principles of SDG 12 (Responsible Consumption and Production).

While warming may expand suitable habitats, increasing water stress in regions like Central Anatolia—a critical issue related to SDG 6 (Clean Water and Sanitation) and SDG 13—could simultaneously limit the dispersal of both native and invasive species by fragmenting aquatic ecosystems. This complex interplay requires integrated management strategies that consider both climate change and water resource management.

5.0 Conclusion and Recommendations

The invasion risk posed by the ornamental fish trade to Türkiye’s freshwater ecosystems is significant and is projected to worsen with climate change. Static risk assessments are insufficient for addressing future threats. To safeguard biodiversity and align with the Sustainable Development Goals, a proactive and adaptive management framework is imperative.

5.1 Recommendations for Policy and Management

The following actions are recommended to support the achievement of SDG 15.8, SDG 14, SDG 13, and SDG 12:

1. Adopt a Dynamic, Climate-Aware Risk Assessment Protocol: National authorities should formally integrate the AS-ISK with its CCA component into biosecurity and import regulations. Assessments should be periodically updated to reflect new climate projections and trade data.
2. Implement a Precautionary ‘Whitelist’ System: Shift the regulatory burden from prohibiting known high-risk species (‘blacklist’) to permitting only those species demonstrated to be low-risk through a thorough AS-ISK screening. This approach promotes SDG 12 by ensuring importers are accountable for the environmental safety of their products.
3. Enhance Monitoring and Early Detection: Establish a national monitoring program for high-risk aquatic habitats, such as thermal springs and effluent canals. Utilize modern techniques like environmental DNA (eDNA) and citizen science platforms to facilitate early detection and rapid response.
4. Strengthen Public Awareness and Stakeholder Engagement: Launch targeted campaigns to educate aquarium owners, importers, and retailers about the ecological risks of releasing non-native species and promote responsible pet ownership.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 15: Life on Land: This is the most central SDG. The article directly addresses the threat of aquatic invasive alien species to freshwater biodiversity and ecosystems in Türkiye. It focuses on assessing invasion risk to protect native species and habitats, which aligns with the goal of halting biodiversity loss and protecting terrestrial and inland freshwater ecosystems.
• SDG 13: Climate Action: This goal is a primary focus of the study. The article’s core analysis is how climate change (specifically, warming waters) is “expected to increase the invasiveness of non-native aquarium fish.” It explicitly integrates regional warming scenarios into its risk assessment, advocating for climate-aware policies to combat future threats.
• SDG 14: Life Below Water: While SDG 14 primarily focuses on marine and coastal ecosystems, its principles of conserving and sustainably using aquatic resources are relevant. The article’s discussion on the “global spread of aquatic invasive species” and their devastating consequences on aquatic ecosystems connects to the broader aims of this goal, even though the specific context is freshwater.
• SDG 6: Clean Water and Sanitation: This goal is connected through its target to protect and restore water-related ecosystems. The article notes that invasive species like cyprinids can cause “increasing turbidity, dislodgement of macrophytes, and alteration of nutrient cycling,” which directly degrades the health and quality of freshwater ecosystems (rivers, reservoirs, springs) that this SDG aims to protect.
• SDG 12: Responsible Consumption and Production: The article identifies the “global ornamental pet trade” as a “major and increasingly recognised pathway for the introduction of freshwater fishes.” This multi-billion-dollar industry represents a pattern of consumption and global trade. The study’s call for a “‘whitelist’ import system” and better regulation directly relates to achieving more sustainable management of this trade to prevent its negative environmental impacts.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. SDG 15: Life on Land

   • Target 15.8: “By 2020, introduce measures to prevent the introduction and significantly reduce the impact of invasive alien species on land and water ecosystems and control or eradicate the priority species.” The entire study is an application of a risk-screening tool (AS-ISK) designed to identify and prioritize potentially invasive species to inform preventative measures. The recommendation for a “‘whitelist’ import system” is a direct policy measure to achieve this target.
   • Target 15.5: “Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and… protect and prevent the extinction of threatened species.” The article highlights that invasive species “outcompete native species for resources, disrupt food webs, degrade habitats, and hybridize with native species,” directly contributing to habitat degradation and biodiversity loss that this target seeks to prevent.

2. SDG 13: Climate Action

   • Target 13.2: “Integrate climate change measures into national policies, strategies and planning.” The article’s primary conclusion is that “static risk assessments are inadequate” and calls for the integration of climate change scenarios into national biosecurity policies. The use of the Climate Change Assessment (CCA) is a practical example of how to integrate such measures into planning.
   • Target 13.1: “Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.” The study treats the increased risk of biological invasions as a climate-related hazard. By providing a “dynamic, climate-aware” risk protocol, it aims to build adaptive capacity to manage this emerging threat.

3. SDG 6: Clean Water and Sanitation

   • Target 6.6: “By 2020, protect and restore water-related ecosystems, including… wetlands, rivers… and lakes.” The article details how invasive fish like Pterygoplichthys spp. cause “habitat degradation, accelerated erosion, and increased sedimentation” through their burrowing activities, directly impacting the physical structure and health of the freshwater ecosystems this target aims to protect.

4. SDG 12: Responsible Consumption and Production

   • Target 12.2: “By 2030, achieve the sustainable management and efficient use of natural resources.” The ornamental fish trade is framed as a use of biological resources. The article’s analysis of the trade’s role in introducing high-risk invasive species points to an unsustainable pattern that requires better management, as proposed through risk screening and import controls.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

• Risk Assessment Scores (BRA and CCA): The article uses the Aquatic Species Invasiveness Screening Kit (AS-ISK) to generate a Basic Risk Assessment (BRA) score and a Climate Change Assessment (CCA) adjusted score. These scores are quantitative indicators used to measure the potential invasion risk of a species, directly supporting Target 15.8.
• Proportion of High-Risk Species: The study provides clear metrics, such as “The BRA classified 12 species (26.1%) as high risk, while under the CCA, this rose to 16 species (34.8%).” This percentage serves as an indicator of the overall threat level from the ornamental fish trade and can be tracked over time.
• Number of Established Invasive Alien Species: The article mentions that in Türkiye, there are “34 non-native freshwater fish species, of which approximately 19 are now self-sustaining.” This number is a direct indicator of the current state of biological invasions and can be used as a baseline to measure the effectiveness of future prevention policies (Target 15.8).
• Adoption of Climate-Integrated Policies: The article strongly advocates for “dynamic, climate-aware risk protocols” and a “‘whitelist’ import system.” The adoption of such policies by national authorities (e.g., the Turkish ministry) would be a key indicator of progress towards integrating climate change into national planning (Target 13.2).
• Monitoring Data (e.g., eDNA): The recommendation to use “empirical validation via field and eDNA monitoring” implies that data from these monitoring activities (e.g., presence/absence of invasive species in new locations) can serve as an indicator for tracking the spread of invaders and the effectiveness of control measures.

4. Table of SDGs, Targets, and Indicators

Source: nature.com