From the smallest bubbling brook to the vast expanse of the open ocean, fish inhabit a remarkable range of aquatic environments, making them the most diverse group of vertebrates on our planet.
With approximately 36,000 recognized species—roughly equal to all other vertebrate species combined—fish represent an incredible array of evolutionary adaptations and ecological specializations 2 . Yet beneath the surface of our waters, a silent crisis is unfolding.
Freshwater ecosystems, which cover less than 1% of the Earth's surface, are home to over half of all fish species, and they're facing unprecedented threats 2 4 . Currently, one-third of freshwater fishes are threatened with extinction, and 80 species have already been lost forever 2 . This article explores the ecological importance of fish, the threats they face, and the innovative scientific approaches helping to conserve them for future generations.
The decline of fish populations worldwide stems from a complex web of human-induced pressures. Freshwater ecosystems are particularly vulnerable, facing threats from riparian deforestation, over-extraction of water resources, pollution from industrial, agricultural, and urban sources, and the devastating impacts of climate change 4 .
Deforestation, sedimentation of breeding grounds, and modified water flow threaten freshwater rivers, lakes, and wetlands.
Overfishing beyond sustainable levels and bycatch threaten marine fisheries, particularly for deep-sea species and sharks.
Altered water temperatures, flow regimes, and oxygen levels affect all aquatic ecosystems, especially coral reefs.
Agricultural runoff, industrial waste, and plastic pollution degrade freshwater systems and coastal areas.
| Threat Category | Specific Impacts | Most Affected Ecosystems |
|---|---|---|
| Habitat Loss & Degradation | Deforestation, sedimentation of breeding grounds, modified water flow | Freshwater rivers, lakes, wetlands |
| Overexploitation | Overfishing beyond sustainable levels, bycatch | Marine fisheries, particularly for deep-sea species and sharks |
| Climate Change | Altered water temperatures, flow regimes, oxygen levels | All aquatic ecosystems, especially coral reefs |
| Pollution | Agricultural runoff, industrial waste, plastic pollution | Freshwater systems, coastal areas |
| Invasive Species | Displacement of native species, altered food webs | Island ecosystems, freshwater lakes |
| Loss of River Connectivity | Blocked migration routes, fragmented populations | River systems, particularly affecting migratory species |
Conservation biologists are employing an increasingly sophisticated toolkit to address these challenges, combining traditional approaches with cutting-edge technologies.
This transformative approach detects genetic material that organisms release into their environment, providing a non-invasive, minimally disruptive method for detecting and monitoring species presence 4 .
The preservation of genetic resources through the cryobanking of reproductive cells and tissues provides an insurance policy against extinction for critically endangered species 2 .
Rapid advances in next-generation sequencing technologies help identify genetically distinct populations, understand adaptive potential, and inform conservation breeding programs 2 .
Water samples are collected from aquatic environments using sterile containers to prevent contamination.
Samples are filtered through fine membranes to capture genetic material suspended in the water.
Genetic material is extracted from the filters using specialized laboratory protocols.
Target DNA sequences are amplified using PCR with species-specific primers.
DNA sequences are compared to reference databases to identify species present in the environment.
In 2021, researchers embarked on a comprehensive survey of the Amboaboa River basin in northeastern Madagascar, home to several critically endangered fish species including the cichlids Ptychochromis insolitus (considered extinct in the wild until its rediscovery in 2013) and Paretroplus gymnopreopercularis, along with the Madagascan rainbowfish Rheocles derhami 4 .
The research team employed a dual-method approach, combining traditional fishing techniques with environmental DNA analysis to maximize detection probability 4 . They conducted sampling at 14 distinct locations along 5 rivers in the Sofia drainage and Ambodivato network, chosen based on historical observations of R. derhami and site accessibility 4 .
| Method | Species Detected |
|---|---|
| Traditional Fishing | 15 |
| eDNA (MiFish) | 9 |
| eDNA (Tele02) | 7 |
| eDNA (Riaz) | 6 |
| Combined | 18 |
| Method Category | Specific Approach | Key Findings | Notable Species Detected |
|---|---|---|---|
| Traditional Fishing | Physical capture and identification | Effectively captured diverse species, including invasive aliens and critically endangered endemics | Ptychochromis insolitus, Paretroplus gymnopreopercularis |
| eDNA with Multiple Primers | MiFish, Tele02, and Riaz primer sets | Detected only a fraction of introduced species; struggled to identify some critically endangered endemics at species level | Various introduced species |
| Combined Approach | Integration of both traditional and eDNA methods | Enhanced overall species detection accuracy; provided more comprehensive biodiversity assessment | Multiple endemic and invasive species |
The FAO's 2025 Review of the State of World Marine Fishery Resources offers the most detailed global assessment of marine fish stocks to date, analyzing the biological sustainability of 2,570 individual fish stocks—a major increase from previous assessments 6 .
of all fishery stocks are exploited within biologically sustainable levels 6
of stocks are currently classified as overfished 6
| FAO Fishing Area | Region Name | Sustainably Fished Stocks | Key Observations |
|---|---|---|---|
| Area 67 | Northeast Pacific | 92.7% | Long-term investment and robust management frameworks paying dividends |
| Area 81 | Southwest Pacific | 85.5% | Comprehensive data reveals strong sustainability outlook |
| Areas 48, 58, 88 | Antarctic | 100% | Ecosystem-based management and international cooperation proving effective |
| Area 37 | Mediterranean and Black Sea | 35.1% | Early signs of recovery with 30% fishing pressure reduction since 2013 |
| Area 87 | Southeast Pacific | 46% | Intense fishing pressure, limited institutional capacity |
| Area 34 | Eastern Central Atlantic | 47.4% | Data gaps, fragmented governance hindering sustainability |
Modern fish conservation research relies on specialized methodologies and reagents that enable scientists to study genetic, population, and ecosystem dynamics.
| Reagent/Method | Primary Function | Application in Fish Conservation |
|---|---|---|
| Environmental DNA (eDNA) | Detection of genetic material in water samples | Non-invasive monitoring of species presence, including rare and elusive fish |
| Primer Sets (MiFish, Tele02, Riaz) | Amplification of specific DNA sequences during PCR | Genetic identification of fish species from water samples |
| Cryopreservation Solutions | Long-term storage of genetic material | Establishment of germplasm banks for threatened species |
| Fluorescent In Situ Hybridization (FISH) | Genetic mapping of specific DNA sequences within cells | Chromosome analysis, genetic health assessment in conservation breeding |
| Micro-Raman Spectroscopy | Analysis of molecular composition through light scattering | Detection of illicit conservation treatments in fish products 9 |
Advanced laboratory techniques allow researchers to extract, amplify, and sequence DNA from environmental samples, enabling the detection of species without direct observation.
Conservation efforts increasingly rely on integrating multiple data sources, from traditional field surveys to satellite imagery and genetic databases.
The conservation of fishes represents both an urgent challenge and an extraordinary opportunity to protect global biodiversity. As we have seen, fish populations face unprecedented threats from habitat destruction, overexploitation, climate change, and other anthropogenic pressures. Yet the scientific tools and management strategies needed to reverse these declines are increasingly available and effective.
The FAO's "Blue Transformation" initiative calls for building "more efficient, more inclusive, more resilient and more sustainable aquatic food systems" to increase their contribution to global food security while meeting nutrition requirements and improving livelihoods for a growing population 6 .
The rediscovery of critically endangered fish in Madagascar's Amboaboa River basin offers a powerful symbol of hope—proof that even species presumed lost can persist and potentially recover with dedicated scientific effort and conservation investment. As we continue to develop and refine our conservation toolkit, we strengthen our capacity to protect these vital components of aquatic ecosystems for generations to come. Our success in conserving the incredible diversity of fishes will ultimately determine not just the health of aquatic ecosystems, but the food security, economic stability, and cultural richness of communities worldwide who depend on these remarkable creatures.