WHAT IS FISH STOCKING?
Fish stocking is the practice of raising fish in hatcheries—indoor facilities where fish eggs are artificially bred and hatched, and the young fish are raised in a controlled environment—and then releasing them into lakes, ponds, rivers, and streams. State and local agencies do this to introduce new species for sport and to increase the number of people purchasing fishing licences, as some of the agencies’ funding comes from these sales.
Routine fish stocking threatens biodiversity and native trout, 1 results in extremely high fish mortality, 2 and continues without adequate ecological impact studies on Massachusetts ecosystems.
- Displace native, wild fish from their habitats
- Introduce diseases and parasites
- Disrupt the natural balance of aquatic ecosystems
- Have high mortality rates
Redirecting funding toward habitat restoration, science-based conservation, and accessible, hands-on, community-based education would better protect Massachusetts rivers and lakes and align with the state’s biodiversity mandate.
Why BEAT is taking a stand
Routine non-native fish stocking undermines biodiversity, wastes resources, and distracts from the work that truly protects rivers and native species.
Ending the practice would align Massachusetts fisheries and wildlife management with the Governor’s biodiversity mandate and reflect science-based stewardship.
We believe it is time to move beyond stocking fish destined to die and invest instead in healthy ecosystems that sustain life for generations.
Watch our in-depth webinar that provides a science-based overview of fish stocking in Massachusetts.
YOUR VOICE MATTERS.
You can make a difference by urging state officials to rethink fish stocking in Massachusetts.
Reach out as an individual or on behalf of an organization—every call, email, and letter counts.
ASK THEM TO STOP STOCKING YOUR LOCAL WATERBODY! Refer to/use our email templates for individuals and for organizations/groups
It Works!
After more than 60 people emailed and wrote to the MassWildlife Board, stocking in the upper Deerfield River ended in early 2025.
Public pressure can lead to real science-based changes in how we manage wild fish, their natural habitats, and our native ecosystems.
And check out BEAT’s pamphlet on this issue & stop by our center to pick up a few to share!
View the PamphletStocked Massachusetts Waters
This interactive map was created using data available on MassWildlife’s page on Mass.gov. Click the map legend to see what each color indicates. You can also click a specific point to see which waterbody it is, the town it’s in, and whether it’s stocked in spring, fall, or both seasons.
Fish stocking is ecologically unsound, produces pollution & thwarts biodiversity
The practice of raising hundreds of thousands of fish in hatcheries and repeatedly introducing them into Massachusetts waterways is ecologically unsound and environmentally harmful. Hatchery operations generate pollution, including greenhouse gas emissions, wastewater discharge, and nutrient loading into rivers and streams.3,4,5,6
Stocking introduces large volumes of fish biomass into aquatic systems. The resulting stress, starvation, and rapid mortality of stocked fish contribute to organic waste and nutrient inputs, which can degrade water quality and disrupt ecosystem function.2,7,8
Fish stocking conflicts with Governor Healey’s Biodiversity Mandate. Under Governor Healey’s Biodiversity and Conservation Mandate, all executive departments and agencies are required to support comprehensive biodiversity conservation goals.9As stated in the mandate: “All executive department offices and agencies shall support the Commissioner of the Department of Fish and Game in this comprehensive review of biodiversity conservation goals.” Routine stocking of non-native fish is fundamentally at odds with this mandate. Rather than protecting biodiversity, stocking introduces non-native species that alter food webs, increase competition, and weaken native ecosystems.10,11
This conflict has been underscored by statements from Department of Fish and Game leadership. In an interview with Mass Audubon, Commissioner Tom O’Shea stated:
Eastern brook trout provide a clear, local example of the responsibility described above. As a native coldwater species of conservation concern in Massachusetts, brook trout are among the 450 species in the Commonwealth that Commissioner O’Shea has acknowledged are threatened or at risk.
Because brook trout are experiencing documented population decline, they fall squarely within the category of species that require targeted conservation action. Under the Commonwealth’s biodiversity and conservation framework, species in decline warrant clear, species-specific management measures—whether through formal conservation plans or enforceable management standards—with defined objectives, monitoring benchmarks, and adaptive strategies incorporated into agency operations.
Continuing routine non-native fish stocking in waters that still support brook trout conflicts with this responsibility, particularly in the absence of enforceable protections designed to prevent further population decline.
Brook Trout Populations Overlap With State Stocking
Map Note: This interactive map was created using data from MassWildlife’s trout stocking report and catchment and patch scale assessments from the Eastern Brook Trout Joint Venture (EBTJV). EBTJV uses a predictive model to estimate the presence of eastern brook trout in areas upstream of sampled locations. Across the region—from Georgia to Maine—this includes hundreds of thousands of small catchments (typically 1–2 km in length), many of which have predicted salmonid occupancy. Given the scale of the dataset, it is not feasible to verify each catchment through fieldwork or manual review. As a result, these data are best used to understand broad, landscape-level patterns rather than conditions within specific stream reaches.
Native Brook Trout are in decline, and stocking adds pressure
It is undisputed that Eastern Brook Trout populations are declining. Across its native range, brook trout populations are estimated to have declined by approximately 50% over the last 25 years, due to habitat loss, invasive species, and climate change.17,18 Brook trout depend on cold, clean, flowing water and are highly sensitive to warming temperatures.
As climate change increases temperature variability, brook trout are increasingly outcompeted by non-native brown trout, which can tolerate warmer and more variable conditions.1,19,20 Stocking brown trout into systems that still support brook trout imposes competitive pressure and risks accelerating declines in native populations. While MassWildlife has conducted some brook trout studies, we believe those studies did not meet the conditions necessary for drawing valid conclusions about the impacts of stocking on native populations.
Non-native fish disrupt food chains & ecosystem function
Non-native fish can have significant impacts on aquatic food chains, including:
- Reducing zooplankton and phytoplankton populations 13
- Impacts to invertebrate communities 2
- Increasing turbidity, which harms photosynthetic aquatic plants 13
- Disrupting the trophic cascade that supports healthy ecosystems 13
These disruptions affect not only native trout diets, but can affect both aquatic and terrestrial ecosystems—including insects, plants, birds, and downstream species.14
In addition, non-native fish can indirectly support other invasive species.1516 For example, stocking can bolster populations of the Chinese mystery snail, an invasive species present in Massachusetts that outcompetes native snails and further disrupts food webs and ecosystem balance.
Hybridization weakens wild populations
Stocking weakens wild populations at the genetic level; if hatchery fish interbreed with wild populations, the result is hybridization—the process by which two different species successfully breed and produce offspring— which weakens the genetic adaptations that wild fish have developed over generations.
This loss of local adaptation reduces:
- Fitness
- Disease resistance
- Reproductive success
- Long-term survival
For native trout already stressed by climate change and habitat degradation, genetic dilution further undermines population resilience. Stocking doesn’t just add fish, it can erode the genetic strength of wild populations.21,22,23
Hatchery trout are raised knowing most will die shortly after release
Stocked fish experience extremely high mortality rates shortly after release. Studies routinely document mortality rates ranging from 67.5% to over 90% within weeks to months.
Examples include:
- A New York study documenting 99.9% mortality over two years 2
- A Housatonic River study that failed to recapture 67.5% of fish released in the fall, suggesting high mortality 24
- A MassWildlife study on the Swift River, showing that 50% of rainbow trout and 33% of brown trout were unaccounted for just one week after stocking 25
MassWildlife stocks nearly 500,000 trout each year, and by the department’s own admission, almost all of these fish die shortly after release. 26 In numerous water bodies where stocking has occurred, non-native species populations have become established, with potential long-term ecological consequences.
One contributing factor to high mortality is competition: stocked fish are often outcompeted by wild fish and are poorly equipped to forage or survive in wild conditions. 27
The high volume of fish mortality following stocking raises concerns about nutrient pollution. Decaying fish biomass can release nitrogen into waterways, contributing to eutrophication and oxygen depletion. Elevated nitrogen levels can lead to algal blooms, reduced dissolved oxygen, and degraded aquatic habitat; these conditions further harm native species and overall ecosystem health. 28,29
Resources should be redirected toward habitat, restoration, and education
Funding and resources devoted to hatcheries, fish production, transportation, and repeated stocking events could instead be invested in strategies proven to support long-term ecosystem health. The Department of Fish and Game should redirect resources toward proven conservation strategies, including:
- Creating and restoring habitat that supports brook trout and ecologically aligned species
- Dam removal and improving stream connectivity
- Enhancing cold-water refuges and riparian shading
- Education, outreach, and public engagement; supporting partnerships among agencies, nonprofits, and local stakeholders to address regional ecological threats
- Research and monitoring to guide adaptive management
- Restoring populations impacted by habitat modification, invasive species, or other disturbances
These approaches are consistent with recommendations from the Eastern Brook Trout Joint Venture and other conservation strategy working groups, and align with Massachusetts’ biodiversity goals to protect native species across their historic range. Habitat restoration lasts. Stocking does not.
No Monitoring, No Accountability
There is inadequate study and oversight of fish stocking and no comprehensive monitoring in Massachusetts. Regardless of the millions of dollars funding the practice, and despite the scale of the program, MassWildlife has not conducted or published comprehensive studies on:
- The effects of stocking on native brook trout populations
- The impacts on aquatic macroinvertebrates and primary producers, which form the foundation of freshwater food webs
- Public perception of fish stocking (as opposed to biodiversity-supportive investment like habitat restoration, youth education, etc.)
Because research elsewhere shows significant harm to native fish, amphibians, and invertebrate communities, the absence of Massachusetts-specific studies represents a serious gap in oversight and accountability. MassWildlife has not adequately demonstrated that its practices do not cause ecological harm.
The agency has not demonstrated sufficient public support for routine non-native fish stocking. BEAT has been interviewing anglers, and conversations so far suggest that many anglers prefer native fish and healthy habitat over put-and-take stocking programs. Without transparent public input or documented support, continuing this practice raises questions about whose interests are being served.
What Experts and Conservation Groups Say
Scientific consensus strongly cautions against routine fish stocking:
- Approximately 83% of published research on fish stocking finds negative impacts on wild populations.30
- Conservation organizations including the Conservation Law Foundation and the Center for Biological Diversity have advocated for ending or sharply limiting the practice.
- Angler organizations, such as Trout Unlimited, have called for reducing or ending stocking in favor of habitat-based management.31
Further Reading
Additional authoritative resources and peer-reviewed research worth checking out:
Open the list
Division of Fisheries and Wildlife to cease stocking rainbow trout in Upper Deerfield River
Read →Non-native fishes homogenize native fish communities and reduce ecosystem multifunctionality in tropical lakes over 16 years
Read →Ecological impacts of non-native freshwater fishes
Read →Non-native species drive the global loss of freshwater fish beta-diversity
Read →The trouble with fish stocking
Read →Invasive predator influences habitat preferences in a freshwater fish
Read →Email Templates
Open Templates
How to Use These Templates
- Choose the template that best reflects your situation (individual resident or organization/group)
- Copy and paste it into your email — Don’t forget to also copy and paste the subject line!
- Replace the bracketed sections with your information and personalize the message if you’d like.
- Email it to DFG Commissioner Tom O’Shea, tom.oshea@mass.gov, and the MassWildlife Board, Mass.Wildlife@Mass.Gov
Tip: Personal messages are especially powerful — just a sentence or two about why this issue matters to you can say a lot.
Template for individual resident
[ Subject: ] Please Stop Stocking [Waterbody Name]</mark[Date]
Dear Commissioner O’Shea and Members of the Massachusetts Fisheries and Wildlife Board,
I am a resident of [Town/City], and I care deeply about [Waterbody Name] in my community. I am writing to ask that MassWildlife stop stocking fish in this waterbody.
I care about this issue because:
- [I value protecting native fish and wildlife.]
- [I value healthy, natural ecosystems and believe our lakes, rivers, and streams should be managed to protect native species and biodiversity.]
- [Public waters should be managed for long-term ecological health, not short-term recreation.]
- [Our natural ecosystems and native wildlife populations deserve to be managed based on transparent, science-based conservation.]
- [Taxpayer-funded programs such as fish stocking should not harm biodiversity and water quality.]
- [Personal reason – e.g., I swim/paddle/fish here and want to see it thrive naturally.]
Please stop stocking in [Waterbody Name] and instead prioritize the protection and restoration of healthy, self-sustaining freshwater ecosystems.
Thank you for your attention to this matter.
Sincerely,
[Full Name]
[Street Address, Town]
[Email Address]
Template for organization/group
Subject: Request to End Fish Stocking in [Waterbody Name]
[Date]
Dear Commissioner O’Shea and Members of the Massachusetts Fisheries and Wildlife Board,
On behalf of [Organization Name], we are writing to request that MassWildlife cease fish stocking in [Waterbody Name].
Our organization represents [number]residents/members who are investing in the ecological health and long-term stewardship of this waterbody. As a [lake association / watershed group / conservation organization], we prioritize biodiversity, water quality, and sustainable management practices and would like to see MassWildlife do the same.
Fish stocking disrupts aquatic ecosystems and can cause native species to decline, adding ecological stressors to ecosystems already strained due to climate change. These impacts are inconsistent with our shared goal of protecting and stewarding resilient rivers and lakes.
We respectfully request that stocking in [Waterbody Name] be suspended and that management decisions prioritize ecological integrity, transparency, and science-based evaluation of impacts.
Sincerely,
[Full Name]
[Title]
[Organization/Group Name]
[Email Address]