Invasive Species and Parasites

NH Invasive and Nuisance Species

Aquatic Hitchhiker

Asian Clam:

  • Characteristics 
    • Shells greenish-yellow to brown with thick concentric rings
    • Thick symmetrical shell
    • Up to 2 inches (5 cm) long
    • Inside of shell is smooth and polished with a light purple tinge
  • Found in: 
    • Cobbett's Pond, Windham
    • Canobie Lake, Windham
    • Little Island Pond, Pelham
    • Long Pond, Pelham
    • Sunset Lake (Wash Pond), Hampstead
    • Beaver Lake, Derry
    • Great Pond, Kingston
    • Merrimack River south of Bow
  • Impact: clogging of waterway, resource competition, Promote algae blooms


Zebra Mussel

  • Characteristics: 
    • Named for the striped pattern on its shell - Black or brownish shell with cream or white stripes
    • Shells colors vary widely; some pale or completely white
    • Maximum size less than 2 in (5 cm) long; often less than 1 in
    • Zebra shell is stable when placed on it's flattened hinge side while quagga mussels, lacking a flat side, fall over
    • Valves (shell halves) are symmetrical, forming a straight line when closed whereas the quagga mussel valves are asymmetrical, forming a curved line when the valves are closed
  • Found in: waterbodies all over the state 
  • Impacts: Resource consumption, clog waterways, foul up ship hulls, reduce fish populations

Some species of aquatic wildlife and plants have become unwanted invaders in New Hampshire's waters. Learn more about aquatic invasive species, the laws & rules around possession and use of aquatic species, and what you can do to help stop the invasion!

To prevent the transport of aquatic invasive species, please clean all recreational equipment. Whenever you leave a body of water:

  • RSA 487:16-c mandates that any visible mud, plants, fish, or animals must be removed.
  • RSA 487:16-d mandates that water is drained from equipment (engine water intake systems, bilge, live wells, bait buckets).
  • Clean and dry anything that comes into contact with water (boats, trailers, equipment, etc.)
  • Never release plants, fish or animals into a body of water unless they came out of that body of water.

By preventing the spread of aquatic invasive species you will maintain the high quality of New Hampshire's waters and you will continue to have a place to enjoy your water-based recreational activities (boating, fishing, and swimming), which are popular family-oriented recreational activities that generate more than $1 billion to the state's economy.

Preventing the spread of aquatic invasive species is also the most environmentally sound and cost effective method for battling these alien invaders since once they become established, aquatic invasive species can be impossible to contain and control.

See RSA 207:14 on rules regarding Importing and Releasing wildlife.

See Fis 800 on restrictions regarding Importation and possession of wildlife 

It is not uncommon to catch a freshwater fish that appears "grubby" – infested with pinhead size lumps that are white to yellow or black in color. Many people wonder, is this some new disease? Is the fish safe to eat? This is not a new disease and "grubby" fish may be safely consumed by humans providing they are completely cooked, thereby killing the grubs.

Some fish have only their skin and fins affected. Others are targeted in their musculature and a few may have one or more of their internal organs involved. All of these grubs are dormant encysted larval flatworm parasites (digenetic trematodes).

Cysts, which appear black, are a result of melanin pigment produced by the fish host and deposited around the cysts. This condition is known as disploptomiasis and is caused by a trematode worm in the genus Neascus. Cysts that appear off-white to yellow are caused by a trematode known as Clinostomum marginatum, also known as "yellow grub."

Digenetic trematodes include numerous species of which most are parasitic – that is, they live with a host organism at the expense of the host. These trematodes utilize two or three hosts during their life cycle. Those which cause grubby fish usually take advantage of snails, fish, and fish eating birds and mammals.

Unless the parasitic infection is extreme within a given host, fish grub fluke adults and larvae usually do not appear to seriously harm the host. The snail probably suffers the most due to the intensive reproduction of larval forms within. Occasionally, fish hosts can be harmed when vital organs are involved.

These two species of digenetic trematodes are host specific and luckily humans are not on that list. Grubby fish are safe to handle and may be safely consumed by humans providing they are completely cooked, thereby killing the grubs. We recommend that whenever you keep fish that you dispose of the unwanted parts into the trash and not back into any water body.