Image Credit: Ryan Hagerty, U.S. Fish and Wildlife Service

Aquatics on the DISC list included species that are non-native to Delaware, have the potential for widespread dispersal and establishment, can out-compete other species in the same area, and have the potential for rapid growth, high reproduction rates and establishment in aquatic areas.  Each species was chosen by a committee of experts in environmental and biological sciences after an intensive environmental assessment.

The first Delaware Invasive Species Council (DISC) assessment of invasive plants was conducted in 2003, and followed a protocol developed by NatureServe. However, until now, an invasive species assessment of aquatic species had not been conducted by the Council. In 2019, DISC recognized that the DISC List of Invasive Species needed to be revised and expanded to incorporate aquatic plants, vertebrates, and invertebrates, and terrestrial vertebrates and invertebrates. It was also determined that the NatureServe protocol should be modified to make it more relative to the state of Delaware and non-plant species. This current assessment is based on this modified protocol. Aquatic species experts were contacted in June of 2019 and asked to complete the assessment in an online form. They were provided a list of species to review and were asked to assess those species they were most familiar with. Experts were given five months to review and complete the assessment.

The protocols are documented in the Aquatic Species Assessment Protocol document.

An I-Rank, or invasive rank was determined based on expert responses denoting the level at which a species is invasive in the identified geographic area, in this case, the state of Delaware. These ranks are categorized by high, medium, low, and insignificant. If a species was ranked as high, medium, or low, they are deemed invasive to some degree by the experts and; therefore, are included in the current iteration of the DISC list of Invasive Aquatic Species. Species ranked as insignificant, were added to the DISC Watch List and will be reevaluated in two years. For future revisions to the list, additional species thought to be invasive in Delaware will also be evaluated. In contrast to the previous iterations of the DISC list, the new list includes only two categories – invasive and watch list. Below are the results.

DISC Invasive Aquatics List

SpeciesCommon Name
Anguillicola crassusEel Swimbladder Nematode
Carcinus maenasGreen Crab
Channa argusNorthern Snakehead
Corbicula flumineaAsian Clam
Ctenopharyngodon idella var. triploidGrass Carp (triploid)
Cyprinus carpioCommon Carp
Eriocheir sinensisChinese Mitten Crab
Hemigrapsus sanguineusAsian Shore Crab
Ictalurus furcatusBlue Catfish
Procambarus clarkiiRed Swamp Crayfish
Pylodictis olivarisFlathead Catfish

DISC Invasive Aquatics Watch List

SpeciesCommon Name
Channa maculataBlotched Snakehead
Channa maruliusBullseye Snakehead
Cipangopaludina chinensisChinese Mystery Snail
Crassostrea ariakensisSuminoe Oyster
Crassostrea gigasPacific Oyster
Ctenopharyngodon idellaGrass Carp
Didymosphenia geminataDidymo
Dreissena bugensisQuagga Mussel
Dreissena polymorphaZebra Mussel
Gambusia affinisWestern Mosquitofish
Hypophthalmichthys harmandiLargescale Silver Carp
Hypophthalmichthys molitrixSilver Carp
Hypophthalmichthys nobilisBigheaded Carp
Leuciscus idusIde
Misgurnus anguillicaudatusOriental Weatherfish
Monopterus albusAsian Swamp Eel
Myriophyllum aquaticumParrot’s feather
Neogobius melanostomusRound Goby
Notropis volucellusMimic Shiner
Orconectes rusticusRusty Crayfish
Oreochromis aureusBlue Tilapia
Potamopyrgus antipodarumNew Zealand Mud Snail
Pterois milesCommon Lionfish
Pterois volitansRed Lionfish
Rapana venosaVeined Rapa Whelk
Scardinius erythrophthalmusEuropean Rudd