Learn & Explore/Habitats/Streams/Alien Species

Alien Species

Alien species are non-native plants and animals that threaten Hawaii’s streams.

Early Alien Species in Hawaiian Waters

  • Today, over 50 alien species — including fishes, invertebrates, reptiles, amphibians, and plants — are established in Hawaiian streams and reservoirs.
  • Many species were intentionally released to become established and potentially improve life in Hawai‘i.
  • Other species were dumped without considering consequences.

Historical Introductions

  • Some of the first aquatic introductions occurred in the 1800s, brought by early Asian immigrants.
  • Early species included: to escape predators
    • Chinese catfish
    • Rice paddy eel
    • Soft-shell turtle
    • Carp
    • Goldfish
    • Japanese weather fish (dojo)
  • Most were introduced for food, while a few, like goldfish, were for ornamental purposes.
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The History of Alien Species in Hawaiian Streams

Early To Mid-1900s Introductions

  • Topminnows (medaka or tabai) were released in streams and reservoirs for mosquito control.
  • Tilapia species were introduced to:
    • Control weeds in irrigation systems for sugar plantations
    • Serve as baitfish for aku (skipjack tuna) fishing
  • Gamefish like largemouth bass, smallmouth bass, trout, and tucunare were introduced for sport and recreation.
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1970s – Environmental Awareness

  • The rise of the environmental movement led to a new appreciation of Hawai‘i’s unique native fauna and flora.
  • Focus shifted from “improving” streams to preserving native species.
  • Government-sponsored introductions of alien species stopped, and import requests were strictly regulated.
  • By this time, around 70 aquatic alien species had been intentionally released, with more than half established in streams and nearshore waters.
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1980s–1990s – New Alien Species

  • More alien species appeared in streams and reservoirs, mostly from aquarium and aquaculture industries, including:
    • Convict cichlid, Midas cichlid, Johanni cichlid, Jewel cichlid
    • Suckermouth catfish, Armored catfish, Stickfish
    • Apple snail, Grass shrimp
  • Asiatic clam was likely smuggled in by Asian immigrants for food and is now common in streams, reservoirs, and taro patches on Kaua‘i, Maui, and O‘ahu.
  • A goby species may have been introduced via a ship’s ballast tank.
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Impacts of Alien Species on Native Streams

  • Alien species are having noticeable impacts on native stream animals and habitats.
  • Suckermouth catfish and crayfish:
    • Dig holes in stream and reservoir banks
    • Cause erosion
    • Increase silt in the water
  • Smallmouth bass:
    • Voracious predators
    • Feed on native ‘o‘opu (gobies) and ‘ōpae (shrimp)
  • Even seemingly harmless species, like guppies and swordtails, can carry parasites that infect native ‘o‘opu
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