The brown bullhead - our very own catfish pest

Author: Darren Stevens

First published in Aquarium World February 2014

brown bullhead © Noel Burkhead

Although many aquarists will have a common bristlenose or Corydoras catfish in their tropical tanks there are no native freshwater catfish (Siluriformes) in New Zealand. In contrast, our Australian neighbours have about 18 freshwater catfish species. We do however have an introduced species, the brown bullhead (Ameiurus nebulosus) a stocky dark brown to greenish-olive catfish with 4 long whisker-like barbels, speckled with gold, pale olive, and grey. Brown bulheads are generally found in slow flowing, often weedy, streams and around the sandy shallow margins of lakes and lagoons. In New Zealand they commonly grow to 30cm but have been reported to grow to about 45cm and 2kg. They eat a wide range of food including freshwater insects, snails, crustaceans including koura, plant material, detritus, and small fish. They are a problem in our waters as they compete with, and eat, native species, including small native fish and koura. They also reduce water quality by stirring up mud.

In New Zealand brown bullheads are not well studied although they appear to be fast growing, reaching 8cm in their first year, and 33cm by their fourth year, and they may live for up to 8 years. They mature at age 2 or 3 (at about 180-200mm TL) and pair up and spawn during spring. They lay several hundred to over 6000 golden eggs in a shallow depression in mud or sand. Initially both sexes guard the eggs and young but as the young develop it is generally the male that will guard the young for several weeks.

Brown bullheads were introduced to New Zealand from California in 1877 and initially became established in the lower Waikato River and in Lake Mahinapua near Hokitika. They are very adaptable and are able to survive for long periods out of water. Unfortunately this makes them easy to accidentally transfer to new waterways in fyke nets or on boat trailers, and they are now reported from a number of waterways including the Whanganui River, Ruamahanga River, and Lake Taupo. At times they can very abundant with a single overnight fyke set in Lake Taupo catching 639 catfish. To help prevent further spread if you catch a brown bullhead you must kill it immediately. The penalty for possessing a live bullhead catfish is $750.

 References:

McDowall, R. M. (1990). New Zealand Freshwater Fishes: A natural history and guide. Heinemann Reed, Auckland.

Brown Bullhead Catfish – Code of Practice Effective from 1 October 2007. http://www.fish.govt.nz/NR/rdonlyres/333F2B8C-6808-4DD7-868A-B7100F71DDE8/0/Brown_Bullhead_Catfish_Code_of_Practice.pdf

Barnes, G.E.; Hicks, B.J. (2001). Brown bullhead catfish (Ameiurus nebulosus) in Lake Taupo. In: Department of Conservation 2003. Managing invasive freshwater fish in New Zealand. Proceedings of a workshop hosted by the Department of Conservation, 10-12 May 2001, Hamilton. xiv +174 p.

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