Giant Bully

Distribution in the Styx River

Giant bullies are found in the lower to middle reaches of the Styx River. There are four records of this species recorded downstream of  Main North Road, however this reach is fished very infrequently, consequently this fish species may be more common than indicated. 

Biology

Little is known about the biology of the giant bully, which is the largest of the freshwater bully species. It is thought giant bully spawn in the lower reaches of rivers. The presence of gravid fish in the Waimakariri during late spring and summer spawning suggests that they spawn during this period (Eldon & Kelly 1985). After the giant bully eggs hatch,  it is thought that the larvae spend some time at sea (McDowall 1990).

Estuarine netting studies have revealed a complete lack of very small giant bullies. The smallest giant bullies caught from the Waimakariri River were over 80 mm long (Eldon & Kelly 1985). This is broadly similar in size to the smallest giant bullies from the Kaikanui Estuary (Jellyman et al. 2000). It is possible that these fish enter freshwater at a much older age than other bullies, or more plausibly they enter as small juveniles with common bullies, and the giant bullies cannot be distinguished from the common bullies.

The largest specimen recored from the Styx River is 202 mm long, and caught just above the tide gates. The largest specimen recorded nationwide was 228 mm long, and recorded from the Kakanui Estuary. These large bullies may live for up to 10 years with growth slowing in the larger fish to about 10 mm per year (Jellyman et al. 2000). Studies would indicate that they spawn only once a year during the summer months when they lay thousands of eggs.

References:

• Eldon, G. A.; Kelly, G. R. 1985. Fishes of the Waimakariri River Estuary. New Zealand Ministry of Agriculture and Fisheries, Christchurch. Fisheries Environmental Report  No. 56. 59 p.
• Jellyman, D. J.; Glova, G. J.; Sagar, P. M.; Sykes, J. R. E. 1997: Spatio-temporal distribution of fish in the Kakanui River estuary, South Island, New Zealand. New Zealand Journal of Marine and Freshwater Research 31: 103-118.
• Jellyman, D. J.; Sagar, P. M.; Glova, G. J.; Sykes, J. R. E. 2000: Age, growth, and movements of giant bullies (Gobiomorphus gobioides) in the Kakanui River estuary, South Island, New Zealand. New Zealand Journal of Marine and Freshwater Research 34: 523-530.
• McDowall, R. M. 1990: New Zealand Freshwater Fishes: A Natural History and Guide. Auckland, Heinemann Reed. 553 p.