New Zealand Journal of Marine and Freshwater Research abstracts

---

Aspects of juvenile rainbow trout (Oncorhynchus mykiss) diet in relation to food supply during summer in the lower Tongariro River, New Zealand

M. DEDUAL

Department of Conservation
Private Bag
Turangi, New Zealand

K. J. COLLIER

Department of Conservation
P.O. Box 10-420
Wellington, New Zealand

Present address: National Institute of Water & Atmospheric Research Ltd, P.O. Box 11-115, Hamilton, New Zealand

Abstract  Invertebrates were collected from the benthos, drift, and stomachs of juvenile rainbow trout (Oncorhynchus mykiss) in different flow environments and at different times of day in the lower Tongariro River in December 1992, to investigate spatial and diel patterns in prey abundance and diet. The benthic and drift communities were dominated numerically by Diptera (both 71%), Oligochaeta (22-23%), and Trichoptera (5% and 2% in the benthos and drift, respectively). Terrestrial invertebrates comprised 3% of the drift. The most common prey in the stomachs of juvenile rainbow trout (44-130 mm fork length) were Diptera (74%), Trichoptera (19%), Ephemeroptera (6%), and some terrestrial organisms. Relative abundances of different invertebrate taxa in the benthos, drift, and stomachs of juvenile rainbow trout were all significantly intercorrelated. Juvenile trout fed selectively on Trichoptera (particularly emerging adults), the ephemeropteran Deleatidium spp., and some Diptera (mostly Maoridiamesa and Aphrophila neozelandica), and avoided Oligochaeta. The stomach fullness index was similar during three periods between dawn and dusk, indicating that feeding activity was continuous. The proportion of Diptera in the diet of small fish was higher than in larger fish and the reverse was observed for the proportion of Trichoptera. Densities of most benthic invertebrate taxa favoured by juvenile trout were highest in medium or fast flowing habitats, suggesting that maintenance of such conditions is important for food production.

Keywords  rainbow trout; Oncorhynchus mykiss; benthic invertebrates; drift; feeding; prey selection; Tongariro River

New Zealand Journal of Marine and Freshwater Research, 1995, Vol. 29: 381-391

0028-8330/95/2903-0381 $2.50/0 (c) The Royal Society of New Zealand 1995

PDF file of entire paper: medium quality (788K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page