Diet of giant kokopu, Galaxias argenteus

Abstract

The stomach contents of 105 preserved specimens of giant kokopu, Galaxias argenteus (Gmelin 1789), collected from various locations around New Zealand between c. 1963 and 1994, were used to investigate giant kokopu diet. A total of 76 food taxa, predominantly invertebrates, were identified and categorised as either of aquatic or terrestrial origin from the 91 stomachs that contained food items. Aquatic Trichoptera, Gastropoda, and Hemiptera comprised 29.1, 12.6, and 14.4% by abundance respectively, and terrestrial Coleoptera 12.2% by abundance. Adult terrestrial Coleoptera were the most commonly occurring taxa, and were found in 59% of the stomachs that contained food. Food items of aquatic origin occurred in 94.5% of the giant kokopu stomachs that contained food and comprised 74.9% of the items by abundance. Although fewer items of terrestrial origin were encountered, they nevertheless appeared to be a significant component of the diet, and occurred in 83.5% of the giant kokopu stomachs that contained food, and comprised 25.1% of the items by abundance. Items of terrestrial origin occurred slightly more frequently in giant kokopu from lotic habitats than from lentic habitats. The significance of terrestrial food may be associated with giant kokopu preference for habitats with riparian cover. Fish also appeared to be a significant component of the diet, as 26% of the giant kokopu examined contained fish remains. Giant kokopu are probably best described as generalist feeders, as they utilise a wide range of foods of both aquatic and terrestrial origin.

Keywords:

• giant kokopu
• Galaxias argenteus
• New Zealand
• freshwater fish
• diet
• terrestrial