Age and growth of alpine galaxias (Galaxias paucispondylus Stokell) and longjawed galaxias (G. prognathus Stokell) in the Rangitata River, New Zealand

Abstract

The age and growth of alpine galaxias (Galaxias paucispondylus) and longjawed galaxias (G. prognathus) were determined from samples of fish collected from the Rangitata River, Canterbury, New Zealand. Both species are small (total length up to 112 mm and 87 mm respectively), slender fish with entirely freshwater life histories. Aged from sagittal otoliths, the majority of fish were age 0⁺ and age 1⁺, although alpine galaxias up to age 4⁺ and longjawed galaxias up to age 3⁺ were found. Growth of both species was greatest during their first year of life. Alpine galaxias continued to grow in subsequent years, but fish of ages 2⁺, 3⁺, and 4⁺ were exclusively females. Longjawed galaxias showed little increase in length after their first year of growth, but for all ages > 0⁺ the females were significantly larger than males. Overall, both species are not only similar to each other, but also similar to the dwarf galaxias (G. divergens) and the common river galaxias (G. vulgaris), particularly in terms of their size, habitat, diet, and the age structure of populations.

Keywords:

• alpine galaxias
• Galaxias paucispondylus
• longjawed galaxias
• G. prognathus
• age
• growth
• freshwater fish
• otoliths
• Rangitata River