Breeding biology of a non-diadromous galaxiid, Galaxias vulgaris Stokell, in a New Zealand river

In the Glentui River, Canterbury, New Zealand, Galaxias vulgaris Stokell spawned in late winter and early spring (from July to September), the onset of spawning being temperature-dependent. No females matured in their first year, but 95 and 68 % of age 0+ males were mature in consecutive years. With the exception of one female, all fish aged 1 + and older spawned. In mature fish, overies reached nearly 23%, and testes 11%, of somatic weight. Maturity in males depended on size, whereas in females, age appeared to be the major factor affecting maturity. Recruitment eggs for next season's spawning were distinct from primary oocytes soon after the ripe eggs were shed. Egg numbers varied between 284 and 1911 per fish, and weight was the best indicator of fecundity. Sex ratios of whole samples were not significantly different from 1 : 1, but ratios of potential spawners revealed an excess of males, due mainly to the presence of age 0 + fish. Age0+ males probably play an important role in adverse conditions and act as a form of insurance by significantly increasing the proportion of ripe males, thereby ensuring that all eggs are fertilized. The nest, egg mass and behaviour during the spawning period are described. More than one female may lay eggs in each nest and it is probable that each egg mass receives sperm from more than one male. It is suggested that the presence of fewer and larger eggs in G. vulgaris , compared with the diadromous galaxiids, is the result of a more precise fertilization process.