Reproductive cycling and fecundity estimation in the upland bully

Abstract

The upland bully is a prolific and widespread member of New Zealand freshwater fish communities that may mature at age 1 (or earlier). It begins spawning in spring, laying as many as eight clutches of eggs over the spring and summer, at periods as brief as 13 days. Ovaries contain two modes of maturing oocytes, so that oogenesis must be continual during the spawning season. This poses difficulties in fecundity estimation, which were solved by captive rearing. The ovoid eggs are about 2 mm long; egg size declines with clutch number during the summer, but increases with fish size. Clutch size varied, in 70 spawnings, from 121 to 880 eggs, with total seasonal fecundity up to >5000 eggs. The production of multiple clutches greatly increases seasonal fecundity and may explain the success of this species in sometimes unreliable or harsh environments.