Age Composition, Growth and Reproductive Biology of the Salamanderfish Lepidogalaxias salamandroides: A Re-examination

Abstract

This study has determined the age and size compositions, growth rate and reproductive biology of Lepidogalaxias salamandroides using data for fish of known sex and age and the monthly trends exhibited by various gonadal variables, including the sizes and stages of the oocytes. The results resolve conflicting conclusions drawn by other workers concerning certain aspects of the biology of this freshwater species and expands our knowledge of this teleost. Our results are based on data derived from samples collected from small, ephemeral acidic pools in south-western Australia in 22 consecutive months. Although ca. 78% of the fish caught belonged to the 0+ age class, substantial numbers of the 1+ and 2+ age classes and some 3+ and 4+ fish were caught. Spawning occurs between late May and late August, with peak activity in late July and early August. During the first year of life, growth is initially rapid, but then ceases in the weeks immediately prior to and during the period when the habitat becomes dry and fish aestivate, before recommencing in autumn as the pools again become filled with water. The growth coefficient (K) in the von Bertalanffy growth equation was lower for females (0.63) than males (1.28), reflecting the greater growth undergone by females after the first year of life. Maturity was attained by ca. 28% of the females and ca. 26% of the males that reached the end of their first year of life and by all fish that reached the end of subsequent years of life. The L₅₀s for females and males at first maturity were 43.2 and 38.6 mm TL, respectively. The mean fecundity was only 82.4, reflecting a combination of a small body size and a relatively large egg (diameter=1.8 mm). Lepidogalaxias salamandroides is a multiple spawner, which increases the chances of some eggs and newly-hatched embryos encountering a period of favourable environmental conditions during the spawning period, which is characterised by bouts of heavy rainfall. The ratio of females to males was essentially parity in the 0+ and 1+ age classes and in all age classes collectively. When testes commence maturing for the first time, the anal fin of males starts to become modified to form a structure that facilitates the transfer of sperm to the female, and it remains modified throughout the rest of life.