Early development and growth of the eastern rainbowfish, Melanotaenia splendida splendida (Peters). II. Otolith development, increment validation and larval growth

Abstract

A method of preparing and interpreting the microstructure of otoliths of the eastern rainbowfish, Melanotaenia splendida splendida, was developed and used to validate the periodicity of increment formation. Otoliths were collected from laboratory-reared M. s. splendida of known age. The sagittal otolith was preferred for ageing because resolving the earliest increments was easier than in the lapillus during an early slow-growth period, up to 15 days after hatching. Increments formed in the sagittae before hatching, and a distinct discontinuity was visible in the otolith sections at a time corresponding to hatching. Another discontinuity occurred at the time of yolk-sac absorption, when larvae became completely reliant on exogenous feeding. After this, increments were clear, regularly spaced and easily resolved. Linear relationships were found between fish size and sagittal length, breadth and perimeter. Observations of the otolith sections confirmed that the increments in sagittae of M. s. splendida were laid down daily. The information provided here enables growth and mortality rates of M. s. splendida to be measured, providing a useful tool for monitoring the impacts of contaminants in tropical Australian waters.