RHYTHMIC STRUCTURAL AND CHEMICAL-PATTERNS IN OTOLITHS OF THE ANTARCTIC FISH NOTOTHENIA-LARSENI - THEIR APPLICATION TO AGE-DETERMINATION

Sagittal otoliths from N. larseni contain microincremental growth rings which are distinctly visible in otolith sections using scanning electron microscopy. These microincrements are similar to those deposited daily in the otoliths of fishes from temperate and tropical waters. Microincrements were easily enumerated and fish length was related to increment number by a log-arithmic curve. Otolith microstructure analysis appears to provide a technique to determine age and growth rates accurately in these fish. Sr/Ca ratios in otolith aragonite were analyzed along a radius from the outside edge to the core of an otolith section using an electron microprobe. The Sr/Ca ratios varied with a cyclic periodicity apparently related to seasonal water temperature cycles and the number of cycles agreed closely with age estimated from daily microincrement counts. Sr/Ca cycles can potentially be used to determine age, validate growth rates determined by other methods, and establish thermal conditions experienced during the life of a fish. Microstructural and chemical analyses of otoliths demonstrate great potential in helping to answer many questions about the growth processes and ecology of Antarctic fishes.