RECONSTRUCTING MIGRATORY HISTORY OF FISH USING OTOLITH STRONTIUM:CALCIUMS RATIOS BY EPMA:A CASE STUDY

In this study, the migratory histories of four fish species (tapertail anchovy Coilia nasus and C. mystus, hairtail Trichiurus haumela and longsnout catfish Leiocassis longirostris) in the Yangtze River Estuary, China, were investigated using the otolith Sr:Ca ratios and Sr intensity maps by X-ray electron probe microanalyzer (EPMA). Results showed that, in the C. nasus stock, both river origin anadromous individuals and estuarine origin non-anadromous ones occurred in this area. The otolith Sr:Ca ratios along the life history transects showed 3 general categories of migratory history:2.0×10?3 for river residence, (3.5—6.0) ×10-3 for estuarine residence and 6.0×10-3 for sea residence. In the C. mystus stock, the otolith Sr:Ca ratios also indicated two types of migratory histories:estuary origin and residence in the whole life history (4.8×10-3) and shifting periodically between estuarine residence and sea residence (7.8×10-3) after birth in either water. The otolith Sr : Ca ratios of the hairtail consistently maintained at a high level (4.9×10-3) throughout the life history transects, indicating their whole seawater life. Meanwhile, the low Sr levels in the otoliths of the longsnout catfish suggested that the individuals had freshwater residence all their life stages. These findings confirmed that the oto-lith Sr levels of the four fish species followed an order of seawater residence brackish residence freshwater residence. Due to the influences of the varied environmental histories and the physiology of the fish, the inter-or intra-species differences in the otolith Sr level are remarkable, which is helpful for elementally fingerprinting the migratory history and reconstructing the life history of fish.