Validation of daily increments in the otolith microstructure of sailfin sandfish, Arctoscopus japonicus, larvae in Erimo [Japan], the Pacific coast of Hokkaido
2009
Yoshimura, K., Hokkaido. Mariculture Fisheries Experiment Station, Muroran (Japan) | Tsutsui, D. | Maeda, K. | Sannohe, M. | Haga, K.
The otolith microstructure of larval sailfin sandfish, Arctoscopus japonicus, was studied at Erimo, on the Pacific coast of Hokkaido. Compared to the populations in the Sea of Japan, this local population experiences noticiably colder water temperature during eggs and larval stage by the influence of the Oyashio current. We attempted to find an appropriate ageing technique for this population using artificially fertilized eggs in December 2004. We reared larvae from March to May 2005, aged 0 to 60 days and examined at 10-day intervals. The lapilli provided apparently lower incremental counts to age under optical microscopy (mean+-SD: -21.1+-4.5), in spite of a previous study had recommended as precisely representing daily increments. We hypothesize that the relatively smaller size of lapilli to the body and very cold rearing water temperature resulted in narrower increments. In addition, there were many invisible increments around the hatch check, resulting in considerable counting error. In the sagittae, regular concentric rings were found and increment counts were closely correlated with age (-2.8+-1.9). Again, some increments around the hatch check were difficult to resolve, but the estimated increment deposition rate between 30-60 days was one per day. The sagittae of larger juveniles (N=5: 30.5-35.7mm in TL) exhibited some accessory layers around the edge. However, these increments had regular deposition and it was possible to track growth. We conclude that in this population, the analyses of daily increments should be performed with sagittae, not lapilli.
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