Use of the illicium for age determination and verification of yellow goosefish Lophius litulon off Aomori Prefecture, northern Japan

Abstract

Yellow goosefish Lophius litulon is an economically valuable fish species around Japan. The aim of the present study was to evaluate a suitable technique for age determination of yellow goosefish using the illicium. Specimens of yellow goosefish were collected by commercial boats and research vessels from the Sea of Japan, Tsugaru Strait and the Pacific Ocean off Aomori Prefecture from November 2013 to March 2016 using bottom gill, set and trawl nets. Each specimen was measured and sexed, and the illicium and 8th vertebra were removed in the laboratory. The epidermis of each illicium was removed after boiling, and the illicia were dried, whereas each of the 8th vertebra was boiled and sectioned. We found that the best ageing method was a count of opaque zones in the illicia. This was facilitated using the cross-sectioned illicia that had been etched with 1 mol/L HCl for 30 s, stained with methylene blue for 4 h and viewed under transmitted and incident light. Opaque zones form twice per year (mainly during June and November-December) in the illicia. Age determination using opaque zones in the illicia was more accurate than that using opaque zones in the vertebral centra. Because the illicia of yellow goosefish are easy to collect and manipulate for age determination and the growth rate estimated using the illicia and tagging experiments is similar, this method of age determination may be useful for these fish in this region.