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

青森県周辺海域におけるキアンコウの背鰭第一棘による年齢査定法を検証した。背鰭第一棘の付け根付近の横断面をエッチング処理した後，メチレンブルーで染色し，実体顕微鏡下で落射光と透過光の両者による比較観察した結果，不透明帯数の読み取り精度が向上した。同横断面には，1年に2本の不透明帯（主に6月と11–12月）が形成されていた。背鰭第一棘による年齢査定は脊椎骨によるものよりも読み取り誤差が小さく，標識放流魚の成長追跡結果と類似したことから，優れた年齢査定法と判定した。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

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

青森県周辺海域におけるキアンコウの背鰭第一棘による年齢査定法を検証した。背鰭第一棘の付け根付近の横断面をエッチング処理した後，メチレンブルーで染色し，実体顕微鏡下で落射光と透過光の両者による比較観察した結果，不透明帯数の読み取り精度が向上した。同横断面には，1年に2本の不透明帯（主に6月と11–12月）が形成されていた。背鰭第一棘による年齢査定は脊椎骨によるものよりも読み取り誤差が小さく，標識放流魚の成長追跡結果と類似したことから，優れた年齢査定法と判定した。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