山川氏棘花鱸 Plectranthias yamakawai Yoshino, 1972

這裡是另一種棘花鱸的介紹，山川氏棘花鱸 Plectranthias yamakawai Yoshino, 1972，它是台灣海域中裡有分佈，但非常少見的物種。山川氏棘花鱸是在之前文章裡提到的棘花鱸屬裡最大型的物種之一，標準體長可達20cm。前陣子在市場看到一條非常巨型的山川氏棘花鱸，果斷買下來當博物館的標本，買回來後把標準體長量一下(只是用福馬林泡過幾天，只當參考)，那時候這隻個體的標準體長竟然有21.8cm，果然一山還有一山高。

(English description at bottom)

山川氏棘花鱸 Plectranthias yamakawai 是在很早期就被發現且命名的棘花鱸物種。本種在1972由日本學者吉野哲男 Tetsuo Yoshino 發表，但它更早由山川氏及蒲原氏發現並記錄在奄美大島的魚類記錄中 (Kamohara & Yamakawa, 1968)，但並未以新種來發表。在差不多的時間(1967-1970年)，吉野氏在沖繩島的採集了若干尾棘花鱸，當中包括一些黃吻棘花鱸 P. kamii (P. kamii 那時候還沒被描述，所以只是鑑定為 P. anthioides)，同時還有4尾這種(還未發表的)山川氏棘花鱸。之後，加上了1969年由山川氏提供的兩尾在奄美大島採集的樣本，吉野氏在檢視過這些6個標本後判斷了它一個新種，並以山川氏之名命名。

山川氏棘花鱸在大型棘花鱸裡是比較特別的一員，我指大型的都是指可輕易大於15cm，如 P. kamii、P. taylori、P. jothyi (資料很少，最大記錄是15.8cm SL)，以及本種。除了山川氏棘花鱸，上述這些物種的背鰭第三硬棘明顯最長，而山川氏棘花鱸則是背鰭第四硬棘最長。背鰭第三、第四還是第五硬棘最長在棘花鱸裡是一個很穩定的特徵，是重要的鑑別及分類特徵。在大型的大型棘花鱸裡，背鰭第四硬棘最長的物種只有 P. yamakawai。

除了背鰭，體色也是很好的鑑定依據，山川氏棘花鱸之鑑定依據為以下幾點：

1. 體色橘色-橘紅色，各魚鰭(胸鰭除外)以及吻部為黃色；頭部、軀體、背鰭及尾鰭有多顆褐色-黑色點；背鰭第8‒10硬棘的位置、在側線的下方有一顆紅色的大圓斑；側線下方多條黃色斜帶(小個體較明顯)；腹部白色。
2. 尾鰭形狀略為內凹，尾鰭上下葉末端的鰭條稍為延長。腹鰭短，不及肛門位置。
3. 下頜、上頜骨不被鱗；側線上鱗列數5；側線鱗數量為31‒33；頰部斜向鱗列6‒7列；背前鱗只延伸至眼間隔(Interorbital space)之中間。
4. 背鰭 X, 16‒18 (17較多)，第4硬棘最長；胸鰭軟條數 13，最上方鰭條不分叉；臀鰭 III, 7。
5. 前鰓蓋骨下緣有兩根向前棘(Antrorse spine)，上緣鋸齒狀 (26‒31小鋸齒)。

註：非以正式的鑑定格式描述，我把簡單易看的放到前面。

Yoshino (1972) 的發表文獻中，正模標本的繪圖

山川氏棘花鱸在台灣非常少見，雖然在北部、南部及澎湖海域皆有紀錄，但只是偶爾由遊釣船、深水一支釣及底延繩釣上幾隻，而且在魚市場的能見度遠比黃吻及沈氏棘花鱸低許多。本種的分佈主要在台灣及琉球群島，以沖繩島為模式產地，除此它還有在美屬薩摩亞 (American Samoa)被記錄過。本種如的棲息環境與其他大型的棘花鱸差不多，棲息在水深 200‒340米之深水岩礁區域；本種其他生態不清楚，為肉食性魚類，筆者在圖1個體的胃含物裡找到小螃蟹的碎片。

資料整理：
拉丁學名：Plectranthias yamakawai Yoshino, 1972
中文名稱：山川氏棘花鱸、山川棘花鮨
中文俗名：花鱸
日文名稱：アマミハナダイ
最大長度：20.0cm SL
地理分佈：西太平洋海域，台灣、日本琉球群島、美屬薩摩亞 (American Samoa)
模式產地：日本，沖繩島 (Okinawa Island, Japan)


English description:

Plectranthias yamakawai was described by Tetsuo Yoshino in 1972, based on 4 Okinawa specimens collected by himself and 2 specimens from the provided by Yamakawa. Before description, the yamakawa’s perchlet had already recorded in “Additional records of marine fishes from Amami” by T. Kamohara and T. Yamakawa in 1968. However, it was identified as “P. anthioides” that time (which equals to P. kamii) but not recognised as a new species. After Yoshino had examined the specimens, he determined this perchlet as a new species and described it subsequently.

The diagnosis of Plectranthias yamakawai as follows:

1. Two antrorse spines on the ventral margin of the preopercle. Upper margin serrated with ca. 26‒31 serrates.
2. Dorsal-fin elements X, 16‒17(commonly 17), fourth spine longest; pectoral-fin rays 13, uppermost one unbranched; anal-fin elements III, 7.
3. Chin, mandibular, maxilla not scaled.
4. Pored lateral line scales 31‒33; oblique rows of chin scales 6‒7; predorsal scales extended to the middle of the interorbital space.
5. Caudal fin lunated. uppermost and lowermost rays” filamentary; pelvic fin short not reached to anal fin when appressed.
6. Body color reddish yellow, all fins yellow except pectoral fin; head, body, base of dorsal and caudal fin spotted; a large red oval spot below the 8th to 10th D-fin spine.

Plectranthias yamakawai is one of the largest Plectranthias species, its length can exceeds 20cm (in SL) in large adults. The specimen obtained by myself (fig. 1) was measured to be 21.8cm SL (just after few days fixing in formalin). P. yamakawai can be easily distinguished from other large congeners by 1) Fourth dorsal-fin spine longest and 2) Coloration (see the above description). This species should be a typical carnivore, which is believed to prey on small fishes and crustaceans. I have examined the stomach content the specimen (fig. 1), there are pieces of small crab inside.

Plectranthias yamakawai only occurs in the western Pacific region, previously known only from Taiwan and the Ryukyu Islands. It has also been recorded in American Samoa, according to a specimen of Randall. In Taiwan, the yamakawa’s perchlet is known from the northern, southwest and southern part, but it's relatively rare compare to other Plectranthias in Taiwan. It appears as a rare bycatch of deepwater fisheries, caught at depth below 200m.

參考資料：

Yoshino, T. (1972) Plectranthias yamakawai, a New Anthiine Fish from Ryukyu Islands, with a Revision of the Genus Plectranthias. Japanese Journal of Ichthyology, 19 (2), 49‒56.

Randall, J.E. (1980). Revision of the fish genus Plectranthias (Serranidae: Anthiinae) with description of 13 new species. Micronesica, 16, 101‒187.