イシナギ科　Polyprionidae

イシナギ科　Polyprionidae Wreckfishes

SNFR 17884, 722 mm SL.

24 ニュージーランドオオハタ

Polyprion oxygeneios (Schneider and Forster, 1801) Hapuku, Hapuka, Groper

Specimen examined: 1 (SNFR 17884; 722 mm SL), 358–388 m depth.

Counts: D XI, 12; A III, 9; P₁ 18; P₂ I, 5; GR 7 (6 rudiments)+12 (4 rudiments); LLS 90; V 13+14=27. Measurements: head length 36.6% SL; body depth 27.4% SL; dorsal-fin base length 47.5% SL; anal-fin base length 12.6% SL; predorsal length 37.1% SL; pre-anus length 69.5% SL; pectoral-fin length 15.5% SL; pelvic-fin length 15.9% SL; caudal-peduncle length 18.4% SL; caudal-peduncle depth 9.1% SL; eye diameter 13.3% HL; interorbital width 26.1% HL; snout length 34.0% HL; upper-jaw length 45.5% HL; lower-jaw length 63.7% HL.

計数形質：背鰭11棘，12軟条；臀鰭3棘，9軟条；胸鰭18軟条；腹鰭1棘，5軟条；鰓耙数7（うち痕跡的6）+ 12（うち痕跡的4）；側線鱗数 90；脊椎骨数13+14=27．計測形質：頭長36.6% SL；体高27.4% SL；背鰭基底長47.5% SL；臀鰭基底長12.6% SL；背鰭前長37.1% SL；肛門前長69.5% SL；胸鰭長15.5% SL；腹鰭長15.9% SL；尾柄長18.4% SL；尾柄高9.1% SL；眼径13.3% HL；両眼間隔26.1% HL；吻長34.0% HL；上顎長45.5% HL；下顎長63.7% HL．

特　徴　体は長卵形で側扁し，尾柄部は短くてやや高い．吻は尖り，吻長は両眼間隔よりも長い．眼は小さく，両眼間隔域は平坦．後頭部の背中線上には骨質隆起がある（上後頭骨突起）．口は大きく，下顎は上顎よりも著しく突出する．両顎，鋤骨，口蓋骨，および舌上には絨毛状歯帯がある．主鰓蓋骨棘は強く，骨質隆起を形成する．前鰓蓋骨の後縁は弱い鋸歯状となる．背鰭始部は胸鰭基部とほぼ同じ垂直線上にある．腹鰭基部は胸鰭基部のわずかに後方に位置し，腹鰭長は胸鰭長とほぼ同じ．背鰭，腹鰭，および臀鰭の棘条は短くて硬い．肛門は背鰭第3軟条の直下付近に位置する．尾鰭の後縁は垂直もしくはわずかに湾入する．鱗は小型の櫛鱗で，剥がれにくく，体全体と口唇を除いた頭部を被う．頭部，体側の背部およびすべての鰭が茶褐色で，体側の腹部は淡褐色（固定後）．

分　布　南太平洋西部（オーストラリア沖，ニュージーランド沖），チリ沖，南大西洋中央部（トリスタンダクーニャ諸島），南大西洋西部（ブラジル沖），インド洋南西部（Barreiros et al., 2004；本研究）．

備　考　本種は，同属のアルゼンチンオオハタP. americanus (Bloch and Schneider, 1801)によく似るが，本種は体高が低く体長の約25–30%であること（後者は約30–35%），および尾鰭の後縁がほぼ垂直かわずかに湾入すること（円い）によって識別できる．さらに生鮮時において，本種の体色は青みがかった灰色である（アルゼンチンオオハタは茶色がかった灰色）．本種は全長1.5 mに達し，水産かつ遊漁の対象魚種である．ニュージーランドオオハタとアルゼンチンオオハタの稚魚はともに表層で漂流物に付随していているところを発見されている（Barreiros et al., 2004）．

（岡本）

Description Body long, narrowly oval, compressed, caudal peduncle short and moderately deep. Snout protruded, its length longer than interorbital width. Eye small, interorbital space flat. A bony ridge (supraoccipital crest) on midline of occipital region. Mouth large, lower jaw projecting significantly beyond upper jaw. Villiform tooth bands present on both jaws, vomer, palatine, and tongue. An opercular spine pungent, forming a median ridge. Posteroventral margin of preopercle weakly serrated. Dorsal-fin origin located just above pectoral-fin base. Pelvic-fin base slightly posterior to pectoral-fin base, pelvic-fin length subequal to pectoral-fin length. Dorsal-, pelvic-, and anal-fin spines short and robust. Anus located below third soft ray of dorsal fin. Caudal fin truncate or slightly concave. Scales small ctenoid, not deciduous, covering whole body and head except for lips. Head, dorsolateral body, and all fins dark brown, and ventrolateral body light brown (in preservative).

Distribution Western South Pacific (off Australia and New Zealand), off Chile, central South Atlantic (Tristan da Cunha Group), western South Atlantic (off Brazil), western South Indian Ocean (Barreiros et al., 2004; present study).

Remarks This species is similar to P. americanus (Bloch and Schneider, 1801), but can be distinguished by having a shallower body (body depth ca. 25–30% SL vs. ca. 30–35% SL in P. americanus) and a truncate or slightly concave caudal fin (vs. rounded). In addition, P. oxygeneios in fresh condition is bluish grey laterally (vs. brownish grey in P. americanus). Polyprion oxygeneios reaches 1.5 m in total length, and is a commercially and recreationally targeted species. Juveniles of P. americanus and P. oxygeneios are found at the surface associated with drifting material (Barreiros et al., 2004).

(M. Okamoto)