イシナギ科 Polyprionidae
Wreckfishes
23 アルゼンチンオオハタ
Polyprion americanus
(Bloch and Schneider, 1801) Wreckfish, Bass Groper
Specimen
examined: 1 (SNFR 16601; 651 mm SL), 494–615 m depth.
Counts:
D XI, 12; A III, 9; P1 18; P2
I, 5; GR 6 (5 rudiments)+14 (6 rudiments); LLS 80; V 13+14=27. Measurements: head length 37.4% SL;
body depth 33.8% SL; dorsal-fin base length 48.3% SL; anal-fin base length
14.4% SL; pre-dorsal-fin length 37.2% SL; pre-anus length 70.5% SL;
pectoral-fin length 18.9% SL; pelvic-fin length 17.3% SL; caudal-peduncle
length 19.2% SL; caudal-peduncle depth 11.2% SL; eye diameter 18.8% HL; interorbital width 26.2% HL; snout length 28.7% HL;
upper-jaw length 50.2% HL; lower-jaw length 60.8% 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6（うち痕跡的5）+14（うち痕跡的6）；側線鱗数 80；脊椎骨数13+14=27．計測形質：頭長37.4%
SL；体高33.8%
SL；背鰭基底長48.3%
SL；臀鰭基底長14.4%
SL；背鰭前長37.2%
SL；肛門前長70.5%
SL；胸鰭長18.9%
SL；腹鰭長17.3%
SL；尾柄長19.2%
SL；尾柄高11.2%
SL；眼径18.8%
HL；両眼間隔26.2%
HL；吻長28.7%
HL；上顎長50.2%
HL；下顎長60.8%
HL．
特 徴 体は卵形でやや側扁し，尾柄部は短くて高い．吻は尖り，吻長は眼径よりも長い．両眼間隔域は平坦で，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．前鰓蓋骨の腹側の後縁は鋸歯状．背鰭始部は胸鰭および腹鰭の基部とほぼ同じ垂直線上にある．胸鰭と腹鰭はともに短い．背鰭，腹鰭，および臀鰭の棘条は短くて硬い．肛門は背鰭第1軟条の直下付近に位置する．尾鰭の後縁はやや丸い．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．頭部と体および各鰭はほぼ一様に茶褐色．
分 布 大西洋，地中海，南インド洋，南太平洋西部（Wakefield
et al., 2013）．
備 考 本種は，同属のニュージーランドオオハタP. oxygeneios
(Schneider and Forster, 1801)によく似るが，本種は体高がより高く体長の約30–35%であること（後者は約25–30%），および尾鰭の後縁がやや丸いこと（ほぼ垂直）によって識別できる．本種は全長2
mに達し，水産かつ遊漁の対象魚種である．稚魚は体と頭部に多数の褐色斑をもち，全長約50
cmで表層から底生生活に移る．Ball
et al. (2000) はアルゼンチンオオハタのブラジル産と南太平洋産（オーストラリア，ニュージーランド）のサンプル間で顕著な遺伝的差異を報告している．
（岡本）
Description Body
oval, moderately compressed. Caudal peduncle short and high. Snout protruding,
its length longer than eye diameter. Interorbital
space flat, a bony ridge (supraoccipital crest) on
midline of occipital region. Mouth large, lower jaw projecting 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 serrated. Dorsal-fin origin
located just above bases of pectoral and pelvic fins. Pectoral and pelvic fins
short. Dorsal-, pelvic-, and anal-fin spines short and strong. Anus located
below first soft ray of dorsal fin. Caudal-fin
margin slightly round. Scales small, ctenoid, not
deciduous, covering whole body and head except for lips. Head, body and all
fins uniformly dark brown.
Distribution Atlantic
including
Remarks This
species is similar to P. oxygeneios (Schneider and Forster, 1801), but can be
distinguished by having a deeper body (body depth ca. 30–35% SL vs. ca. 25–30%
SL in P. oxygeneios)
and a slightly rounded caudal fin (vs. truncate). Polyprion americanus reaches two m in total
length, and is a commercially and recreationally targeted species. Juveniles
possess numerous dark blotches on the body and head. When they reach ca. 50 cm
in total length, individuals descend from the pelagic to the demersal zone. Ball et
al. (2000) reported significant genetic differences between specimens of
this species from