Q: In this task, you are given a paragraph in Chinese, and your task is to construct a question in Chinese from the given passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique, and (iv) the answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses the same words or phrases given in the passage. 
鳞首方头鲳（学名：），又称鳞首鲳，为辐鳍鱼纲鲈形目鲳亚目圆鲳科的其中一种。本鱼分布于印度西太平洋区，包括南非、莫三比克、肯亚、索马利亚、留尼旺、模里西斯、印度、日本、韩国、台湾、香港、印尼、菲律宾、澳洲等海域。该物种的模式产地在阿拉伯海。表层至水深80公尺。本鱼中等细长且侧扁，背鳍2枚，硬棘部发育完善，腹鳍比较短，起点在胸鳍基底略后，鳞较大，吻部上方亦有鳞，背鳍、臀鳍鳍条均在20枚左右，体淡色到深褐色, 鱼鳍深色；眼蓝色；幼鱼在尾部基底附近有深色条纹。吻钝，前额些微弓形。上颌无法伸出, 眼大, 直径几乎等于吻的长度, 颌齿小,成单一列，体长可达21公分。本鱼属外洋性鱼类，稚鱼时期喜群聚于漂流物之下，或随潮境漂流或栖息于水母触须下，与水母共生。食用鱼，肉嫩，适合煎食或红烧。
A:
鳞首方头鲳体长可达多少公分？