雄鱼的生殖器是细长条，凹进去。雌鱼为圆形，凸出来。各位可以看看。
在龙鱼之巅有鱼友帖子摘引国外文献在鱼尾鳍有凸起，并不好辨认。我觉得有难度。

这是20cm的时候

还有关于阿根廷和巴西河虎之争，什么大颚小脂鲤，弗朗西斯克。我只能说纯属英文文字咬文嚼字扣出来乱凑的。
国外从来没有哪一篇文献指出巴西河虎叫弗朗西斯克，阿根廷河虎叫大颚小脂鲤。纯属胡说八道。
但黄金河虎确实分为两个产地，巴西产黄金河虎出自圣弗朗西斯科河，市面的黄金河虎主要是此品种；阿根廷产黄金河虎产自巴拉那河及其支流乌拉圭河。
至于外观，两种河虎都可以很黄，也可以很大。我们纪录片经常看到的是巴西河虎，头是斜直的，不那么圆（跟网上一篇盛传的区分贴正好相反），阿根廷出产的河虎头更饱满，弧度更圆润，特别在嘴部。
在阿根廷，黄金河虎由于人为原因数量已经大为稀少，所以已经限制出口了。

所以基本上，市面上不太可能买到所谓阿根廷河虎，所以要注意避免上当受骗。毕竟一批鱼里面，也有头大，头圆的鱼。
河虎算是非常好养的鱼，养定以后不怎么挑食。饲料，虾，鱼都吃。但是刚买的幼鱼有一些会导致开口困难的问题，让人怀疑河虎是否不挑食。
这是建议用活的食蚊鱼或者小草金开食，激活它的捕食欲望。未来可以喂虾，鱼，饲料混合。
我家鱼不吃死鱼肉，只吃饲料，死虾和一切活食。河虎尽量避免混养，即便要混养也要混同体型的底栖鱼，比如恐龙鱼、大型鲶鱼。不过由于鲶鱼生长迅速，要注意鲶鱼长大吞食河虎，有成吉思汗鲨吞掉河虎悲剧发生。
我家河虎咬死过同体型巴西亚，黄金眼镜蛇雷龙和黑魔鲸。如今已经是绝对缸霸，只有两条40的恐龙陪它。
喂食上，尽量不要喂太饱，避免食欲下降情况。如果喂太饱特别是活食，会出现拒食一段时间情况，大约一周多。这是正常，请勿瞎折腾，停食就好了。

我一般一天一条喂一条活泥鳅，它这个体型一口就可以把泥鳅要成两截了，所以不担心伤害肠道情况发生。
喂龟的时候它还会抢食龟粮。
今年我也会进行野化测试，都在野生鱼塘看发色状态。

已收藏

Salminus brasiliensis (dorado, golden dorado, river tiger or jaw characin) is a large, predatory characiform freshwater fish found in central and east-central South America.[1]
Other South American river basins hold relatives of this species: S. franciscanus in the São Francisco Basin, S. hilarii in the upper Paraná, Amazon and Orinoco basins, and S. affinis in the Santiago and Magdalena basins in Ecuador and Colombia.[9]
^ a b c Froese, Rainer and Pauly, Daniel, eds. (2017). "Salminus brasiliensis" in FishBase. February 2017 version.
^ Froese, Rainer, and Daniel Pauly, eds. (2017). Species of Salminus in FishBase. February 2017 version.

这是弗朗西斯科的资料
This species is distinguished from all its congeners, except S. brasiliensis, by the following characters: presence of a second dentary tooth in the outer tooth series that is considerably larger than the remaining teeth (vs. second dentary teeth only slightly larger than remaining teeth in S. affinis and S. hilarii); it differs from S. affinis by the absence of the dark post-orbital stripe (vs. present); differs from S. brasiliensis in having 68-82 (modally 77) lateral line scales (vs. 79-102, modally 96), 11-14 (modally 12) horizontal scales between dorsal-fin origin and lateral line (vs. 14-18, modally 16), and 6-8(modally 6) horizontal scales between lateral line and pelvic-fin insertion (vs. 6-9, modally 8). In spite of the great overlap, compared to the sympatric S. hilarii, this species has generally more scales on the lateral line (vs. 54-72, modally 65-66), horizontal between dorsal-fin origin and lateral line (vs. 9-12, modally 10), and horizontal between lateral line and pelvic-fin insertion (vs. 4-7, modally 5); it also differs by having a golden coloration mainly over the facial bones and pectoral girdle (vs. facial bones and pectoral girdle silvery) (Ref. 75797).
Biology Glossary (e.g. epibenthic)
There is little published information about the general biology and ecology of this species when compared to its much better known S. brasiliensis, even though this species has been recognized as distinct (even if under misapplied names) since late 19th century. Under the name S. brasiliensis, it has been reported to reach one meter in total length and weigh up to 30 kg, consequently, one of the largest known Characiformes; piscivorous; undertakes reproductive migrations during the rainy season; juveniles (< 600 g) were collected in marginal lagoons of the rio São Francisco, an indication that these are recruiting habitats for the species; one of the main targets of the commercial and amateur fisheries in the middle rio São Francisco basin

这是国外权威网上贴的弗朗西斯科照片

我不太愿意掀起老话题引起争论，大家可以对比文字和图片看一下，主要区分在侧线上。
其实在垂钓者眼里两种鱼都一个玩意儿，根本没分。黄金河虎最著名的还是作为垂钓品种。

数数两者尾部侧线数量

就好比草龟里面有些龟头异常大叫大头草。同一种河虎不同生活环境，有的头更大，有的更黄。各位不要被人骗了

群主啊 说下V 详聊 或者加河虎群啥的

这还是去年的照片，今年十几厘米泥鳅一口就是两段。不知道干死我多少鱼，不过对底栖鱼特别友好。