Why does the Torah discuss the fish in between the animals and the birds
Oznayim la'Torah, Because, like the animals, they are permitted with two Simanim ? fins and scales, as opposed to birds, which have four. 1
Midrash Lekach-Tov: The Torah discusses the fish before the birds because in Bereishis, 11:20 that is the order in which they were created
Seeing as the Torah adds "ba'Yamim u'va'Nechalim", why does the Torah mention "ba'Mayim"?
Why does the Torah not specify the names of the fish?
Ba'al ha'Turim ha'Shalem: Because they are invisible to the human eye. 1
Moshav Zekenim (on Pasuk 10): We can say that they do not have names because Adam gave names only to the Behemos, Chayos and birds. 2
Because there are seven hundred 3 Tamei species of fish (Chulin 63b) 4 , and the Torah did not want to list all of them.
Peirush ha'Tur ha'Aruch (which was primarily a Peirush on the Ramban; printers picked out his own Chidushim, and published it as [the standard] Peirush ha'Tur) does not mention this. Also Tinshames (a mole, which burrows underground), Peres and Ozniyah (which are not frequent in settled areas) are not normally seen, and the Torah named them! Perhaps since the Torah named the other Sheratzim and birds, it named also what is not normally seen. (PF)
But not to fish ? presumably because they are invisible to the human eye.
Surely there are more Tahor species, for everything on land has a counterpart at sea, except for a weasel (Chulin 127a)! (PF)
Tosfos (in Chulin, 66b DH 'Kol') - Perhaps it is a tradition from Adam, as the Torah writes in Bereishis, 2:19, "Kol Asher Yikra lo ha'Adam" - including fish. Alternatively, it is a Halachah le'Moshe mi'Sinai.
What is the word "ve'Chol Asher Ein Lo ... " coming to include?
Sifra: It includes species of fish that have bones but do not multiply or that multiply but do hot have bones. 1 in the prohibition.
Both of which cannot possess fins and scales anyway. See Torah Temimahl note 37.
What is the definition of "Kaskeses"?
Rashi, Ramban (citing Chulin, 59a), Targum Onkelos and Targum Yonasan: They are scales 1 (that are fixed to the body ? Rashi). 2
Like those in a suit of armor mentioned in Shmuel 1, 8:5 (Rashi and Ramban).
Anything that is completely attached to the body like the skin does not fall under the heading of "Kaskeses", and what Chazal mean here is that they are static and do not move around like the fins do - but they can be scraped off with a knife (See Ramban).
Why does the Torah write "S'napir ve'Kaskeses" (in the singular)?
Sifra: To teach us that even a fish that has one fin and one scale is KAsher. 1
See Torah Temimah, note 33.
Seeing as all fish that have scales have fins, why does the Torah mentions fins?
Chulin, 66b: 'Lehagdil Torah u'Leha'adirah' ? 'To aggrandize Torah and to glorify it'. 1
See Torah Temimah, note 32.
Why does the Torah insert the (otherwise superfluous) words "Osam Tocheilu"?
What is special about fins and scales?
Moshav Zekenim: The Livyasan has them. 1
Ramban, Moshav Zekenim, Shlah ha'Kadosh (17, and Hagahah): They dwell towards the top of the water and nurture from the air, which makes the body healthy. Fish without fins and scales dwell in stagnant, rotting places. Shlah - also, fins and scales are like a shield, because the fish that possess them are pursued, and not pursuers.
Moshav Zekenim: It is called 'Livyasan' - because the letters spell 'Levai Ten' (give to the nation that accompanies Hashem), and 'Lo Yiten' - everyone in Yisrael will come and say 'give to me.' Levai Ten - everyone who clings to Torah, which was given after fifty days, to him I will give Livyasan. (I do not know how these words hint to fifty - PF.)