(ט) אֶת־זֶה֙ תֹּֽאכְל֔וּ מִכֹּ֖ל אֲשֶׁ֣ר בַּמָּ֑יִם כֹּ֧ל אֲשֶׁר־ל֛וֹ סְנַפִּ֥יר וְקַשְׂקֶ֖שֶׂת תֹּאכֵֽלוּ׃ (י) וְכֹ֨ל אֲשֶׁ֧ר אֵֽין־ל֛וֹ סְנַפִּ֥יר וְקַשְׂקֶ֖שֶׂת לֹ֣א תֹאכֵ֑לוּ טָמֵ֥א ה֖וּא לָכֶֽם׃ {ס}
(9) These you may eat of all that live in water: you may eat anything that has fins and scales. (10) But you may not eat anything that has no fins and scales: it is impure for you.
מתני׳ כל שיש לו קשקשת יש לו סנפיר ויש שיש לו סנפיר ואין לו קשקשת כל שיש לו קרנים יש לו טלפים ויש שיש לו טלפים ואין לו קרנים
MISHNA: It is written: “Whatever has fins and scales in the waters, in the seas, and in the rivers, you may eat them” (Leviticus 11:9). There is a principle with regard to the signs indicating that fish are kosher: Any fish that has scales has fins; and there are fish that have fins but do not have scales. Similarly, with regard to kosher animals it is written: “Whatever parts the hoof, and is wholly cloven-footed, and chews the cud, among the beasts, that you may eat” (Leviticus 11:3). Any animal that has horns has hooves; and there are animals that have hooves but do not have horns.
ולכתוב רחמנא קשקשת ולא בעי סנפיר א"ר אבהו וכן תנא דבי רבי ישמעאל (ישעיהו מב, כא) יגדיל תורה ויאדיר
The Gemara asks: But if there is proof that kaskeset means scales, the question returns: Let the Merciful One write only “scales” and then there would be no need to write “fins.” Rabbi Abbahu says, and likewise a Sage of the school of Rabbi Yishmael taught, that this is in accordance with the verse: “The Lord was pleased, for His righteousness’ sake, to make Torah great and glorious” (Isaiah 42:21).In this context, this means that it is fitting for the Torah to state all the characteristics of a kosher animal rather than merely state that which is absolutely necessary.